linux-kernel - [PATCH] kernel/groups.c: Minor bugfix for overflow in binary search

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Message-Id: <1FB729E1-8CAA-4EEF-ABA4-200471843503@andrew.cmu.edu>
Date:	Fri, 30 Sep 2011 00:39:17 -0400
From:	Josh Zimmerman <jzimmerm@...rew.cmu.edu>
To:	akpm@...ux-foundation.org, serge.hallyn@...onical.com,
	ebiederm@...ssion.com, dhowells@...hat.com, daniel.lezcano@...e.fr
Cc:	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: [PATCH] kernel/groups.c: Minor bugfix for overflow in binary search

From: Josh Zimmerman

Fixed possible unsigned int overflow bug. (2 + 2^(32) - 1)/2 results in overflow; 2 + (2^(32)-1-2)/2 does not.

Signed-off-by: Josh Zimmerman <joshz@....edu>

---

--- kernel/groups.c.orig	2011-09-29 23:58:45.000000000 -0400
+++ kernel/groups.c	2011-09-29 23:59:13.000000000 -0400
@@ -142,7 +142,7 @@ int groups_search(const struct group_inf
 	left = 0;
 	right = group_info->ngroups;
 	while (left < right) {
-		unsigned int mid = (left+right)/2;
+		unsigned int mid = left +  (right - left)/2;
 		if (grp > GROUP_AT(group_info, mid))
 			left = mid + 1;
 		else if (grp < GROUP_AT(group_info, mid))


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