[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: kernel test robot
Date: Sat Aug 28 2021 - 04:56:31 EST

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>

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);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


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

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