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![Daniel Axtens](/assets/img/avatar_default.png)
The memcmp KASAN self-test fails on a kernel with both KASAN and FORTIFY_SOURCE. When FORTIFY_SOURCE is on, a number of functions are replaced with fortified versions, which attempt to check the sizes of the operands. However, these functions often directly invoke __builtin_foo() once they have performed the fortify check. Using __builtins may bypass KASAN checks if the compiler decides to inline it's own implementation as sequence of instructions, rather than emit a function call that goes out to a KASAN-instrumented implementation. Why is only memcmp affected? ============================ Of the string and string-like functions that kasan_test tests, only memcmp is replaced by an inline sequence of instructions in my testing on x86 with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2). I believe this is due to compiler heuristics. For example, if I annotate kmalloc calls with the alloc_size annotation (and disable some fortify compile-time checking!), the compiler will replace every memset except the one in kmalloc_uaf_memset with inline instructions. (I have some WIP patches to add this annotation.) Does this affect other functions in string.h? ============================================= Yes. Anything that uses __builtin_* rather than __real_* could be affected. This looks like: - strncpy - strcat - strlen - strlcpy maybe, under some circumstances? - strncat under some circumstances - memset - memcpy - memmove - memcmp (as noted) - memchr - strcpy Whether a function call is emitted always depends on the compiler. Most bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows that this is not always the case. Isn't FORTIFY_SOURCE disabled with KASAN? ========================================- The string headers on all arches supporting KASAN disable fortify with kasan, but only when address sanitisation is _also_ disabled. For example from x86: #if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__) /* * For files that are not instrumented (e.g. mm/slub.c) we * should use not instrumented version of mem* functions. */ #define memcpy(dst, src, len) __memcpy(dst, src, len) #define memmove(dst, src, len) __memmove(dst, src, len) #define memset(s, c, n) __memset(s, c, n) #ifndef __NO_FORTIFY #define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */ #endif #endif This comes from commit6974f0c455
("include/linux/string.h: add the option of fortified string.h functions"), and doesn't work when KASAN is enabled and the file is supposed to be sanitised - as with test_kasan.c I'm pretty sure this is not wrong, but not as expansive it should be: * we shouldn't use __builtin_memcpy etc in files where we don't have instrumentation - it could devolve into a function call to memcpy, which will be instrumented. Rather, we should use __memcpy which by convention is not instrumented. * we also shouldn't be using __builtin_memcpy when we have a KASAN instrumented file, because it could be replaced with inline asm that will not be instrumented. What is correct behaviour? ========================== Firstly, there is some overlap between fortification and KASAN: both provide some level of _runtime_ checking. Only fortify provides compile-time checking. KASAN and fortify can pick up different things at runtime: - Some fortify functions, notably the string functions, could easily be modified to consider sub-object sizes (e.g. members within a struct), and I have some WIP patches to do this. KASAN cannot detect these because it cannot insert poision between members of a struct. - KASAN can detect many over-reads/over-writes when the sizes of both operands are unknown, which fortify cannot. So there are a couple of options: 1) Flip the test: disable fortify in santised files and enable it in unsanitised files. This at least stops us missing KASAN checking, but we lose the fortify checking. 2) Make the fortify code always call out to real versions. Do this only for KASAN, for fear of losing the inlining opportunities we get from __builtin_*. (We can't use kasan_check_{read,write}: because the fortify functions are _extern inline_, you can't include _static_ inline functions without a compiler warning. kasan_check_{read,write} are static inline so we can't use them even when they would otherwise be suitable.) Take approach 2 and call out to real versions when KASAN is enabled. Use __underlying_foo to distinguish from __real_foo: __real_foo always refers to the kernel's implementation of foo, __underlying_foo could be either the kernel implementation or the __builtin_foo implementation. This is sometimes enough to make the memcmp test succeed with FORTIFY_SOURCE enabled. It is at least enough to get the function call into the module. One more fix is needed to make it reliable: see the next patch. Fixes:6974f0c455
("include/linux/string.h: add the option of fortified string.h functions") Signed-off-by: Daniel Axtens <dja@axtens.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Tested-by: David Gow <davidgow@google.com> Reviewed-by: Dmitry Vyukov <dvyukov@google.com> Cc: Daniel Micay <danielmicay@gmail.com> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Alexander Potapenko <glider@google.com> Link: http://lkml.kernel.org/r/20200423154503.5103-3-dja@axtens.net Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
545 lines
17 KiB
C
545 lines
17 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_STRING_H_
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#define _LINUX_STRING_H_
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#include <linux/compiler.h> /* for inline */
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#include <linux/types.h> /* for size_t */
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#include <linux/stddef.h> /* for NULL */
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#include <stdarg.h>
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#include <uapi/linux/string.h>
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extern char *strndup_user(const char __user *, long);
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extern void *memdup_user(const void __user *, size_t);
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extern void *vmemdup_user(const void __user *, size_t);
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extern void *memdup_user_nul(const void __user *, size_t);
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/*
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* Include machine specific inline routines
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*/
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#include <asm/string.h>
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#ifndef __HAVE_ARCH_STRCPY
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extern char * strcpy(char *,const char *);
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#endif
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#ifndef __HAVE_ARCH_STRNCPY
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extern char * strncpy(char *,const char *, __kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_STRLCPY
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size_t strlcpy(char *, const char *, size_t);
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#endif
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#ifndef __HAVE_ARCH_STRSCPY
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ssize_t strscpy(char *, const char *, size_t);
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#endif
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/* Wraps calls to strscpy()/memset(), no arch specific code required */
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ssize_t strscpy_pad(char *dest, const char *src, size_t count);
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#ifndef __HAVE_ARCH_STRCAT
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extern char * strcat(char *, const char *);
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#endif
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#ifndef __HAVE_ARCH_STRNCAT
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extern char * strncat(char *, const char *, __kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_STRLCAT
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extern size_t strlcat(char *, const char *, __kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_STRCMP
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extern int strcmp(const char *,const char *);
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#endif
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#ifndef __HAVE_ARCH_STRNCMP
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extern int strncmp(const char *,const char *,__kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_STRCASECMP
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extern int strcasecmp(const char *s1, const char *s2);
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#endif
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#ifndef __HAVE_ARCH_STRNCASECMP
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extern int strncasecmp(const char *s1, const char *s2, size_t n);
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#endif
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#ifndef __HAVE_ARCH_STRCHR
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extern char * strchr(const char *,int);
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#endif
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#ifndef __HAVE_ARCH_STRCHRNUL
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extern char * strchrnul(const char *,int);
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#endif
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extern char * strnchrnul(const char *, size_t, int);
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#ifndef __HAVE_ARCH_STRNCHR
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extern char * strnchr(const char *, size_t, int);
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#endif
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#ifndef __HAVE_ARCH_STRRCHR
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extern char * strrchr(const char *,int);
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#endif
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extern char * __must_check skip_spaces(const char *);
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extern char *strim(char *);
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static inline __must_check char *strstrip(char *str)
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{
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return strim(str);
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}
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#ifndef __HAVE_ARCH_STRSTR
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extern char * strstr(const char *, const char *);
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#endif
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#ifndef __HAVE_ARCH_STRNSTR
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extern char * strnstr(const char *, const char *, size_t);
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#endif
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#ifndef __HAVE_ARCH_STRLEN
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extern __kernel_size_t strlen(const char *);
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#endif
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#ifndef __HAVE_ARCH_STRNLEN
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extern __kernel_size_t strnlen(const char *,__kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_STRPBRK
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extern char * strpbrk(const char *,const char *);
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#endif
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#ifndef __HAVE_ARCH_STRSEP
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extern char * strsep(char **,const char *);
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#endif
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#ifndef __HAVE_ARCH_STRSPN
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extern __kernel_size_t strspn(const char *,const char *);
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#endif
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#ifndef __HAVE_ARCH_STRCSPN
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extern __kernel_size_t strcspn(const char *,const char *);
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#endif
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#ifndef __HAVE_ARCH_MEMSET
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extern void * memset(void *,int,__kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_MEMSET16
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extern void *memset16(uint16_t *, uint16_t, __kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_MEMSET32
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extern void *memset32(uint32_t *, uint32_t, __kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_MEMSET64
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extern void *memset64(uint64_t *, uint64_t, __kernel_size_t);
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#endif
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static inline void *memset_l(unsigned long *p, unsigned long v,
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__kernel_size_t n)
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{
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if (BITS_PER_LONG == 32)
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return memset32((uint32_t *)p, v, n);
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else
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return memset64((uint64_t *)p, v, n);
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}
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static inline void *memset_p(void **p, void *v, __kernel_size_t n)
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{
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if (BITS_PER_LONG == 32)
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return memset32((uint32_t *)p, (uintptr_t)v, n);
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else
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return memset64((uint64_t *)p, (uintptr_t)v, n);
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}
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extern void **__memcat_p(void **a, void **b);
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#define memcat_p(a, b) ({ \
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BUILD_BUG_ON_MSG(!__same_type(*(a), *(b)), \
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"type mismatch in memcat_p()"); \
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(typeof(*a) *)__memcat_p((void **)(a), (void **)(b)); \
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})
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#ifndef __HAVE_ARCH_MEMCPY
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extern void * memcpy(void *,const void *,__kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_MEMMOVE
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extern void * memmove(void *,const void *,__kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_MEMSCAN
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extern void * memscan(void *,int,__kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_MEMCMP
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extern int memcmp(const void *,const void *,__kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_BCMP
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extern int bcmp(const void *,const void *,__kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_MEMCHR
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extern void * memchr(const void *,int,__kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_MEMCPY_MCSAFE
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static inline __must_check unsigned long memcpy_mcsafe(void *dst,
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const void *src, size_t cnt)
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{
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memcpy(dst, src, cnt);
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return 0;
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}
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#endif
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#ifndef __HAVE_ARCH_MEMCPY_FLUSHCACHE
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static inline void memcpy_flushcache(void *dst, const void *src, size_t cnt)
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{
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memcpy(dst, src, cnt);
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}
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#endif
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void *memchr_inv(const void *s, int c, size_t n);
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char *strreplace(char *s, char old, char new);
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extern void kfree_const(const void *x);
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extern char *kstrdup(const char *s, gfp_t gfp) __malloc;
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extern const char *kstrdup_const(const char *s, gfp_t gfp);
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extern char *kstrndup(const char *s, size_t len, gfp_t gfp);
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extern void *kmemdup(const void *src, size_t len, gfp_t gfp);
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extern char *kmemdup_nul(const char *s, size_t len, gfp_t gfp);
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extern char **argv_split(gfp_t gfp, const char *str, int *argcp);
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extern void argv_free(char **argv);
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extern bool sysfs_streq(const char *s1, const char *s2);
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extern int kstrtobool(const char *s, bool *res);
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static inline int strtobool(const char *s, bool *res)
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{
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return kstrtobool(s, res);
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}
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int match_string(const char * const *array, size_t n, const char *string);
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int __sysfs_match_string(const char * const *array, size_t n, const char *s);
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/**
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* sysfs_match_string - matches given string in an array
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* @_a: array of strings
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* @_s: string to match with
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*
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* Helper for __sysfs_match_string(). Calculates the size of @a automatically.
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*/
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#define sysfs_match_string(_a, _s) __sysfs_match_string(_a, ARRAY_SIZE(_a), _s)
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#ifdef CONFIG_BINARY_PRINTF
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int vbin_printf(u32 *bin_buf, size_t size, const char *fmt, va_list args);
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int bstr_printf(char *buf, size_t size, const char *fmt, const u32 *bin_buf);
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int bprintf(u32 *bin_buf, size_t size, const char *fmt, ...) __printf(3, 4);
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#endif
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extern ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos,
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const void *from, size_t available);
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int ptr_to_hashval(const void *ptr, unsigned long *hashval_out);
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/**
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* strstarts - does @str start with @prefix?
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* @str: string to examine
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* @prefix: prefix to look for.
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*/
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static inline bool strstarts(const char *str, const char *prefix)
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{
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return strncmp(str, prefix, strlen(prefix)) == 0;
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}
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size_t memweight(const void *ptr, size_t bytes);
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/**
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* memzero_explicit - Fill a region of memory (e.g. sensitive
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* keying data) with 0s.
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* @s: Pointer to the start of the area.
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* @count: The size of the area.
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*
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* Note: usually using memset() is just fine (!), but in cases
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* where clearing out _local_ data at the end of a scope is
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* necessary, memzero_explicit() should be used instead in
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* order to prevent the compiler from optimising away zeroing.
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*
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* memzero_explicit() doesn't need an arch-specific version as
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* it just invokes the one of memset() implicitly.
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*/
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static inline void memzero_explicit(void *s, size_t count)
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{
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memset(s, 0, count);
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barrier_data(s);
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}
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/**
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* kbasename - return the last part of a pathname.
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*
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* @path: path to extract the filename from.
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*/
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static inline const char *kbasename(const char *path)
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{
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const char *tail = strrchr(path, '/');
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return tail ? tail + 1 : path;
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}
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#define __FORTIFY_INLINE extern __always_inline __attribute__((gnu_inline))
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#define __RENAME(x) __asm__(#x)
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void fortify_panic(const char *name) __noreturn __cold;
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void __read_overflow(void) __compiletime_error("detected read beyond size of object passed as 1st parameter");
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void __read_overflow2(void) __compiletime_error("detected read beyond size of object passed as 2nd parameter");
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void __read_overflow3(void) __compiletime_error("detected read beyond size of object passed as 3rd parameter");
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void __write_overflow(void) __compiletime_error("detected write beyond size of object passed as 1st parameter");
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#if !defined(__NO_FORTIFY) && defined(__OPTIMIZE__) && defined(CONFIG_FORTIFY_SOURCE)
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#ifdef CONFIG_KASAN
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extern void *__underlying_memchr(const void *p, int c, __kernel_size_t size) __RENAME(memchr);
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extern int __underlying_memcmp(const void *p, const void *q, __kernel_size_t size) __RENAME(memcmp);
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extern void *__underlying_memcpy(void *p, const void *q, __kernel_size_t size) __RENAME(memcpy);
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extern void *__underlying_memmove(void *p, const void *q, __kernel_size_t size) __RENAME(memmove);
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extern void *__underlying_memset(void *p, int c, __kernel_size_t size) __RENAME(memset);
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extern char *__underlying_strcat(char *p, const char *q) __RENAME(strcat);
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extern char *__underlying_strcpy(char *p, const char *q) __RENAME(strcpy);
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extern __kernel_size_t __underlying_strlen(const char *p) __RENAME(strlen);
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extern char *__underlying_strncat(char *p, const char *q, __kernel_size_t count) __RENAME(strncat);
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extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) __RENAME(strncpy);
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#else
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#define __underlying_memchr __builtin_memchr
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#define __underlying_memcmp __builtin_memcmp
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#define __underlying_memcpy __builtin_memcpy
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#define __underlying_memmove __builtin_memmove
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#define __underlying_memset __builtin_memset
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#define __underlying_strcat __builtin_strcat
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#define __underlying_strcpy __builtin_strcpy
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#define __underlying_strlen __builtin_strlen
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#define __underlying_strncat __builtin_strncat
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#define __underlying_strncpy __builtin_strncpy
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#endif
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__FORTIFY_INLINE char *strncpy(char *p, const char *q, __kernel_size_t size)
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{
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size_t p_size = __builtin_object_size(p, 0);
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if (__builtin_constant_p(size) && p_size < size)
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__write_overflow();
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if (p_size < size)
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fortify_panic(__func__);
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return __underlying_strncpy(p, q, size);
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}
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__FORTIFY_INLINE char *strcat(char *p, const char *q)
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{
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size_t p_size = __builtin_object_size(p, 0);
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if (p_size == (size_t)-1)
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return __underlying_strcat(p, q);
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if (strlcat(p, q, p_size) >= p_size)
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fortify_panic(__func__);
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return p;
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}
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__FORTIFY_INLINE __kernel_size_t strlen(const char *p)
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{
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__kernel_size_t ret;
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size_t p_size = __builtin_object_size(p, 0);
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/* Work around gcc excess stack consumption issue */
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if (p_size == (size_t)-1 ||
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(__builtin_constant_p(p[p_size - 1]) && p[p_size - 1] == '\0'))
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return __underlying_strlen(p);
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ret = strnlen(p, p_size);
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if (p_size <= ret)
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fortify_panic(__func__);
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return ret;
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}
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extern __kernel_size_t __real_strnlen(const char *, __kernel_size_t) __RENAME(strnlen);
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__FORTIFY_INLINE __kernel_size_t strnlen(const char *p, __kernel_size_t maxlen)
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{
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size_t p_size = __builtin_object_size(p, 0);
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__kernel_size_t ret = __real_strnlen(p, maxlen < p_size ? maxlen : p_size);
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if (p_size <= ret && maxlen != ret)
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fortify_panic(__func__);
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return ret;
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}
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/* defined after fortified strlen to reuse it */
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extern size_t __real_strlcpy(char *, const char *, size_t) __RENAME(strlcpy);
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__FORTIFY_INLINE size_t strlcpy(char *p, const char *q, size_t size)
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{
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size_t ret;
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size_t p_size = __builtin_object_size(p, 0);
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size_t q_size = __builtin_object_size(q, 0);
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if (p_size == (size_t)-1 && q_size == (size_t)-1)
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return __real_strlcpy(p, q, size);
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ret = strlen(q);
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if (size) {
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size_t len = (ret >= size) ? size - 1 : ret;
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if (__builtin_constant_p(len) && len >= p_size)
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__write_overflow();
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if (len >= p_size)
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fortify_panic(__func__);
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__underlying_memcpy(p, q, len);
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p[len] = '\0';
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}
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return ret;
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}
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/* defined after fortified strlen and strnlen to reuse them */
|
|
__FORTIFY_INLINE char *strncat(char *p, const char *q, __kernel_size_t count)
|
|
{
|
|
size_t p_len, copy_len;
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
size_t q_size = __builtin_object_size(q, 0);
|
|
if (p_size == (size_t)-1 && q_size == (size_t)-1)
|
|
return __underlying_strncat(p, q, count);
|
|
p_len = strlen(p);
|
|
copy_len = strnlen(q, count);
|
|
if (p_size < p_len + copy_len + 1)
|
|
fortify_panic(__func__);
|
|
__underlying_memcpy(p + p_len, q, copy_len);
|
|
p[p_len + copy_len] = '\0';
|
|
return p;
|
|
}
|
|
|
|
__FORTIFY_INLINE void *memset(void *p, int c, __kernel_size_t size)
|
|
{
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
if (__builtin_constant_p(size) && p_size < size)
|
|
__write_overflow();
|
|
if (p_size < size)
|
|
fortify_panic(__func__);
|
|
return __underlying_memset(p, c, size);
|
|
}
|
|
|
|
__FORTIFY_INLINE void *memcpy(void *p, const void *q, __kernel_size_t size)
|
|
{
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
size_t q_size = __builtin_object_size(q, 0);
|
|
if (__builtin_constant_p(size)) {
|
|
if (p_size < size)
|
|
__write_overflow();
|
|
if (q_size < size)
|
|
__read_overflow2();
|
|
}
|
|
if (p_size < size || q_size < size)
|
|
fortify_panic(__func__);
|
|
return __underlying_memcpy(p, q, size);
|
|
}
|
|
|
|
__FORTIFY_INLINE void *memmove(void *p, const void *q, __kernel_size_t size)
|
|
{
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
size_t q_size = __builtin_object_size(q, 0);
|
|
if (__builtin_constant_p(size)) {
|
|
if (p_size < size)
|
|
__write_overflow();
|
|
if (q_size < size)
|
|
__read_overflow2();
|
|
}
|
|
if (p_size < size || q_size < size)
|
|
fortify_panic(__func__);
|
|
return __underlying_memmove(p, q, size);
|
|
}
|
|
|
|
extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan);
|
|
__FORTIFY_INLINE void *memscan(void *p, int c, __kernel_size_t size)
|
|
{
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
if (__builtin_constant_p(size) && p_size < size)
|
|
__read_overflow();
|
|
if (p_size < size)
|
|
fortify_panic(__func__);
|
|
return __real_memscan(p, c, size);
|
|
}
|
|
|
|
__FORTIFY_INLINE int memcmp(const void *p, const void *q, __kernel_size_t size)
|
|
{
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
size_t q_size = __builtin_object_size(q, 0);
|
|
if (__builtin_constant_p(size)) {
|
|
if (p_size < size)
|
|
__read_overflow();
|
|
if (q_size < size)
|
|
__read_overflow2();
|
|
}
|
|
if (p_size < size || q_size < size)
|
|
fortify_panic(__func__);
|
|
return __underlying_memcmp(p, q, size);
|
|
}
|
|
|
|
__FORTIFY_INLINE void *memchr(const void *p, int c, __kernel_size_t size)
|
|
{
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
if (__builtin_constant_p(size) && p_size < size)
|
|
__read_overflow();
|
|
if (p_size < size)
|
|
fortify_panic(__func__);
|
|
return __underlying_memchr(p, c, size);
|
|
}
|
|
|
|
void *__real_memchr_inv(const void *s, int c, size_t n) __RENAME(memchr_inv);
|
|
__FORTIFY_INLINE void *memchr_inv(const void *p, int c, size_t size)
|
|
{
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
if (__builtin_constant_p(size) && p_size < size)
|
|
__read_overflow();
|
|
if (p_size < size)
|
|
fortify_panic(__func__);
|
|
return __real_memchr_inv(p, c, size);
|
|
}
|
|
|
|
extern void *__real_kmemdup(const void *src, size_t len, gfp_t gfp) __RENAME(kmemdup);
|
|
__FORTIFY_INLINE void *kmemdup(const void *p, size_t size, gfp_t gfp)
|
|
{
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
if (__builtin_constant_p(size) && p_size < size)
|
|
__read_overflow();
|
|
if (p_size < size)
|
|
fortify_panic(__func__);
|
|
return __real_kmemdup(p, size, gfp);
|
|
}
|
|
|
|
/* defined after fortified strlen and memcpy to reuse them */
|
|
__FORTIFY_INLINE char *strcpy(char *p, const char *q)
|
|
{
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
size_t q_size = __builtin_object_size(q, 0);
|
|
if (p_size == (size_t)-1 && q_size == (size_t)-1)
|
|
return __underlying_strcpy(p, q);
|
|
memcpy(p, q, strlen(q) + 1);
|
|
return p;
|
|
}
|
|
|
|
/* Don't use these outside the FORITFY_SOURCE implementation */
|
|
#undef __underlying_memchr
|
|
#undef __underlying_memcmp
|
|
#undef __underlying_memcpy
|
|
#undef __underlying_memmove
|
|
#undef __underlying_memset
|
|
#undef __underlying_strcat
|
|
#undef __underlying_strcpy
|
|
#undef __underlying_strlen
|
|
#undef __underlying_strncat
|
|
#undef __underlying_strncpy
|
|
#endif
|
|
|
|
/**
|
|
* memcpy_and_pad - Copy one buffer to another with padding
|
|
* @dest: Where to copy to
|
|
* @dest_len: The destination buffer size
|
|
* @src: Where to copy from
|
|
* @count: The number of bytes to copy
|
|
* @pad: Character to use for padding if space is left in destination.
|
|
*/
|
|
static inline void memcpy_and_pad(void *dest, size_t dest_len,
|
|
const void *src, size_t count, int pad)
|
|
{
|
|
if (dest_len > count) {
|
|
memcpy(dest, src, count);
|
|
memset(dest + count, pad, dest_len - count);
|
|
} else
|
|
memcpy(dest, src, dest_len);
|
|
}
|
|
|
|
/**
|
|
* str_has_prefix - Test if a string has a given prefix
|
|
* @str: The string to test
|
|
* @prefix: The string to see if @str starts with
|
|
*
|
|
* A common way to test a prefix of a string is to do:
|
|
* strncmp(str, prefix, sizeof(prefix) - 1)
|
|
*
|
|
* But this can lead to bugs due to typos, or if prefix is a pointer
|
|
* and not a constant. Instead use str_has_prefix().
|
|
*
|
|
* Returns:
|
|
* * strlen(@prefix) if @str starts with @prefix
|
|
* * 0 if @str does not start with @prefix
|
|
*/
|
|
static __always_inline size_t str_has_prefix(const char *str, const char *prefix)
|
|
{
|
|
size_t len = strlen(prefix);
|
|
return strncmp(str, prefix, len) == 0 ? len : 0;
|
|
}
|
|
|
|
#endif /* _LINUX_STRING_H_ */
|