netfilter: ebtables: CONFIG_COMPAT: don't trust userland offsets

We need to make sure the offsets are not out of range of the
total size.
Also check that they are in ascending order.

The WARN_ON triggered by syzkaller (it sets panic_on_warn) is
changed to also bail out, no point in continuing parsing.

Briefly tested with simple ruleset of
-A INPUT --limit 1/s' --log
plus jump to custom chains using 32bit ebtables binary.

Reported-by: <syzbot+845a53d13171abf8bf29@syzkaller.appspotmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index 61f8787..254ef9f 100644 (file)
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -2060,7 +2060,9 @@ static int ebt_size_mwt(struct compat_ebt_entry_mwt *match32,
                if (match_kern)
                        match_kern->match_size = ret;
 
-               WARN_ON(type == EBT_COMPAT_TARGET && size_left);
+               if (WARN_ON(type == EBT_COMPAT_TARGET && size_left))
+                       return -EINVAL;
+
                match32 = (struct compat_ebt_entry_mwt *) buf;
        }
 
@@ -2116,6 +2118,15 @@ static int size_entry_mwt(struct ebt_entry *entry, const unsigned char *base,
         *
         * offsets are relative to beginning of struct ebt_entry (i.e., 0).
         */
+       for (i = 0; i < 4 ; ++i) {
+               if (offsets[i] >= *total)
+                       return -EINVAL;
+               if (i == 0)
+                       continue;
+               if (offsets[i-1] > offsets[i])
+                       return -EINVAL;
+       }
+
        for (i = 0, j = 1 ; j < 4 ; j++, i++) {
                struct compat_ebt_entry_mwt *match32;
                unsigned int size;