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Florian Westphal authored
syzbot reported following splat: BUG: KASAN: vmalloc-out-of-bounds in size_entry_mwt net/bridge/netfilter/ebtables.c:2063 [inline] BUG: KASAN: vmalloc-out-of-bounds in compat_copy_entries+0x128b/0x1380 net/bridge/netfilter/ebtables.c:2155 Read of size 4 at addr ffffc900004461f4 by task syz-executor267/7937 CPU: 1 PID: 7937 Comm: syz-executor267 Not tainted 5.5.0-rc1-syzkaller #0 size_entry_mwt net/bridge/netfilter/ebtables.c:2063 [inline] compat_copy_entries+0x128b/0x1380 net/bridge/netfilter/ebtables.c:2155 compat_do_replace+0x344/0x720 net/bridge/netfilter/ebtables.c:2249 compat_do_ebt_set_ctl+0x22f/0x27e net/bridge/netfilter/ebtables.c:2333 [..] Because padding isn't considered during computation of ->buf_user_offset, "total" is decremented by fewer bytes than it should. Therefore, the first part of if (*total < sizeof(*entry) || entry->next_offset < sizeof(*entry)) will pass, -- it should not have. This causes oob access: entry->next_offset is past the vmalloced size. Reject padding and check that computed user offset (sum of ebt_entry structure plus all individual matches/watchers/targets) is same value that userspace gave us as the offset of the next entry. Reported-by: syzbot+f68108fed972453a0ad4@syzkaller.appspotmail.com Fixes: 81e675c2 ("netfilter: ebtables: add CONFIG_COMPAT support") Signed-off-by:
Florian Westphal <fw@strlen.de> Signed-off-by:
Pablo Neira Ayuso <pablo@netfilter.org>
e608f631