diff options
Diffstat (limited to 'include/linux/fortify-string.h')
| -rw-r--r-- | include/linux/fortify-string.h | 245 |
1 files changed, 178 insertions, 67 deletions
diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h index 3b401fa0f374..b62c90cfafaf 100644 --- a/include/linux/fortify-string.h +++ b/include/linux/fortify-string.h @@ -2,7 +2,9 @@ #ifndef _LINUX_FORTIFY_STRING_H_ #define _LINUX_FORTIFY_STRING_H_ +#include <linux/bug.h> #include <linux/const.h> +#include <linux/limits.h> #define __FORTIFY_INLINE extern __always_inline __gnu_inline __overloadable #define __RENAME(x) __asm__(#x) @@ -17,9 +19,10 @@ void __write_overflow_field(size_t avail, size_t wanted) __compiletime_warning(" #define __compiletime_strlen(p) \ ({ \ unsigned char *__p = (unsigned char *)(p); \ - size_t __ret = (size_t)-1; \ - size_t __p_size = __builtin_object_size(p, 1); \ - if (__p_size != (size_t)-1) { \ + size_t __ret = SIZE_MAX; \ + size_t __p_size = __member_size(p); \ + if (__p_size != SIZE_MAX && \ + __builtin_constant_p(*__p)) { \ size_t __p_len = __p_size - 1; \ if (__builtin_constant_p(__p[__p_len]) && \ __p[__p_len] == '\0') \ @@ -69,20 +72,59 @@ extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) __underlying_memcpy(dst, src, bytes) /* - * Clang's use of __builtin_object_size() within inlines needs hinting via - * __pass_object_size(). The preference is to only ever use type 1 (member + * Clang's use of __builtin_*object_size() within inlines needs hinting via + * __pass_*object_size(). The preference is to only ever use type 1 (member * size, rather than struct size), but there remain some stragglers using * type 0 that will be converted in the future. */ -#define POS __pass_object_size(1) -#define POS0 __pass_object_size(0) +#define POS __pass_object_size(1) +#define POS0 __pass_object_size(0) +#define __struct_size(p) __builtin_object_size(p, 0) +#define __member_size(p) __builtin_object_size(p, 1) +#define __compiletime_lessthan(bounds, length) ( \ + __builtin_constant_p((bounds) < (length)) && \ + (bounds) < (length) \ +) + +/** + * strncpy - Copy a string to memory with non-guaranteed NUL padding + * + * @p: pointer to destination of copy + * @q: pointer to NUL-terminated source string to copy + * @size: bytes to write at @p + * + * If strlen(@q) >= @size, the copy of @q will stop after @size bytes, + * and @p will NOT be NUL-terminated + * + * If strlen(@q) < @size, following the copy of @q, trailing NUL bytes + * will be written to @p until @size total bytes have been written. + * + * Do not use this function. While FORTIFY_SOURCE tries to avoid + * over-reads of @q, it cannot defend against writing unterminated + * results to @p. Using strncpy() remains ambiguous and fragile. + * Instead, please choose an alternative, so that the expectation + * of @p's contents is unambiguous: + * + * +--------------------+-----------------+------------+ + * | @p needs to be: | padded to @size | not padded | + * +====================+=================+============+ + * | NUL-terminated | strscpy_pad() | strscpy() | + * +--------------------+-----------------+------------+ + * | not NUL-terminated | strtomem_pad() | strtomem() | + * +--------------------+-----------------+------------+ + * + * Note strscpy*()'s differing return values for detecting truncation, + * and strtomem*()'s expectation that the destination is marked with + * __nonstring when it is a character array. + * + */ __FORTIFY_INLINE __diagnose_as(__builtin_strncpy, 1, 2, 3) char *strncpy(char * const POS p, const char *q, __kernel_size_t size) { - size_t p_size = __builtin_object_size(p, 1); + size_t p_size = __member_size(p); - if (__builtin_constant_p(size) && p_size < size) + if (__compiletime_lessthan(p_size, size)) __write_overflow(); if (p_size < size) fortify_panic(__func__); @@ -92,9 +134,9 @@ char *strncpy(char * const POS p, const char *q, __kernel_size_t size) __FORTIFY_INLINE __diagnose_as(__builtin_strcat, 1, 2) char *strcat(char * const POS p, const char *q) { - size_t p_size = __builtin_object_size(p, 1); + size_t p_size = __member_size(p); - if (p_size == (size_t)-1) + if (p_size == SIZE_MAX) return __underlying_strcat(p, q); if (strlcat(p, q, p_size) >= p_size) fortify_panic(__func__); @@ -104,12 +146,12 @@ char *strcat(char * const POS p, const char *q) extern __kernel_size_t __real_strnlen(const char *, __kernel_size_t) __RENAME(strnlen); __FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size_t maxlen) { - size_t p_size = __builtin_object_size(p, 1); + size_t p_size = __member_size(p); size_t p_len = __compiletime_strlen(p); size_t ret; /* We can take compile-time actions when maxlen is const. */ - if (__builtin_constant_p(maxlen) && p_len != (size_t)-1) { + if (__builtin_constant_p(maxlen) && p_len != SIZE_MAX) { /* If p is const, we can use its compile-time-known len. */ if (maxlen >= p_size) return p_len; @@ -134,10 +176,10 @@ __FORTIFY_INLINE __diagnose_as(__builtin_strlen, 1) __kernel_size_t __fortify_strlen(const char * const POS p) { __kernel_size_t ret; - size_t p_size = __builtin_object_size(p, 1); + size_t p_size = __member_size(p); /* Give up if we don't know how large p is. */ - if (p_size == (size_t)-1) + if (p_size == SIZE_MAX) return __underlying_strlen(p); ret = strnlen(p, p_size); if (p_size <= ret) @@ -149,12 +191,12 @@ __kernel_size_t __fortify_strlen(const char * const POS p) extern size_t __real_strlcpy(char *, const char *, size_t) __RENAME(strlcpy); __FORTIFY_INLINE size_t strlcpy(char * const POS p, const char * const POS q, size_t size) { - size_t p_size = __builtin_object_size(p, 1); - size_t q_size = __builtin_object_size(q, 1); + size_t p_size = __member_size(p); + size_t q_size = __member_size(q); size_t q_len; /* Full count of source string length. */ size_t len; /* Count of characters going into destination. */ - if (p_size == (size_t)-1 && q_size == (size_t)-1) + if (p_size == SIZE_MAX && q_size == SIZE_MAX) return __real_strlcpy(p, q, size); q_len = strlen(q); len = (q_len >= size) ? size - 1 : q_len; @@ -178,18 +220,18 @@ __FORTIFY_INLINE ssize_t strscpy(char * const POS p, const char * const POS q, s { size_t len; /* Use string size rather than possible enclosing struct size. */ - size_t p_size = __builtin_object_size(p, 1); - size_t q_size = __builtin_object_size(q, 1); + size_t p_size = __member_size(p); + size_t q_size = __member_size(q); /* If we cannot get size of p and q default to call strscpy. */ - if (p_size == (size_t) -1 && q_size == (size_t) -1) + if (p_size == SIZE_MAX && q_size == SIZE_MAX) return __real_strscpy(p, q, size); /* * If size can be known at compile time and is greater than * p_size, generate a compile time write overflow error. */ - if (__builtin_constant_p(size) && size > p_size) + if (__compiletime_lessthan(p_size, size)) __write_overflow(); /* @@ -224,10 +266,10 @@ __FORTIFY_INLINE __diagnose_as(__builtin_strncat, 1, 2, 3) char *strncat(char * const POS p, const char * const POS q, __kernel_size_t count) { size_t p_len, copy_len; - size_t p_size = __builtin_object_size(p, 1); - size_t q_size = __builtin_object_size(q, 1); + size_t p_size = __member_size(p); + size_t q_size = __member_size(q); - if (p_size == (size_t)-1 && q_size == (size_t)-1) + if (p_size == SIZE_MAX && q_size == SIZE_MAX) return __underlying_strncat(p, q, count); p_len = strlen(p); copy_len = strnlen(q, count); @@ -246,15 +288,16 @@ __FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size, /* * Length argument is a constant expression, so we * can perform compile-time bounds checking where - * buffer sizes are known. + * buffer sizes are also known at compile time. */ /* Error when size is larger than enclosing struct. */ - if (p_size > p_size_field && p_size < size) + if (__compiletime_lessthan(p_size_field, p_size) && + __compiletime_lessthan(p_size, size)) __write_overflow(); /* Warn when write size is larger than dest field. */ - if (p_size_field < size) + if (__compiletime_lessthan(p_size_field, size)) __write_overflow_field(p_size_field, size); } /* @@ -268,10 +311,10 @@ __FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size, /* * Always stop accesses beyond the struct that contains the * field, when the buffer's remaining size is known. - * (The -1 test is to optimize away checks where the buffer + * (The SIZE_MAX test is to optimize away checks where the buffer * lengths are unknown.) */ - if (p_size != (size_t)(-1) && p_size < size) + if (p_size != SIZE_MAX && p_size < size) fortify_panic("memset"); } @@ -282,11 +325,11 @@ __FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size, }) /* - * __builtin_object_size() must be captured here to avoid evaluating argument - * side-effects further into the macro layers. + * __struct_size() vs __member_size() must be captured here to avoid + * evaluating argument side-effects further into the macro layers. */ #define memset(p, c, s) __fortify_memset_chk(p, c, s, \ - __builtin_object_size(p, 0), __builtin_object_size(p, 1)) + __struct_size(p), __member_size(p)) /* * To make sure the compiler can enforce protection against buffer overflows, @@ -319,7 +362,7 @@ __FORTIFY_INLINE void fortify_memset_chk(__kernel_size_t size, * V = vulnerable to run-time overflow (will need refactoring to solve) * */ -__FORTIFY_INLINE void fortify_memcpy_chk(__kernel_size_t size, +__FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size, const size_t p_size, const size_t q_size, const size_t p_size_field, @@ -330,25 +373,28 @@ __FORTIFY_INLINE void fortify_memcpy_chk(__kernel_size_t size, /* * Length argument is a constant expression, so we * can perform compile-time bounds checking where - * buffer sizes are known. + * buffer sizes are also known at compile time. */ /* Error when size is larger than enclosing struct. */ - if (p_size > p_size_field && p_size < size) + if (__compiletime_lessthan(p_size_field, p_size) && + __compiletime_lessthan(p_size, size)) __write_overflow(); - if (q_size > q_size_field && q_size < size) + if (__compiletime_lessthan(q_size_field, q_size) && + __compiletime_lessthan(q_size, size)) __read_overflow2(); /* Warn when write size argument larger than dest field. */ - if (p_size_field < size) + if (__compiletime_lessthan(p_size_field, size)) __write_overflow_field(p_size_field, size); /* * Warn for source field over-read when building with W=1 * or when an over-write happened, so both can be fixed at * the same time. */ - if ((IS_ENABLED(KBUILD_EXTRA_WARN1) || p_size_field < size) && - q_size_field < size) + if ((IS_ENABLED(KBUILD_EXTRA_WARN1) || + __compiletime_lessthan(p_size_field, size)) && + __compiletime_lessthan(q_size_field, size)) __read_overflow2_field(q_size_field, size); } /* @@ -362,41 +408,104 @@ __FORTIFY_INLINE void fortify_memcpy_chk(__kernel_size_t size, /* * Always stop accesses beyond the struct that contains the * field, when the buffer's remaining size is known. - * (The -1 test is to optimize away checks where the buffer + * (The SIZE_MAX test is to optimize away checks where the buffer * lengths are unknown.) */ - if ((p_size != (size_t)(-1) && p_size < size) || - (q_size != (size_t)(-1) && q_size < size)) + if ((p_size != SIZE_MAX && p_size < size) || + (q_size != SIZE_MAX && q_size < size)) fortify_panic(func); + + /* + * Warn when writing beyond destination field size. + * + * We must ignore p_size_field == 0 for existing 0-element + * fake flexible arrays, until they are all converted to + * proper flexible arrays. + * + * The implementation of __builtin_*object_size() behaves + * like sizeof() when not directly referencing a flexible + * array member, which means there will be many bounds checks + * that will appear at run-time, without a way for them to be + * detected at compile-time (as can be done when the destination + * is specifically the flexible array member). + * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101832 + */ + if (p_size_field != 0 && p_size_field != SIZE_MAX && + p_size != p_size_field && p_size_field < size) + return true; + + return false; } #define __fortify_memcpy_chk(p, q, size, p_size, q_size, \ p_size_field, q_size_field, op) ({ \ size_t __fortify_size = (size_t)(size); \ - fortify_memcpy_chk(__fortify_size, p_size, q_size, \ - p_size_field, q_size_field, #op); \ + WARN_ONCE(fortify_memcpy_chk(__fortify_size, p_size, q_size, \ + p_size_field, q_size_field, #op), \ + #op ": detected field-spanning write (size %zu) of single %s (size %zu)\n", \ + __fortify_size, \ + "field \"" #p "\" at " __FILE__ ":" __stringify(__LINE__), \ + p_size_field); \ __underlying_##op(p, q, __fortify_size); \ }) /* - * __builtin_object_size() must be captured here to avoid evaluating argument - * side-effects further into the macro layers. + * Notes about compile-time buffer size detection: + * + * With these types... + * + * struct middle { + * u16 a; + * u8 middle_buf[16]; + * int b; + * }; + * struct end { + * u16 a; + * u8 end_buf[16]; + * }; + * struct flex { + * int a; + * u8 flex_buf[]; + * }; + * + * void func(TYPE *ptr) { ... } + * + * Cases where destination size cannot be currently detected: + * - the size of ptr's object (seemingly by design, gcc & clang fail): + * __builtin_object_size(ptr, 1) == SIZE_MAX + * - the size of flexible arrays in ptr's obj (by design, dynamic size): + * __builtin_object_size(ptr->flex_buf, 1) == SIZE_MAX + * - the size of ANY array at the end of ptr's obj (gcc and clang bug): + * __builtin_object_size(ptr->end_buf, 1) == SIZE_MAX + * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101836 + * + * Cases where destination size is currently detected: + * - the size of non-array members within ptr's object: + * __builtin_object_size(ptr->a, 1) == 2 + * - the size of non-flexible-array in the middle of ptr's obj: + * __builtin_object_size(ptr->middle_buf, 1) == 16 + * + */ + +/* + * __struct_size() vs __member_size() must be captured here to avoid + * evaluating argument side-effects further into the macro layers. */ #define memcpy(p, q, s) __fortify_memcpy_chk(p, q, s, \ - __builtin_object_size(p, 0), __builtin_object_size(q, 0), \ - __builtin_object_size(p, 1), __builtin_object_size(q, 1), \ + __struct_size(p), __struct_size(q), \ + __member_size(p), __member_size(q), \ memcpy) #define memmove(p, q, s) __fortify_memcpy_chk(p, q, s, \ - __builtin_object_size(p, 0), __builtin_object_size(q, 0), \ - __builtin_object_size(p, 1), __builtin_object_size(q, 1), \ + __struct_size(p), __struct_size(q), \ + __member_size(p), __member_size(q), \ memmove) extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan); __FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size) { - size_t p_size = __builtin_object_size(p, 0); + size_t p_size = __struct_size(p); - if (__builtin_constant_p(size) && p_size < size) + if (__compiletime_lessthan(p_size, size)) __read_overflow(); if (p_size < size) fortify_panic(__func__); @@ -406,13 +515,13 @@ __FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size) __FORTIFY_INLINE __diagnose_as(__builtin_memcmp, 1, 2, 3) int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t size) { - size_t p_size = __builtin_object_size(p, 0); - size_t q_size = __builtin_object_size(q, 0); + size_t p_size = __struct_size(p); + size_t q_size = __struct_size(q); if (__builtin_constant_p(size)) { - if (p_size < size) + if (__compiletime_lessthan(p_size, size)) __read_overflow(); - if (q_size < size) + if (__compiletime_lessthan(q_size, size)) __read_overflow2(); } if (p_size < size || q_size < size) @@ -423,9 +532,9 @@ int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t __FORTIFY_INLINE __diagnose_as(__builtin_memchr, 1, 2, 3) void *memchr(const void * const POS0 p, int c, __kernel_size_t size) { - size_t p_size = __builtin_object_size(p, 0); + size_t p_size = __struct_size(p); - if (__builtin_constant_p(size) && p_size < size) + if (__compiletime_lessthan(p_size, size)) __read_overflow(); if (p_size < size) fortify_panic(__func__); @@ -435,9 +544,9 @@ void *memchr(const void * const POS0 p, int c, __kernel_size_t size) void *__real_memchr_inv(const void *s, int c, size_t n) __RENAME(memchr_inv); __FORTIFY_INLINE void *memchr_inv(const void * const POS0 p, int c, size_t size) { - size_t p_size = __builtin_object_size(p, 0); + size_t p_size = __struct_size(p); - if (__builtin_constant_p(size) && p_size < size) + if (__compiletime_lessthan(p_size, size)) __read_overflow(); if (p_size < size) fortify_panic(__func__); @@ -447,9 +556,9 @@ __FORTIFY_INLINE void *memchr_inv(const void * const POS0 p, int c, size_t size) extern void *__real_kmemdup(const void *src, size_t len, gfp_t gfp) __RENAME(kmemdup); __FORTIFY_INLINE void *kmemdup(const void * const POS0 p, size_t size, gfp_t gfp) { - size_t p_size = __builtin_object_size(p, 0); + size_t p_size = __struct_size(p); - if (__builtin_constant_p(size) && p_size < size) + if (__compiletime_lessthan(p_size, size)) __read_overflow(); if (p_size < size) fortify_panic(__func__); @@ -460,16 +569,18 @@ __FORTIFY_INLINE void *kmemdup(const void * const POS0 p, size_t size, gfp_t gfp __FORTIFY_INLINE __diagnose_as(__builtin_strcpy, 1, 2) char *strcpy(char * const POS p, const char * const POS q) { - size_t p_size = __builtin_object_size(p, 1); - size_t q_size = __builtin_object_size(q, 1); + size_t p_size = __member_size(p); + size_t q_size = __member_size(q); size_t size; /* If neither buffer size is known, immediately give up. */ - if (p_size == (size_t)-1 && q_size == (size_t)-1) + if (__builtin_constant_p(p_size) && + __builtin_constant_p(q_size) && + p_size == SIZE_MAX && q_size == SIZE_MAX) return __underlying_strcpy(p, q); size = strlen(q) + 1; /* Compile-time check for const size overflow. */ - if (__builtin_constant_p(size) && p_size < size) + if (__compiletime_lessthan(p_size, size)) __write_overflow(); /* Run-time check for dynamic size overflow. */ if (p_size < size) |