netfilter: ebtables: reject non-bridge targets

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>

diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index 25738b20676d50d98f573f0c609738d4ee62c103..54c7fe68040f7e060cdd0b1bd56f54da23f630b1 100644 (file)
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -398,6 +398,12 @@ 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;
@@ -719,6 +725,13 @@ 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)) {