linux-kernel - [PATCH] mm/slub: Fix random

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Message-Id: <20170207140707.20824-1-sean@erifax.org>
Date:   Tue,  7 Feb 2017 14:07:07 +0000
From:   Sean Rees <sean@...fax.org>
To:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        thgarnie@...gle.com, Sean Rees <sean@...fax.org>
Subject: [PATCH] mm/slub: Fix random_seq offset destruction

Bailout early from init_cache_random_seq if s->random_seq is already
initialised. This prevents destroying the previously computed random_seq
offsets later in the function.

If the offsets are destroyed, then shuffle_freelist will truncate
page->freelist to just the first object (orphaning the rest).

This fixes https://bugzilla.kernel.org/show_bug.cgi?id=177551.

Signed-off-by: Sean Rees <sean@...fax.org>
---
 mm/slub.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/slub.c b/mm/slub.c
index 7aa6f43..7ec0a96 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1422,6 +1422,10 @@ static int init_cache_random_seq(struct kmem_cache *s)
 	int err;
 	unsigned long i, count = oo_objects(s->oo);
 
+	/* Bailout if already initialised */
+	if (s->random_seq)
+		return 0;
+
 	err = cache_random_seq_create(s, count, GFP_KERNEL);
 	if (err) {
 		pr_err("SLUB: Unable to initialize free list for %s\n",
-- 
2.9.3