Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 3.18 21/33] slub/memcg: cure the brainless abuse of sysfs attributes | Date | Mon, 5 Jun 2017 18:17:14 +0200 |
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3.18-stable review patch. If anyone has any objections, please let me know.
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From: Thomas Gleixner <tglx@linutronix.de>
commit 478fe3037b2278d276d4cd9cd0ab06c4cb2e9b32 upstream.
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.
Steven said: "It can cause a deadlock with get_online_cpus() that has been uncovered by recent cpu hotplug and lockdep changes that Thomas and Peter have been doing.
Possible unsafe locking scenario:
CPU0 CPU1 ---- ---- lock(cpu_hotplug.lock); lock(slab_mutex); lock(cpu_hotplug.lock); lock(slab_mutex);
*** DEADLOCK ***"
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1705201244540.2255@nanos Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reported-by: Steven Rostedt <rostedt@goodmis.org> Acked-by: David Rientjes <rientjes@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Christoph Lameter <cl@linux.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Christoph Hellwig <hch@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- mm/slub.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
--- a/mm/slub.c +++ b/mm/slub.c @@ -4959,6 +4959,7 @@ 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; @@ -4983,8 +4984,9 @@ 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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