On August 8, 2023 9:32:50 AM PDT, "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx> wrote:
>On Tue, Aug 08, 2023 at 09:30:38PM +0800, GONG, Ruiqi wrote:
>> From: "GONG, Ruiqi" <gongruiqi1@xxxxxxxxxx>
>>
>> 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@xxxxxxxxxx>
>> ---
>>
>> v2: fix HDRTEST error by replacing struct_group() with __struct_group(),
>> since it's a uapi header.
>>
>> include/uapi/linux/netfilter_bridge/ebtables.h | 14 ++++++++------
>> net/bridge/netfilter/ebtables.c | 3 +--
>> 2 files changed, 9 insertions(+), 8 deletions(-)
>>
>> diff --git a/include/uapi/linux/netfilter_bridge/ebtables.h b/include/uapi/linux/netfilter_bridge/ebtables.h
>> index a494cf43a755..b0caad82b693 100644
>> --- a/include/uapi/linux/netfilter_bridge/ebtables.h
>> +++ b/include/uapi/linux/netfilter_bridge/ebtables.h
>> @@ -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))));
>> };
Actually, looking at what size_entry_mwt() is doing, I think you probably DO want a tag for this and to use a real structure for the manipulations instead of doing array indexing? I dunno. This is a weird function! :)
-Kees
>>
>> diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
>> index 757ec46fc45a..5ec66b1ebb64 100644
>> --- a/net/bridge/netfilter/ebtables.c
>> +++ b/net/bridge/netfilter/ebtables.c
>> @@ -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(offsets) - sizeof(offsets[0]));
> ^^^^^^^^^^^^
>You now can replace this ____________________________________|
>with just `sizeof(entry->offsets)`
>
>With that change you can add my
>Reviewed-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
>
>Thank you
>--
>Gustavo
>
>>
>> if (state->buf_kern_start) {
>> buf_start = state->buf_kern_start + state->buf_kern_offset;
>> --
>> 2.41.0
>>
--
Kees Cook
