linux-kernel - [patch] groups: integer underflow in groups

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Message-ID: <20150223154419.GA2542@mwanda>
Date:	Mon, 23 Feb 2015 18:44:19 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Wang YanQing <udknight@...il.com>,
	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: [patch] groups: integer underflow in groups_alloc()

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@...cle.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;
--
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