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netfilter: ebtables: fix fortify warnings in size_entry_mwt()

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When compiling with gcc 13 and CONFIG_FORTIFY_SOURCE=y, the following
warning appears:

In function ‘fortify_memcpy_chk’,
    inlined from ‘size_entry_mwt’ at net/bridge/netfilter/ebtables.c:2118:2:
./include/linux/fortify-string.h:592:25: error: call to ‘__read_overflow2_field’
declared with attribute warning: detected read beyond size of field (2nd parameter);
maybe use struct_group()? [-Werror=attribute-warning]
  592 |                         __read_overflow2_field(q_size_field, size);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The compiler is complaining:

memcpy(&offsets[1], &entry->watchers_offset,
                       sizeof(offsets) - sizeof(offsets[0]));

where memcpy reads beyong &entry->watchers_offset to copy
{watchers,target,next}_offset altogether into offsets[]. Silence the
warning by wrapping these three up via struct_group().

Signed-off-by: GONG, Ruiqi <gongruiqi1@huawei.com>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Florian Westphal <fw@strlen.de>
This commit is contained in:
GONG, Ruiqi 2023-08-09 15:45:03 +08:00 committed by Florian Westphal
parent 43c2817225
commit a7ed3465da
2 changed files with 9 additions and 8 deletions
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14
include/uapi/linux/netfilter_bridge/ebtables.h
View file

@ -182,12 +182,14 @@ struct ebt_entry {
unsigned char sourcemsk[ETH_ALEN];
unsigned char destmac[ETH_ALEN];
unsigned char destmsk[ETH_ALEN];
/* sizeof ebt_entry + matches */
unsigned int watchers_offset;
/* sizeof ebt_entry + matches + watchers */
unsigned int target_offset;
/* sizeof ebt_entry + matches + watchers + target */
unsigned int next_offset;
__struct_group(/* no tag */, offsets, /* no attrs */,
/* sizeof ebt_entry + matches */
unsigned int watchers_offset;
/* sizeof ebt_entry + matches + watchers */
unsigned int target_offset;
/* sizeof ebt_entry + matches + watchers + target */
unsigned int next_offset;
);
unsigned char elems[0] __attribute__ ((aligned (__alignof__(struct ebt_replace))));
};

3
net/bridge/netfilter/ebtables.c
View file

@ -2115,8 +2115,7 @@ static int size_entry_mwt(const struct ebt_entry *entry, const unsigned char *ba
return ret;
offsets[0] = sizeof(struct ebt_entry); /* matches come first */
memcpy(&offsets[1], &entry->watchers_offset,
sizeof(offsets) - sizeof(offsets[0]));
memcpy(&offsets[1], &entry->offsets, sizeof(entry->offsets));
if (state->buf_kern_start) {
buf_start = state->buf_kern_start + state->buf_kern_offset;