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 taret 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@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
---
net/bridge/netfilter/ebtables.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index 6ba639f6c51d..62a303b68952 100644
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -396,6 +396,12 @@ ebt_check_watcher(struct ebt_entry_watcher *w, struct xt_tgchk_param *par,
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;
@@ -715,6 +721,13 @@ ebt_check_entry(struct ebt_entry *e, struct net *net,
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)) {
--
2.16.4
--
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