linux-kernel - [PATCH 3.2 004/153] netfilter: ebtables: CONFIG

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Message-ID: <lsq.1527677561.357755018@decadent.org.uk>
Date:   Wed, 30 May 2018 11:52:41 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "" <syzbot+845a53d13171abf8bf29@...kaller.appspotmail.com>,
        "Pablo Neira Ayuso" <pablo@...filter.org>,
        "Florian Westphal" <fw@...len.de>
Subject: [PATCH 3.2 004/153] netfilter: ebtables: CONFIG_COMPAT: don't
 trust userland offsets

3.2.102-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Florian Westphal <fw@...len.de>

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@...kaller.appspotmail.com>
Signed-off-by: Florian Westphal <fw@...len.de>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/bridge/netfilter/ebtables.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -2004,7 +2004,9 @@ static int ebt_size_mwt(struct compat_eb
 		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;
 	}
 
@@ -2061,6 +2063,15 @@ static int size_entry_mwt(struct ebt_ent
 	 *
 	 * 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;