[43/48] slub: fix a possible memleak in __slab_alloc()

[Greg KH]

3.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <eric.dumazet@xxxxxxxxx>

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@xxxxxxxxx>
Signed-off-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Acked-by: Christoph Lameter <cl@xxxxxxxxx>
Signed-off-by: Pekka Enberg <penberg@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 mm/slub.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2077,6 +2077,11 @@ static void *__slab_alloc(struct kmem_ca
 		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 {


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