netdev - [PATCH net] netfilter: x_tables: avoid out-of-bounds reads in xt_request_find

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Date:   Wed, 24 Jan 2018 14:49:48 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     netdev <netdev@...r.kernel.org>, netfilter-devel@...r.kernel.org,
        Florian Westphal <fw@...len.de>
Subject: [PATCH net] netfilter: x_tables: avoid out-of-bounds reads in
 xt_request_find_match()

From: Eric Dumazet <edumazet@...gle.com>

It looks like syzbot found its way into netfilter territory.

Issue here is that @name comes from user space and might
not be null terminated.

Out-of-bound reads happen, KASAN is not happy.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: syzbot <syzkaller@...glegroups.com>
---
No Fixes: tag, bug seems to be a day-0 one.

diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 55802e97f906d1987ed78b4296584deb38e5f876..8516dc459b539342f44d2b2b3e21b140677c7826 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -210,6 +210,9 @@ xt_request_find_match(uint8_t nfproto, const char *name, uint8_t revision)
 {
 	struct xt_match *match;
 
+	if (strnlen(name, XT_EXTENSION_MAXNAMELEN) == XT_EXTENSION_MAXNAMELEN)
+		return ERR_PTR(-EINVAL);
+
 	match = xt_find_match(nfproto, name, revision);
 	if (IS_ERR(match)) {
 		request_module("%st_%s", xt_prefix[nfproto], name);