Re: [kees:kspp/memcpy/next-20210816/v2 34/63] include/linux/fortify-string.h:265:4: warning: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()?
From: Namjae Jeon
Date: Sat Aug 28 2021 - 06:42:06 EST
Hi,
2021-08-28 17:55 GMT+09:00, kernel test robot <lkp@xxxxxxxxx>:
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git
> kspp/memcpy/next-20210816/v2
> head: 0f0894ea4d0761cc43917960b4878fa3d1ed7a5f
> commit: 1db8308d772a6ac9744a973ea07cbc811c608c04 [34/63] fortify: Detect
> struct member overflows in memcpy() at compile-time
> config: x86_64-allyesconfig (attached as .config)
> compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
> reproduce (this is a W=1 build):
> #
> https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/commit/?id=1db8308d772a6ac9744a973ea07cbc811c608c04
> git remote add kees
> https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git
> git fetch --no-tags kees kspp/memcpy/next-20210816/v2
> git checkout 1db8308d772a6ac9744a973ea07cbc811c608c04
> # save the attached .config to linux build tree
> make W=1 ARCH=x86_64
>
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
Thanks for your report!
>
> All warnings (new ones prefixed by >>):
>
> In file included from include/linux/string.h:253,
> from include/linux/bitmap.h:10,
> from include/linux/cpumask.h:12,
> from arch/x86/include/asm/cpumask.h:5,
> from arch/x86/include/asm/msr.h:11,
> from arch/x86/include/asm/processor.h:22,
> from arch/x86/include/asm/cpufeature.h:5,
> from arch/x86/include/asm/thread_info.h:53,
> from include/linux/thread_info.h:60,
> from arch/x86/include/asm/preempt.h:7,
> from include/linux/preempt.h:78,
> from include/linux/spinlock.h:51,
> from include/linux/wait.h:9,
> from include/linux/wait_bit.h:8,
> from include/linux/fs.h:6,
> from fs/ksmbd/ndr.c:7:
> In function 'fortify_memcpy_chk',
> inlined from 'ndr_read_string' at fs/ksmbd/ndr.c:86:2,
> inlined from 'ndr_decode_dos_attr' at fs/ksmbd/ndr.c:167:2:
>>> include/linux/fortify-string.h:265:4: warning: call to
>>> '__write_overflow_field' declared with attribute warning: detected write
>>> beyond size of field (1st parameter); maybe use struct_group()?
>>> [-Wattribute-warning]
> 265 | __write_overflow_field(p_size_field, size);
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We have fixed this issue reported by Dan Carpenter yesterday and
queued the patch to #cifsd-for-next.
Thanks!
>
>
> vim +/__write_overflow_field +265 include/linux/fortify-string.h
>
> 211
> 212 /*
> 213 * To make sure the compiler can enforce protection against buffer
> overflows,
> 214 * memcpy(), memmove(), and memset() must not be used beyond
> individual
> 215 * struct members. If you need to copy across multiple members,
> please use
> 216 * struct_group() to create a named mirror of an anonymous struct
> union.
> 217 * (e.g. see struct sk_buff.)
> 218 *
> 219 * Mitigation coverage
> 220 * Bounds checking at:
> 221 * +-------+-------+-------+-------+
> 222 * | Compile time | Run time |
> 223 * memcpy() argument sizes: | write | read | write | read |
> 224 * +-------+-------+-------+-------+
> 225 * memcpy(known, known, constant) | y | y | n/a | n/a
> |
> 226 * memcpy(unknown, known, constant) | n | y | V | n/a
> |
> 227 * memcpy(known, unknown, constant) | y | n | n/a | V
> |
> 228 * memcpy(unknown, unknown, constant) | n | n | V | V
> |
> 229 * memcpy(known, known, dynamic) | n | n | b | B
> |
> 230 * memcpy(unknown, known, dynamic) | n | n | V | B
> |
> 231 * memcpy(known, unknown, dynamic) | n | n | b | V
> |
> 232 * memcpy(unknown, unknown, dynamic) | n | n | V | V
> |
> 233 * +-------+-------+-------+-------+
> 234 *
> 235 * y = deterministic compile-time bounds checking
> 236 * n = cannot do deterministic compile-time bounds checking
> 237 * n/a = no run-time bounds checking needed since compile-time
> deterministic
> 238 * b = perform run-time bounds checking
> 239 * B = can perform run-time bounds checking, but current unenforced
> 240 * V = vulnerable to run-time overflow
> 241 *
> 242 */
> 243 __FORTIFY_INLINE void fortify_memcpy_chk(__kernel_size_t size,
> 244 const size_t p_size,
> 245 const size_t q_size,
> 246 const size_t p_size_field,
> 247 const size_t q_size_field,
> 248 const char *func)
> 249 {
> 250 if (__builtin_constant_p(size)) {
> 251 /*
> 252 * Length argument is a constant expression, so we
> 253 * can perform compile-time bounds checking where
> 254 * buffer sizes are known.
> 255 */
> 256
> 257 /* Error when size is larger than enclosing struct. */
> 258 if (p_size > p_size_field && p_size < size)
> 259 __write_overflow();
> 260 if (q_size > q_size_field && q_size < size)
> 261 __read_overflow2();
> 262
> 263 /* Warn when write size argument larger than dest field. */
> 264 if (p_size_field < size)
> > 265 __write_overflow_field(p_size_field, size);
> 266 /*
> 267 * Warn for source field over-read when building with W=1
> 268 * or when an over-write happened, so both can be fixed at
> 269 * the same time.
> 270 */
> 271 if ((IS_ENABLED(KBUILD_EXTRA_WARN1) || p_size_field < size) &&
> 272 q_size_field < size)
> 273 __read_overflow2_field(q_size_field, size);
> 274 }
> 275 /*
> 276 * At this point, length argument may not be a constant expression,
> 277 * so run-time bounds checking can be done where buffer sizes are
> 278 * known. (This is not an "else" because the above checks may only
> 279 * be compile-time warnings, and we want to still warn for run-time
> 280 * overflows.)
> 281 */
> 282
> 283 /*
> 284 * Always stop accesses beyond the struct that contains the
> 285 * field, when the buffer's remaining size is known.
> 286 * (The -1 test is to optimize away checks where the buffer
> 287 * lengths are unknown.)
> 288 */
> 289 if ((p_size != (size_t)(-1) && p_size < size) ||
> 290 (q_size != (size_t)(-1) && q_size < size))
> 291 fortify_panic(func);
> 292 }
> 293
>
> ---
> 0-DAY CI Kernel Test Service, Intel Corporation
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>