string: Allow 2-argument strscpy()

Using sizeof(dst) for the "size" argument in strscpy() is the
overwhelmingly common case. Instead of requiring this everywhere, allow a
2-argument version to be used that will use the sizeof() internally. There
are other functions in the kernel with optional arguments[1], so this
isn't unprecedented, and improves readability. Update and relocate the
kern-doc for strscpy() too, and drop __HAVE_ARCH_STRSCPY as it is unused.

Adjust ARCH=um build to notice the changed export name, as it doesn't
do full header includes for the string helpers.

This could additionally let us save a few hundred lines of code:
 1177 files changed, 2455 insertions(+), 3026 deletions(-)
with a treewide cleanup using Coccinelle:

@needless_arg@
expression DST, SRC;
@@

        strscpy(DST, SRC
-, sizeof(DST)
        )

Link: https://elixir.bootlin.com/linux/v6.7/source/include/linux/pci.h#L1517 [1]
Reviewed-by: Justin Stitt <justinstitt@google.com>
Cc: Andy Shevchenko <andy@kernel.org>
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Kees Cook 2023-09-20 12:38:14 -07:00
parent f478898e0a
commit e6584c3964
4 changed files with 41 additions and 28 deletions

View File

@ -51,7 +51,8 @@ static inline int printk(const char *fmt, ...)
extern int in_aton(char *str); extern int in_aton(char *str);
extern size_t strlcat(char *, const char *, size_t); extern size_t strlcat(char *, const char *, size_t);
extern size_t strscpy(char *, const char *, size_t); extern size_t sized_strscpy(char *, const char *, size_t);
#define strscpy(dst, src, size) sized_strscpy(dst, src, size)
/* Copied from linux/compiler-gcc.h since we can't include it directly */ /* Copied from linux/compiler-gcc.h since we can't include it directly */
#define barrier() __asm__ __volatile__("": : :"memory") #define barrier() __asm__ __volatile__("": : :"memory")

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@ -215,26 +215,8 @@ __kernel_size_t __fortify_strlen(const char * const POS p)
} }
/* Defined after fortified strnlen() to reuse it. */ /* Defined after fortified strnlen() to reuse it. */
extern ssize_t __real_strscpy(char *, const char *, size_t) __RENAME(strscpy); extern ssize_t __real_strscpy(char *, const char *, size_t) __RENAME(sized_strscpy);
/** __FORTIFY_INLINE ssize_t sized_strscpy(char * const POS p, const char * const POS q, size_t size)
* strscpy - Copy a C-string into a sized buffer
*
* @p: Where to copy the string to
* @q: Where to copy the string from
* @size: Size of destination buffer
*
* Copy the source string @q, or as much of it as fits, into the destination
* @p buffer. The behavior is undefined if the string buffers overlap. The
* destination @p buffer is always NUL terminated, unless it's zero-sized.
*
* Preferred to strncpy() since it always returns a valid string, and
* doesn't unnecessarily force the tail of the destination buffer to be
* zero padded. If padding is desired please use strscpy_pad().
*
* Returns the number of characters copied in @p (not including the
* trailing %NUL) or -E2BIG if @size is 0 or the copy of @q was truncated.
*/
__FORTIFY_INLINE ssize_t strscpy(char * const POS p, const char * const POS q, size_t size)
{ {
/* Use string size rather than possible enclosing struct size. */ /* Use string size rather than possible enclosing struct size. */
const size_t p_size = __member_size(p); const size_t p_size = __member_size(p);

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@ -2,6 +2,7 @@
#ifndef _LINUX_STRING_H_ #ifndef _LINUX_STRING_H_
#define _LINUX_STRING_H_ #define _LINUX_STRING_H_
#include <linux/args.h>
#include <linux/array_size.h> #include <linux/array_size.h>
#include <linux/compiler.h> /* for inline */ #include <linux/compiler.h> /* for inline */
#include <linux/types.h> /* for size_t */ #include <linux/types.h> /* for size_t */
@ -66,9 +67,40 @@ extern char * strcpy(char *,const char *);
#ifndef __HAVE_ARCH_STRNCPY #ifndef __HAVE_ARCH_STRNCPY
extern char * strncpy(char *,const char *, __kernel_size_t); extern char * strncpy(char *,const char *, __kernel_size_t);
#endif #endif
#ifndef __HAVE_ARCH_STRSCPY ssize_t sized_strscpy(char *, const char *, size_t);
ssize_t strscpy(char *, const char *, size_t);
#endif /*
* The 2 argument style can only be used when dst is an array with a
* known size.
*/
#define __strscpy0(dst, src, ...) \
sized_strscpy(dst, src, sizeof(dst) + __must_be_array(dst))
#define __strscpy1(dst, src, size) sized_strscpy(dst, src, size)
/**
* strscpy - Copy a C-string into a sized buffer
* @dst: Where to copy the string to
* @src: Where to copy the string from
* @...: Size of destination buffer (optional)
*
* Copy the source string @src, or as much of it as fits, into the
* destination @dst buffer. The behavior is undefined if the string
* buffers overlap. The destination @dst buffer is always NUL terminated,
* unless it's zero-sized.
*
* The size argument @... is only required when @dst is not an array, or
* when the copy needs to be smaller than sizeof(@dst).
*
* Preferred to strncpy() since it always returns a valid string, and
* doesn't unnecessarily force the tail of the destination buffer to be
* zero padded. If padding is desired please use strscpy_pad().
*
* Returns the number of characters copied in @dst (not including the
* trailing %NUL) or -E2BIG if @size is 0 or the copy from @src was
* truncated.
*/
#define strscpy(dst, src, ...) \
CONCATENATE(__strscpy, COUNT_ARGS(__VA_ARGS__))(dst, src, __VA_ARGS__)
/** /**
* strscpy_pad() - Copy a C-string into a sized buffer * strscpy_pad() - Copy a C-string into a sized buffer

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@ -104,8 +104,7 @@ char *strncpy(char *dest, const char *src, size_t count)
EXPORT_SYMBOL(strncpy); EXPORT_SYMBOL(strncpy);
#endif #endif
#ifndef __HAVE_ARCH_STRSCPY ssize_t sized_strscpy(char *dest, const char *src, size_t count)
ssize_t strscpy(char *dest, const char *src, size_t count)
{ {
const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
size_t max = count; size_t max = count;
@ -171,8 +170,7 @@ ssize_t strscpy(char *dest, const char *src, size_t count)
return -E2BIG; return -E2BIG;
} }
EXPORT_SYMBOL(strscpy); EXPORT_SYMBOL(sized_strscpy);
#endif
/** /**
* stpcpy - copy a string from src to dest returning a pointer to the new end * stpcpy - copy a string from src to dest returning a pointer to the new end