linux-kernel - [PATCH 4.9 18/60] mm/slub.c: fix random

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Date:   Mon, 13 Feb 2017 05:03:50 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Sean Rees <sean@...fax.org>,
        userwithuid@...il.com, Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Thomas Garnier <thgarnie@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.9 18/60] mm/slub.c: fix random_seq offset destruction

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

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

From: Sean Rees <sean@...fax.org>

commit a810007afe239d59c1115fcaa06eb5b480f876e9 upstream.

Commit 210e7a43fa90 ("mm: SLUB freelist randomization") broke USB hub
initialisation as described in

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

Bail out 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).

Fixes: 210e7a43fa90 ("mm: SLUB freelist randomization")
Link: http://lkml.kernel.org/r/20170207140707.20824-1-sean@erifax.org
Signed-off-by: Sean Rees <sean@...fax.org>
Reported-by: <userwithuid@...il.com>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Pekka Enberg <penberg@...nel.org>
Cc: David Rientjes <rientjes@...gle.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
Cc: Thomas Garnier <thgarnie@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/slub.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1419,6 +1419,10 @@ static int init_cache_random_seq(struct
 	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",