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Date: Sat, 20 May 2017 12:52:03 +0200 (CEST) From: Thomas Gleixner <tglx@...utronix.de> To: LKML <linux-kernel@...r.kernel.org> cc: linux-mm@...ck.org, Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, Christoph Lameter <cl@...ux.com>, Andrew Morton <akpm@...ux-foundation.org>, Steven Rostedt <rostedt@...dmis.org>, Peter Zijlstra <peterz@...radead.org> Subject: [PATCH] slub/memcg: Cure the brainless abuse of sysfs attributes memcg_propagate_slab_attrs() abuses the sysfs attribute file functions to propagate settings from the root kmem_cache to a newly created kmem_cache. It does that with: attr->show(root, buf); attr->store(new, buf, strlen(bug); Aside of being a lazy and absurd hackery this is broken because it does not check the return value of the show() function. Some of the show() functions return 0 w/o touching the buffer. That means in such a case the store function is called with the stale content of the previous show(). That causes nonsense like invoking kmem_cache_shrink() on a newly created kmem_cache. In the worst case it would cause handing in an uninitialized buffer. This should be rewritten proper by adding a propagate() callback to those slub_attributes which must be propagated and avoid that insane conversion to and from ASCII, but that's too large for a hot fix. Check at least the return value of the show() function, so calling store() with stale content is prevented. Reported-by: Steven Rostedt <rostedt@...dmis.org> Signed-off-by: Thomas Gleixner <tglx@...utronix.de> Cc: stable@...r.kernel.org --- mm/slub.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- a/mm/slub.c +++ b/mm/slub.c @@ -5512,6 +5512,7 @@ static void memcg_propagate_slab_attrs(s char mbuf[64]; char *buf; struct slab_attribute *attr = to_slab_attr(slab_attrs[i]); + ssize_t len; if (!attr || !attr->store || !attr->show) continue; @@ -5536,8 +5537,9 @@ static void memcg_propagate_slab_attrs(s buf = buffer; } - attr->show(root_cache, buf); - attr->store(s, buf, strlen(buf)); + len = attr->show(root_cache, buf); + if (len > 0) + attr->store(s, buf, len); } if (buffer)
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