reallocarray() is a safer variant of realloc which checks for multiplication overflow in case of array allocation. Since it's not available in Glibc < 2.26 import kernel's overflow.h and add a static inline implementation when needed. Use feature detection to probe for existence of reallocarray.
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| @@ -36,3 +36,7 @@ · 35 unmodified lines | ||
| 36 | 36 | #endif |
| 37 | 37 | #define __printf(a, b) __attribute__((format(printf, a, b))) |
| 38 | 38 | #define __scanf(a, b) __attribute__((format(scanf, a, b))) |
| 39 | + | |
| 40 | +#if GCC_VERSION >= 50100 | |
| 41 | +#define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1 | |
| 42 | +#endif | |
| @@ -0,0 +1,278 @@ | ||
| 1 | +/* SPDX-License-Identifier: GPL-2.0 OR MIT */ | |
| 2 | +#ifndef __LINUX_OVERFLOW_H | |
| 3 | +#define __LINUX_OVERFLOW_H | |
| 4 | + | |
| 5 | +#include <linux/compiler.h> | |
| 6 | + | |
| 7 | +/* | |
| 8 | + * In the fallback code below, we need to compute the minimum and | |
| 9 | + * maximum values representable in a given type. These macros may also | |
| 10 | + * be useful elsewhere, so we provide them outside the | |
| 11 | + * COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW block. | |
| 12 | + * | |
| 13 | + * It would seem more obvious to do something like | |
| 14 | + * | |
| 15 | + * #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0) | |
| 16 | + * #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0) | |
| 17 | + * | |
| 18 | + * Unfortunately, the middle expressions, strictly speaking, have | |
| 19 | + * undefined behaviour, and at least some versions of gcc warn about | |
| 20 | + * the type_max expression (but not if -fsanitize=undefined is in | |
| 21 | + * effect; in that case, the warning is deferred to runtime...). | |
| 22 | + * | |
| 23 | + * The slightly excessive casting in type_min is to make sure the | |
| 24 | + * macros also produce sensible values for the exotic type _Bool. [The | |
| 25 | + * overflow checkers only almost work for _Bool, but that's | |
| 26 | + * a-feature-not-a-bug, since people shouldn't be doing arithmetic on | |
| 27 | + * _Bools. Besides, the gcc builtins don't allow _Bool* as third | |
| 28 | + * argument.] | |
| 29 | + * | |
| 30 | + * Idea stolen from | |
| 31 | + * https://mail-index.netbsd.org/tech-misc/2007/02/05/0000.html - | |
| 32 | + * credit to Christian Biere. | |
| 33 | + */ | |
| 34 | +#define is_signed_type(type) (((type)(-1)) < (type)1) | |
| 35 | +#define __type_half_max(type) ((type)1 << (8*sizeof(type) - 1 - is_signed_type(type))) | |
| 36 | +#define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T))) | |
| 37 | +#define type_min(T) ((T)((T)-type_max(T)-(T)1)) | |
| 38 | + | |
| 39 | + | |
| 40 | +#ifdef COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW | |
| 41 | +/* | |
| 42 | + * For simplicity and code hygiene, the fallback code below insists on | |
| 43 | + * a, b and *d having the same type (similar to the min() and max() | |
| 44 | + * macros), whereas gcc's type-generic overflow checkers accept | |
| 45 | + * different types. Hence we don't just make check_add_overflow an | |
| 46 | + * alias for __builtin_add_overflow, but add type checks similar to | |
| 47 | + * below. | |
| 48 | + */ | |
| 49 | +#define check_add_overflow(a, b, d) ({ \ | |
| 50 | + typeof(a) __a = (a); \ | |
| 51 | + typeof(b) __b = (b); \ | |
| 52 | + typeof(d) __d = (d); \ | |
| 53 | + (void) (&__a == &__b); \ | |
| 54 | + (void) (&__a == __d); \ | |
| 55 | + __builtin_add_overflow(__a, __b, __d); \ | |
| 56 | +}) | |
| 57 | + | |
| 58 | +#define check_sub_overflow(a, b, d) ({ \ | |
| 59 | + typeof(a) __a = (a); \ | |
| 60 | + typeof(b) __b = (b); \ | |
| 61 | + typeof(d) __d = (d); \ | |
| 62 | + (void) (&__a == &__b); \ | |
| 63 | + (void) (&__a == __d); \ | |
| 64 | + __builtin_sub_overflow(__a, __b, __d); \ | |
| 65 | +}) | |
| 66 | + | |
| 67 | +#define check_mul_overflow(a, b, d) ({ \ | |
| 68 | + typeof(a) __a = (a); \ | |
| 69 | + typeof(b) __b = (b); \ | |
| 70 | + typeof(d) __d = (d); \ | |
| 71 | + (void) (&__a == &__b); \ | |
| 72 | + (void) (&__a == __d); \ | |
| 73 | + __builtin_mul_overflow(__a, __b, __d); \ | |
| 74 | +}) | |
| 75 | + | |
| 76 | +#else | |
| 77 | + | |
| 78 | + | |
| 79 | +/* Checking for unsigned overflow is relatively easy without causing UB. */ | |
| 80 | +#define __unsigned_add_overflow(a, b, d) ({ \ | |
| 81 | + typeof(a) __a = (a); \ | |
| 82 | + typeof(b) __b = (b); \ | |
| 83 | + typeof(d) __d = (d); \ | |
| 84 | + (void) (&__a == &__b); \ | |
| 85 | + (void) (&__a == __d); \ | |
| 86 | + *__d = __a + __b; \ | |
| 87 | + *__d < __a; \ | |
| 88 | +}) | |
| 89 | +#define __unsigned_sub_overflow(a, b, d) ({ \ | |
| 90 | + typeof(a) __a = (a); \ | |
| 91 | + typeof(b) __b = (b); \ | |
| 92 | + typeof(d) __d = (d); \ | |
| 93 | + (void) (&__a == &__b); \ | |
| 94 | + (void) (&__a == __d); \ | |
| 95 | + *__d = __a - __b; \ | |
| 96 | + __a < __b; \ | |
| 97 | +}) | |
| 98 | +/* | |
| 99 | + * If one of a or b is a compile-time constant, this avoids a division. | |
| 100 | + */ | |
| 101 | +#define __unsigned_mul_overflow(a, b, d) ({ \ | |
| 102 | + typeof(a) __a = (a); \ | |
| 103 | + typeof(b) __b = (b); \ | |
| 104 | + typeof(d) __d = (d); \ | |
| 105 | + (void) (&__a == &__b); \ | |
| 106 | + (void) (&__a == __d); \ | |
| 107 | + *__d = __a * __b; \ | |
| 108 | + __builtin_constant_p(__b) ? \ | |
| 109 | + __b > 0 && __a > type_max(typeof(__a)) / __b : \ | |
| 110 | + __a > 0 && __b > type_max(typeof(__b)) / __a; \ | |
| 111 | +}) | |
| 112 | + | |
| 113 | +/* | |
| 114 | + * For signed types, detecting overflow is much harder, especially if | |
| 115 | + * we want to avoid UB. But the interface of these macros is such that | |
| 116 | + * we must provide a result in *d, and in fact we must produce the | |
| 117 | + * result promised by gcc's builtins, which is simply the possibly | |
| 118 | + * wrapped-around value. Fortunately, we can just formally do the | |
| 119 | + * operations in the widest relevant unsigned type (u64) and then | |
| 120 | + * truncate the result - gcc is smart enough to generate the same code | |
| 121 | + * with and without the (u64) casts. | |
| 122 | + */ | |
| 123 | + | |
| 124 | +/* | |
| 125 | + * Adding two signed integers can overflow only if they have the same | |
| 126 | + * sign, and overflow has happened iff the result has the opposite | |
| 127 | + * sign. | |
| 128 | + */ | |
| 129 | +#define __signed_add_overflow(a, b, d) ({ \ | |
| 130 | + typeof(a) __a = (a); \ | |
| 131 | + typeof(b) __b = (b); \ | |
| 132 | + typeof(d) __d = (d); \ | |
| 133 | + (void) (&__a == &__b); \ | |
| 134 | + (void) (&__a == __d); \ | |
| 135 | + *__d = (u64)__a + (u64)__b; \ | |
| 136 | + (((~(__a ^ __b)) & (*__d ^ __a)) \ | |
| 137 | + & type_min(typeof(__a))) != 0; \ | |
| 138 | +}) | |
| 139 | + | |
| 140 | +/* | |
| 141 | + * Subtraction is similar, except that overflow can now happen only | |
| 142 | + * when the signs are opposite. In this case, overflow has happened if | |
| 143 | + * the result has the opposite sign of a. | |
| 144 | + */ | |
| 145 | +#define __signed_sub_overflow(a, b, d) ({ \ | |
| 146 | + typeof(a) __a = (a); \ | |
| 147 | + typeof(b) __b = (b); \ | |
| 148 | + typeof(d) __d = (d); \ | |
| 149 | + (void) (&__a == &__b); \ | |
| 150 | + (void) (&__a == __d); \ | |
| 151 | + *__d = (u64)__a - (u64)__b; \ | |
| 152 | + ((((__a ^ __b)) & (*__d ^ __a)) \ | |
| 153 | + & type_min(typeof(__a))) != 0; \ | |
| 154 | +}) | |
| 155 | + | |
| 156 | +/* | |
| 157 | + * Signed multiplication is rather hard. gcc always follows C99, so | |
| 158 | + * division is truncated towards 0. This means that we can write the | |
| 159 | + * overflow check like this: | |
| 160 | + * | |
| 161 | + * (a > 0 && (b > MAX/a || b < MIN/a)) || | |
| 162 | + * (a < -1 && (b > MIN/a || b < MAX/a) || | |
| 163 | + * (a == -1 && b == MIN) | |
| 164 | + * | |
| 165 | + * The redundant casts of -1 are to silence an annoying -Wtype-limits | |
| 166 | + * (included in -Wextra) warning: When the type is u8 or u16, the | |
| 167 | + * __b_c_e in check_mul_overflow obviously selects | |
| 168 | + * __unsigned_mul_overflow, but unfortunately gcc still parses this | |
| 169 | + * code and warns about the limited range of __b. | |
| 170 | + */ | |
| 171 | + | |
| 172 | +#define __signed_mul_overflow(a, b, d) ({ \ | |
| 173 | + typeof(a) __a = (a); \ | |
| 174 | + typeof(b) __b = (b); \ | |
| 175 | + typeof(d) __d = (d); \ | |
| 176 | + typeof(a) __tmax = type_max(typeof(a)); \ | |
| 177 | + typeof(a) __tmin = type_min(typeof(a)); \ | |
| 178 | + (void) (&__a == &__b); \ | |
| 179 | + (void) (&__a == __d); \ | |
| 180 | + *__d = (u64)__a * (u64)__b; \ | |
| 181 | + (__b > 0 && (__a > __tmax/__b || __a < __tmin/__b)) || \ | |
| 182 | + (__b < (typeof(__b))-1 && (__a > __tmin/__b || __a < __tmax/__b)) || \ | |
| 183 | + (__b == (typeof(__b))-1 && __a == __tmin); \ | |
| 184 | +}) | |
| 185 | + | |
| 186 | + | |
| 187 | +#define check_add_overflow(a, b, d) \ | |
| 188 | + __builtin_choose_expr(is_signed_type(typeof(a)), \ | |
| 189 | + __signed_add_overflow(a, b, d), \ | |
| 190 | + __unsigned_add_overflow(a, b, d)) | |
| 191 | + | |
| 192 | +#define check_sub_overflow(a, b, d) \ | |
| 193 | + __builtin_choose_expr(is_signed_type(typeof(a)), \ | |
| 194 | + __signed_sub_overflow(a, b, d), \ | |
| 195 | + __unsigned_sub_overflow(a, b, d)) | |
| 196 | + | |
| 197 | +#define check_mul_overflow(a, b, d) \ | |
| 198 | + __builtin_choose_expr(is_signed_type(typeof(a)), \ | |
| 199 | + __signed_mul_overflow(a, b, d), \ | |
| 200 | + __unsigned_mul_overflow(a, b, d)) | |
| 201 | + | |
| 202 | + | |
| 203 | +#endif /* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */ | |
| 204 | + | |
| 205 | +/** | |
| 206 | + * array_size() - Calculate size of 2-dimensional array. | |
| 207 | + * | |
| 208 | + * @a: dimension one | |
| 209 | + * @b: dimension two | |
| 210 | + * | |
| 211 | + * Calculates size of 2-dimensional array: @a * @b. | |
| 212 | + * | |
| 213 | + * Returns: number of bytes needed to represent the array or SIZE_MAX on | |
| 214 | + * overflow. | |
| 215 | + */ | |
| 216 | +static inline __must_check size_t array_size(size_t a, size_t b) | |
| 217 | +{ | |
| 218 | + size_t bytes; | |
| 219 | + | |
| 220 | + if (check_mul_overflow(a, b, &bytes)) | |
| 221 | + return SIZE_MAX; | |
| 222 | + | |
| 223 | + return bytes; | |
| 224 | +} | |
| 225 | + | |
| 226 | +/** | |
| 227 | + * array3_size() - Calculate size of 3-dimensional array. | |
| 228 | + * | |
| 229 | + * @a: dimension one | |
| 230 | + * @b: dimension two | |
| 231 | + * @c: dimension three | |
| 232 | + * | |
| 233 | + * Calculates size of 3-dimensional array: @a * @b * @c. | |
| 234 | + * | |
| 235 | + * Returns: number of bytes needed to represent the array or SIZE_MAX on | |
| 236 | + * overflow. | |
| 237 | + */ | |
| 238 | +static inline __must_check size_t array3_size(size_t a, size_t b, size_t c) | |
| 239 | +{ | |
| 240 | + size_t bytes; | |
| 241 | + | |
| 242 | + if (check_mul_overflow(a, b, &bytes)) | |
| 243 | + return SIZE_MAX; | |
| 244 | + if (check_mul_overflow(bytes, c, &bytes)) | |
| 245 | + return SIZE_MAX; | |
| 246 | + | |
| 247 | + return bytes; | |
| 248 | +} | |
| 249 | + | |
| 250 | +static inline __must_check size_t __ab_c_size(size_t n, size_t size, size_t c) | |
| 251 | +{ | |
| 252 | + size_t bytes; | |
| 253 | + | |
| 254 | + if (check_mul_overflow(n, size, &bytes)) | |
| 255 | + return SIZE_MAX; | |
| 256 | + if (check_add_overflow(bytes, c, &bytes)) | |
| 257 | + return SIZE_MAX; | |
| 258 | + | |
| 259 | + return bytes; | |
| 260 | +} | |
| 261 | + | |
| 262 | +/** | |
| 263 | + * struct_size() - Calculate size of structure with trailing array. | |
| 264 | + * @p: Pointer to the structure. | |
| 265 | + * @member: Name of the array member. | |
| 266 | + * @n: Number of elements in the array. | |
| 267 | + * | |
| 268 | + * Calculates size of memory needed for structure @p followed by an | |
| 269 | + * array of @n @member elements. | |
| 270 | + * | |
| 271 | + * Return: number of bytes needed or SIZE_MAX on overflow. | |
| 272 | + */ | |
| 273 | +#define struct_size(p, member, n) \ | |
| 274 | + __ab_c_size(n, \ | |
| 275 | + sizeof(*(p)->member) + __must_be_array((p)->member),\ | |
| 276 | + sizeof(*(p))) | |
| 277 | + | |
| 278 | +#endif /* __LINUX_OVERFLOW_H */ | |