From 4ce615e798a752d4431fcc52960478906dec2f0e Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Fri, 7 Apr 2023 12:27:14 -0700 Subject: [PATCH] fortify: Provide KUnit counters for failure testing The standard C string APIs were not designed to have a failure mode; they were expected to always succeed without memory safety issues. Normally, CONFIG_FORTIFY_SOURCE will use fortify_panic() to stop processing, as truncating a read or write may provide an even worse system state. However, this creates a problem for testing under things like KUnit, which needs a way to survive failures. When building with CONFIG_KUNIT, provide a failure path for all users of fortify_panic, and track whether the failure was a read overflow or a write overflow, for KUnit tests to examine. Inspired by similar logic in the slab tests. Signed-off-by: Kees Cook --- include/linux/fortify-string.h | 43 ++++++++++++++++++---------------- lib/fortify_kunit.c | 41 ++++++++++++++++++++++++++++++++ lib/string_helpers.c | 2 ++ 3 files changed, 66 insertions(+), 20 deletions(-) diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h index 4f6767dcd933..fbfb90479b8f 100644 --- a/include/linux/fortify-string.h +++ b/include/linux/fortify-string.h @@ -15,8 +15,10 @@ #define FORTIFY_REASON(func, write) (FIELD_PREP(BIT(0), write) | \ FIELD_PREP(GENMASK(7, 1), func)) -#define fortify_panic(func, write) \ - __fortify_panic(FORTIFY_REASON(func, write)) +#ifndef fortify_panic +# define fortify_panic(func, write, retfail) \ + __fortify_panic(FORTIFY_REASON(func, write)) +#endif #define FORTIFY_READ 0 #define FORTIFY_WRITE 1 @@ -181,7 +183,7 @@ char *strncpy(char * const POS p, const char *q, __kernel_size_t size) if (__compiletime_lessthan(p_size, size)) __write_overflow(); if (p_size < size) - fortify_panic(FORTIFY_FUNC_strncpy, FORTIFY_WRITE); + fortify_panic(FORTIFY_FUNC_strncpy, FORTIFY_WRITE, p); return __underlying_strncpy(p, q, size); } @@ -212,7 +214,7 @@ __FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size /* Do not check characters beyond the end of p. */ ret = __real_strnlen(p, maxlen < p_size ? maxlen : p_size); if (p_size <= ret && maxlen != ret) - fortify_panic(FORTIFY_FUNC_strnlen, FORTIFY_READ); + fortify_panic(FORTIFY_FUNC_strnlen, FORTIFY_READ, ret); return ret; } @@ -248,7 +250,7 @@ __kernel_size_t __fortify_strlen(const char * const POS p) return __underlying_strlen(p); ret = strnlen(p, p_size); if (p_size <= ret) - fortify_panic(FORTIFY_FUNC_strlen, FORTIFY_READ); + fortify_panic(FORTIFY_FUNC_strlen, FORTIFY_READ, ret); return ret; } @@ -299,7 +301,7 @@ __FORTIFY_INLINE ssize_t sized_strscpy(char * const POS p, const char * const PO * p_size. */ if (len > p_size) - fortify_panic(FORTIFY_FUNC_strscpy, FORTIFY_WRITE); + fortify_panic(FORTIFY_FUNC_strscpy, FORTIFY_WRITE, -E2BIG); /* * We can now safely call vanilla strscpy because we are protected from: @@ -357,7 +359,7 @@ size_t strlcat(char * const POS p, const char * const POS q, size_t avail) /* Give up if string is already overflowed. */ if (p_size <= p_len) - fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_READ); + fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_READ, wanted); if (actual >= avail) { copy_len = avail - p_len - 1; @@ -366,7 +368,7 @@ size_t strlcat(char * const POS p, const char * const POS q, size_t avail) /* Give up if copy will overflow. */ if (p_size <= actual) - fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_WRITE); + fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_WRITE, wanted); __underlying_memcpy(p + p_len, q, copy_len); p[actual] = '\0'; @@ -395,7 +397,7 @@ char *strcat(char * const POS p, const char *q) const size_t p_size = __member_size(p); if (strlcat(p, q, p_size) >= p_size) - fortify_panic(FORTIFY_FUNC_strcat, FORTIFY_WRITE); + fortify_panic(FORTIFY_FUNC_strcat, FORTIFY_WRITE, p); return p; } @@ -431,13 +433,13 @@ char *strncat(char * const POS p, const char * const POS q, __kernel_size_t coun p_len = strlen(p); copy_len = strnlen(q, count); if (p_size < p_len + copy_len + 1) - fortify_panic(FORTIFY_FUNC_strncat, FORTIFY_WRITE); + fortify_panic(FORTIFY_FUNC_strncat, FORTIFY_WRITE, p); __underlying_memcpy(p + p_len, q, copy_len); p[p_len + copy_len] = '\0'; return p; } -__FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size, +__FORTIFY_INLINE bool fortify_memset_chk(__kernel_size_t size, const size_t p_size, const size_t p_size_field) { @@ -472,7 +474,8 @@ __FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size, * lengths are unknown.) */ if (p_size != SIZE_MAX && p_size < size) - fortify_panic(FORTIFY_FUNC_memset, FORTIFY_WRITE); + fortify_panic(FORTIFY_FUNC_memset, FORTIFY_WRITE, true); + return false; } #define __fortify_memset_chk(p, c, size, p_size, p_size_field) ({ \ @@ -571,9 +574,9 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size, * lengths are unknown.) */ if (p_size != SIZE_MAX && p_size < size) - fortify_panic(func, FORTIFY_WRITE); + fortify_panic(func, FORTIFY_WRITE, true); else if (q_size != SIZE_MAX && q_size < size) - fortify_panic(func, FORTIFY_READ); + fortify_panic(func, FORTIFY_READ, true); /* * Warn when writing beyond destination field size. @@ -673,7 +676,7 @@ __FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size) if (__compiletime_lessthan(p_size, size)) __read_overflow(); if (p_size < size) - fortify_panic(FORTIFY_FUNC_memscan, FORTIFY_READ); + fortify_panic(FORTIFY_FUNC_memscan, FORTIFY_READ, NULL); return __real_memscan(p, c, size); } @@ -690,7 +693,7 @@ int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t __read_overflow2(); } if (p_size < size || q_size < size) - fortify_panic(FORTIFY_FUNC_memcmp, FORTIFY_READ); + fortify_panic(FORTIFY_FUNC_memcmp, FORTIFY_READ, INT_MIN); return __underlying_memcmp(p, q, size); } @@ -702,7 +705,7 @@ void *memchr(const void * const POS0 p, int c, __kernel_size_t size) if (__compiletime_lessthan(p_size, size)) __read_overflow(); if (p_size < size) - fortify_panic(FORTIFY_FUNC_memchr, FORTIFY_READ); + fortify_panic(FORTIFY_FUNC_memchr, FORTIFY_READ, NULL); return __underlying_memchr(p, c, size); } @@ -714,7 +717,7 @@ __FORTIFY_INLINE void *memchr_inv(const void * const POS0 p, int c, size_t size) if (__compiletime_lessthan(p_size, size)) __read_overflow(); if (p_size < size) - fortify_panic(FORTIFY_FUNC_memchr_inv, FORTIFY_READ); + fortify_panic(FORTIFY_FUNC_memchr_inv, FORTIFY_READ, NULL); return __real_memchr_inv(p, c, size); } @@ -727,7 +730,7 @@ __FORTIFY_INLINE void *kmemdup(const void * const POS0 p, size_t size, gfp_t gfp if (__compiletime_lessthan(p_size, size)) __read_overflow(); if (p_size < size) - fortify_panic(FORTIFY_FUNC_kmemdup, FORTIFY_READ); + fortify_panic(FORTIFY_FUNC_kmemdup, FORTIFY_READ, NULL); return __real_kmemdup(p, size, gfp); } @@ -764,7 +767,7 @@ char *strcpy(char * const POS p, const char * const POS q) __write_overflow(); /* Run-time check for dynamic size overflow. */ if (p_size < size) - fortify_panic(FORTIFY_FUNC_strcpy, FORTIFY_WRITE); + fortify_panic(FORTIFY_FUNC_strcpy, FORTIFY_WRITE, p); __underlying_memcpy(p, q, size); return p; } diff --git a/lib/fortify_kunit.c b/lib/fortify_kunit.c index 7a88b5dd3d27..4ba7d02fdd78 100644 --- a/lib/fortify_kunit.c +++ b/lib/fortify_kunit.c @@ -15,8 +15,17 @@ */ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt +/* Redefine fortify_panic() to track failures. */ +void fortify_add_kunit_error(int write); +#define fortify_panic(func, write, retfail) do { \ + __fortify_report(FORTIFY_REASON(func, write)); \ + fortify_add_kunit_error(write); \ + return (retfail); \ +} while (0) + #include #include +#include #include #include #include @@ -27,10 +36,34 @@ # define __compiletime_strlen __builtin_strlen #endif +static struct kunit_resource read_resource; +static struct kunit_resource write_resource; +static int fortify_read_overflows; +static int fortify_write_overflows; + static const char array_of_10[] = "this is 10"; static const char *ptr_of_11 = "this is 11!"; static char array_unknown[] = "compiler thinks I might change"; +void fortify_add_kunit_error(int write) +{ + struct kunit_resource *resource; + struct kunit *current_test; + + current_test = kunit_get_current_test(); + if (!current_test) + return; + + resource = kunit_find_named_resource(current_test, + write ? "fortify_write_overflows" + : "fortify_read_overflows"); + if (!resource) + return; + + (*(int *)resource->data)++; + kunit_put_resource(resource); +} + static void known_sizes_test(struct kunit *test) { KUNIT_EXPECT_EQ(test, __compiletime_strlen("88888888"), 8); @@ -318,6 +351,14 @@ static int fortify_test_init(struct kunit *test) if (!IS_ENABLED(CONFIG_FORTIFY_SOURCE)) kunit_skip(test, "Not built with CONFIG_FORTIFY_SOURCE=y"); + fortify_read_overflows = 0; + kunit_add_named_resource(test, NULL, NULL, &read_resource, + "fortify_read_overflows", + &fortify_read_overflows); + fortify_write_overflows = 0; + kunit_add_named_resource(test, NULL, NULL, &write_resource, + "fortify_write_overflows", + &fortify_write_overflows); return 0; } diff --git a/lib/string_helpers.c b/lib/string_helpers.c index 9291dc74ae01..5e53d42e32bb 100644 --- a/lib/string_helpers.c +++ b/lib/string_helpers.c @@ -18,6 +18,8 @@ #include #include #include +#include +#include /** * string_get_size - get the size in the specified units