netdev - [patch] rds: fix an integer overflow test in rds_info

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Message-ID: <20150801123326.GA5075@mwanda>
Date:	Sat, 1 Aug 2015 15:33:26 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Chien Yen <chien.yen@...cle.com>, Andy Grover <agrover@...hat.com>
Cc:	"David S. Miller" <davem@...emloft.net>, rds-devel@....oracle.com,
	netdev@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [patch] rds: fix an integer overflow test in rds_info_getsockopt()

"len" is a signed integer.  We check that len is not negative, so it
goes from zero to INT_MAX.  PAGE_SIZE is unsigned long so the comparison
is type promoted to unsigned long.  ULONG_MAX - 4095 is a higher than
INT_MAX so the condition can never be true.

I don't know if this is harmful but it seems safe to limit "len" to
INT_MAX - 4095.

Fixes: a8c879a7ee98 ('RDS: Info and stats')
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>

diff --git a/net/rds/info.c b/net/rds/info.c
index 9a6b4f6..140a44a 100644
--- a/net/rds/info.c
+++ b/net/rds/info.c
@@ -176,7 +176,7 @@ int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
 
 	/* check for all kinds of wrapping and the like */
 	start = (unsigned long)optval;
-	if (len < 0 || len + PAGE_SIZE - 1 < len || start + len < start) {
+	if (len < 0 || len > INT_MAX - PAGE_SIZE + 1 || start + len < start) {
 		ret = -EINVAL;
 		goto out;
 	}
--
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