From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dan Carpenter <dan.carpenter@oracle.com>
Date: Mon, 23 Feb 2015 15:44:19 +0000
Subject: [patch] groups: integer underflow in groups_alloc()
Message-Id: <20150223154419.GA2542@mwanda>
List-Id: <kernel-janitors.vger.kernel.org>
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To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Andy Lutomirski <luto@amacapital.net>, Wang YanQing <udknight@gmail.com>, linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org, kernel-janitors@vger.kernel.org

This is called from rsc_parse() with a use controlled value.  Say for
example that "gidsetsize" is negative, then we could end up allocating
less than sizeof(struct group_info) leading to memory corruption.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
I copied the NGROUPS_MAX limit from the surrounding code, I'm not
absolutely that it's the correct limit to use.

diff --git a/kernel/groups.c b/kernel/groups.c
index 664411f..e9341b3 100644
--- a/kernel/groups.c
+++ b/kernel/groups.c
@@ -18,6 +18,9 @@ struct group_info *groups_alloc(int gidsetsize)
 	int nblocks;
 	int i;
 
+	if ((unsigned)gidsetsize > NGROUPS_MAX)
+		return NULL;
+
 	nblocks = (gidsetsize + NGROUPS_PER_BLOCK - 1) / NGROUPS_PER_BLOCK;
 	/* Make sure we always allocate at least one indirect block pointer */
 	nblocks = nblocks ? : 1;