linux-kernel - [PATCH] netfilter: fix int overflow in xt_alloc_table

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Message-Id: <20171228084854.247843-1-dvyukov@google.com>
Date:   Thu, 28 Dec 2017 09:48:54 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     pablo@...filter.org, kadlec@...ckhole.kfki.hu, fw@...len.de,
        davem@...emloft.net
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] netfilter: fix int overflow in xt_alloc_table_info()

syzkaller triggered OOM kills by passing ipt_replace.size = -1
to IPT_SO_SET_REPLACE. The root cause is that SMP_ALIGN() in
xt_alloc_table_info() causes int overflow and the size check passes
when it should not. SMP_ALIGN() is no longer needed leftover.

Remove SMP_ALIGN() call in xt_alloc_table_info().

Reported-by: syzbot+4396883fa8c4f64e0175@...kaller.appspotmail.com
Signed-off-by: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Pablo Neira Ayuso <pablo@...filter.org>
Cc: Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>
Cc: Florian Westphal <fw@...len.de>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: netfilter-devel@...r.kernel.org
Cc: coreteam@...filter.org
Cc: netdev@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
---
 net/netfilter/x_tables.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 55802e97f906..e02a21549c99 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -39,7 +39,6 @@ MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Harald Welte <laforge@...filter.org>");
 MODULE_DESCRIPTION("{ip,ip6,arp,eb}_tables backend module");
 
-#define SMP_ALIGN(x) (((x) + SMP_CACHE_BYTES-1) & ~(SMP_CACHE_BYTES-1))
 #define XT_PCPU_BLOCK_SIZE 4096
 
 struct compat_delta {
@@ -1000,7 +999,7 @@ struct xt_table_info *xt_alloc_table_info(unsigned int size)
 		return NULL;
 
 	/* Pedantry: prevent them from hitting BUG() in vmalloc.c --RR */
-	if ((SMP_ALIGN(size) >> PAGE_SHIFT) + 2 > totalram_pages)
+	if ((size >> PAGE_SHIFT) + 2 > totalram_pages)
 		return NULL;
 
 	info = kvmalloc(sz, GFP_KERNEL);
-- 
2.15.1.620.gb9897f4670-goog