4.17-stable review patch. If anyone has any objections, please let me know.
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From: Florian Westphal fw@strlen.de
commit 11ff7288beb2b7da889a014aff0a7b80bf8efcf3 upstream.
the ebtables evaluation loop expects targets to return positive values (jumps), or negative values (absolute verdicts).
This is completely different from what xtables does. In xtables, targets are expected to return the standard netfilter verdicts, i.e. NF_DROP, NF_ACCEPT, etc.
ebtables will consider these as jumps.
Therefore reject any target found due to unspec fallback. v2: also reject watchers. ebtables ignores their return value, so a target that assumes skb ownership (and returns NF_STOLEN) causes use-after-free.
The only watchers in the 'ebtables' front-end are log and nflog; both have AF_BRIDGE specific wrappers on kernel side.
Reported-by: syzbot+2b43f681169a2a0d306a@syzkaller.appspotmail.com Signed-off-by: Florian Westphal fw@strlen.de Signed-off-by: Pablo Neira Ayuso pablo@netfilter.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- net/bridge/netfilter/ebtables.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
--- a/net/bridge/netfilter/ebtables.c +++ b/net/bridge/netfilter/ebtables.c @@ -396,6 +396,12 @@ ebt_check_watcher(struct ebt_entry_watch watcher = xt_request_find_target(NFPROTO_BRIDGE, w->u.name, 0); if (IS_ERR(watcher)) return PTR_ERR(watcher); + + if (watcher->family != NFPROTO_BRIDGE) { + module_put(watcher->me); + return -ENOENT; + } + w->u.watcher = watcher;
par->target = watcher; @@ -717,6 +723,13 @@ ebt_check_entry(struct ebt_entry *e, str goto cleanup_watchers; }
+ /* Reject UNSPEC, xtables verdicts/return values are incompatible */ + if (target->family != NFPROTO_BRIDGE) { + module_put(target->me); + ret = -ENOENT; + goto cleanup_watchers; + } + t->u.target = target; if (t->u.target == &ebt_standard_target) { if (gap < sizeof(struct ebt_standard_target)) {