Improve the reporting of buffer overflows under CONFIG_FORTIFY_SOURCE to help accelerate debugging efforts. The calculations are all just sitting in registers anyway, so pass them along to the function to be reported.
For example, before: detected buffer overflow in memcpy and after: memcpy: detected buffer overflow: 4096 byte read of buffer size 1 Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Kees Cook <[email protected]> --- arch/arm/boot/compressed/misc.c | 2 +- arch/x86/boot/compressed/misc.c | 2 +- include/linux/fortify-string.h | 56 ++++++++++++++++++--------------- lib/fortify_kunit.c | 4 +-- lib/string_helpers.c | 9 +++--- 5 files changed, 39 insertions(+), 34 deletions(-) diff --git a/arch/arm/boot/compressed/misc.c b/arch/arm/boot/compressed/misc.c index d93e2e466f6a..6c41b270560e 100644 --- a/arch/arm/boot/compressed/misc.c +++ b/arch/arm/boot/compressed/misc.c @@ -154,7 +154,7 @@ decompress_kernel(unsigned long output_start, unsigned long free_mem_ptr_p, putstr(" done, booting the kernel.\n"); } -void __fortify_panic(const u8 reason) +void __fortify_panic(const u8 reason, size_t avail, size_t size) { error("detected buffer overflow"); } diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c index c9971b9dbb09..1844da203da9 100644 --- a/arch/x86/boot/compressed/misc.c +++ b/arch/x86/boot/compressed/misc.c @@ -496,7 +496,7 @@ asmlinkage __visible void *extract_kernel(void *rmode, unsigned char *output) return output + entry_offset; } -void __fortify_panic(const u8 reason) +void __fortify_panic(const u8 reason, size_t avail, size_t size) { error("detected buffer overflow"); } diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h index fbfb90479b8f..6aeebe0a6777 100644 --- a/include/linux/fortify-string.h +++ b/include/linux/fortify-string.h @@ -16,8 +16,8 @@ FIELD_PREP(GENMASK(7, 1), func)) #ifndef fortify_panic -# define fortify_panic(func, write, retfail) \ - __fortify_panic(FORTIFY_REASON(func, write)) +# define fortify_panic(func, write, avail, size, retfail) \ + __fortify_panic(FORTIFY_REASON(func, write), avail, size) #endif #define FORTIFY_READ 0 @@ -48,8 +48,8 @@ enum fortify_func { EACH_FORTIFY_FUNC(MAKE_FORTIFY_FUNC) }; -void __fortify_report(const u8 reason); -void __fortify_panic(const u8 reason) __cold __noreturn; +void __fortify_report(const u8 reason, const size_t avail, const size_t size); +void __fortify_panic(const u8 reason, const size_t avail, const size_t size) __cold __noreturn; void __read_overflow(void) __compiletime_error("detected read beyond size of object (1st parameter)"); void __read_overflow2(void) __compiletime_error("detected read beyond size of object (2nd parameter)"); void __read_overflow2_field(size_t avail, size_t wanted) __compiletime_warning("detected read beyond size of field (2nd parameter); maybe use struct_group()?"); @@ -183,7 +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, p); + fortify_panic(FORTIFY_FUNC_strncpy, FORTIFY_WRITE, p_size, size, p); return __underlying_strncpy(p, q, size); } @@ -214,7 +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, ret); + fortify_panic(FORTIFY_FUNC_strnlen, FORTIFY_READ, p_size, ret + 1, ret); return ret; } @@ -250,7 +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, ret); + fortify_panic(FORTIFY_FUNC_strlen, FORTIFY_READ, p_size, ret + 1, ret); return ret; } @@ -300,8 +300,8 @@ __FORTIFY_INLINE ssize_t sized_strscpy(char * const POS p, const char * const PO * Generate a runtime write overflow error if len is greater than * p_size. */ - if (len > p_size) - fortify_panic(FORTIFY_FUNC_strscpy, FORTIFY_WRITE, -E2BIG); + if (p_size < len) + fortify_panic(FORTIFY_FUNC_strscpy, FORTIFY_WRITE, p_size, len, -E2BIG); /* * We can now safely call vanilla strscpy because we are protected from: @@ -359,7 +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, wanted); + fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_READ, p_size, p_len + 1, wanted); if (actual >= avail) { copy_len = avail - p_len - 1; @@ -368,7 +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, wanted); + fortify_panic(FORTIFY_FUNC_strlcat, FORTIFY_WRITE, p_size, actual + 1, wanted); __underlying_memcpy(p + p_len, q, copy_len); p[actual] = '\0'; @@ -395,9 +395,10 @@ __FORTIFY_INLINE __diagnose_as(__builtin_strcat, 1, 2) char *strcat(char * const POS p, const char *q) { const size_t p_size = __member_size(p); + const size_t wanted = strlcat(p, q, p_size); - if (strlcat(p, q, p_size) >= p_size) - fortify_panic(FORTIFY_FUNC_strcat, FORTIFY_WRITE, p); + if (p_size <= wanted) + fortify_panic(FORTIFY_FUNC_strcat, FORTIFY_WRITE, p_size, wanted + 1, p); return p; } @@ -426,14 +427,15 @@ char *strncat(char * const POS p, const char * const POS q, __kernel_size_t coun { const size_t p_size = __member_size(p); const size_t q_size = __member_size(q); - size_t p_len, copy_len; + size_t p_len, copy_len, total; if (p_size == SIZE_MAX && q_size == SIZE_MAX) 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(FORTIFY_FUNC_strncat, FORTIFY_WRITE, p); + total = p_len + copy_len + 1; + if (p_size < total) + fortify_panic(FORTIFY_FUNC_strncat, FORTIFY_WRITE, p_size, total, p); __underlying_memcpy(p + p_len, q, copy_len); p[p_len + copy_len] = '\0'; return p; @@ -474,7 +476,7 @@ __FORTIFY_INLINE bool 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, true); + fortify_panic(FORTIFY_FUNC_memset, FORTIFY_WRITE, p_size, size, true); return false; } @@ -574,9 +576,9 @@ __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, true); + fortify_panic(func, FORTIFY_WRITE, p_size, size, true); else if (q_size != SIZE_MAX && q_size < size) - fortify_panic(func, FORTIFY_READ, true); + fortify_panic(func, FORTIFY_READ, p_size, size, true); /* * Warn when writing beyond destination field size. @@ -676,7 +678,7 @@ __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, NULL); + fortify_panic(FORTIFY_FUNC_memscan, FORTIFY_READ, p_size, size, NULL); return __real_memscan(p, c, size); } @@ -692,8 +694,10 @@ int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t if (__compiletime_lessthan(q_size, size)) __read_overflow2(); } - if (p_size < size || q_size < size) - fortify_panic(FORTIFY_FUNC_memcmp, FORTIFY_READ, INT_MIN); + if (p_size < size) + fortify_panic(FORTIFY_FUNC_memcmp, FORTIFY_READ, p_size, size, INT_MIN); + else if (q_size < size) + fortify_panic(FORTIFY_FUNC_memcmp, FORTIFY_READ, q_size, size, INT_MIN); return __underlying_memcmp(p, q, size); } @@ -705,7 +709,7 @@ 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, NULL); + fortify_panic(FORTIFY_FUNC_memchr, FORTIFY_READ, p_size, size, NULL); return __underlying_memchr(p, c, size); } @@ -717,7 +721,7 @@ __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, NULL); + fortify_panic(FORTIFY_FUNC_memchr_inv, FORTIFY_READ, p_size, size, NULL); return __real_memchr_inv(p, c, size); } @@ -730,7 +734,7 @@ __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, NULL); + fortify_panic(FORTIFY_FUNC_kmemdup, FORTIFY_READ, p_size, size, NULL); return __real_kmemdup(p, size, gfp); } @@ -767,7 +771,7 @@ 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, p); + fortify_panic(FORTIFY_FUNC_strcpy, FORTIFY_WRITE, p_size, size, p); __underlying_memcpy(p, q, size); return p; } diff --git a/lib/fortify_kunit.c b/lib/fortify_kunit.c index f0accebeca02..493ec02dd5b3 100644 --- a/lib/fortify_kunit.c +++ b/lib/fortify_kunit.c @@ -17,8 +17,8 @@ /* 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)); \ +#define fortify_panic(func, write, avail, size, retfail) do { \ + __fortify_report(FORTIFY_REASON(func, write), avail, size); \ fortify_add_kunit_error(write); \ return (retfail); \ } while (0) diff --git a/lib/string_helpers.c b/lib/string_helpers.c index 5e53d42e32bb..5419282e12bd 100644 --- a/lib/string_helpers.c +++ b/lib/string_helpers.c @@ -1016,20 +1016,21 @@ static const char * const fortify_func_name[] = { #undef MAKE_FORTIFY_FUNC_NAME }; -void __fortify_report(const u8 reason) +void __fortify_report(const u8 reason, const size_t avail, const size_t size) { const u8 func = FORTIFY_REASON_FUNC(reason); const bool write = FORTIFY_REASON_DIR(reason); const char *name; name = fortify_func_name[umin(func, FORTIFY_FUNC_UNKNOWN)]; - WARN(1, "%s: detected buffer %s overflow\n", name, str_read_write(!write)); + WARN(1, "%s: detected buffer overflow: %zu byte %s of buffer size %zu\n", + name, size, str_read_write(!write), avail); } EXPORT_SYMBOL(__fortify_report); -void __fortify_panic(const u8 reason) +void __fortify_panic(const u8 reason, const size_t avail, const size_t size) { - __fortify_report(reason); + __fortify_report(reason, avail, size); BUG(); } EXPORT_SYMBOL(__fortify_panic); -- 2.34.1
