[Bridge] [PATCH AUTOSEL 4.14 6/8] netfilter: ebtables: fix fortify warnings in size_entry_mwt()

[Sasha Levin]

From: "GONG, Ruiqi" <gongrui...@huawei.com>

[ Upstream commit a7ed3465daa240bdf01a5420f64336fee879c09d ]

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 <gongrui...@huawei.com>
Reviewed-by: Gustavo A. R. Silva <gustavo...@kernel.org>
Reviewed-by: Kees Cook <keesc...@chromium.org>
Signed-off-by: Florian Westphal <f...@strlen.de>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
 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 9ff57c0a01990..43db01c05c4d5 100644
--- a/include/uapi/linux/netfilter_bridge/ebtables.h
+++ b/include/uapi/linux/netfilter_bridge/ebtables.h
@@ -172,12 +172,14 @@ 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))));
 };
 
diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index 84d4b4a0b0536..b5fb880c8a093 100644
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -2071,8 +2071,7 @@ 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;
-- 
2.40.1