From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Tue, 13 Dec 2011 03:57:06 +0000 (+0100)
Subject: slub: fix a possible memleak in __slab_alloc()
X-Git-Tag: v3.2.2~88
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=65722fdd70758e2f1ac30f42f54c056631062fd5;p=thirdparty%2Fkernel%2Fstable.git

slub: fix a possible memleak in __slab_alloc()

commit 73736e0387ba0e6d2b703407b4d26168d31516a7 upstream.

Zhihua Che reported a possible memleak in slub allocator on
CONFIG_PREEMPT=y builds.

It is possible current thread migrates right before disabling irqs in
__slab_alloc(). We must check again c->freelist, and perform a normal
allocation instead of scratching c->freelist.

Many thanks to Zhihua Che for spotting this bug, introduced in 2.6.39

V2: Its also possible an IRQ freed one (or several) object(s) and
populated c->freelist, so its not a CONFIG_PREEMPT only problem.

Reported-by: Zhihua Che <zhihua.che@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---

diff --git a/mm/slub.c b/mm/slub.c
index ed3334d9b6da7..1a919f0150f51 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2166,6 +2166,11 @@ redo:
 		goto new_slab;
 	}
 
+	/* must check again c->freelist in case of cpu migration or IRQ */
+	object = c->freelist;
+	if (object)
+		goto load_freelist;
+
 	stat(s, ALLOC_SLOWPATH);
 
 	do {