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

commit b71812168571fa55e44cdd0254471331b9c4c4c6 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index 3b3dcf719e0783e74ecf9018b3fd1728a31f6393..16eb99458df40667df3f180b98fc979eac38b4e7 100644 (file)
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -2053,7 +2053,9 @@ 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;
        }
 
@@ -2109,6 +2111,15 @@ 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;