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authorThomas Gleixner <tglx@linutronix.de>2017-06-02 14:46:25 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-06-07 12:07:49 +0200
commitc1bb2a899b5f5edc10cd5b5b9b0496cddb533565 (patch)
tree7b4c40d67d33740892c2afc03de4ab61fb6fd1a0
parent873f3b0ebbfe454f092d038a4bd1e0e17622c786 (diff)
downloadlinux-aarch64-c1bb2a899b5f5edc10cd5b5b9b0496cddb533565.tar.gz
slub/memcg: cure the brainless abuse of sysfs attributes
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>
-rw-r--r--mm/slub.c6
1 files changed, 4 insertions, 2 deletions
diff --git a/mm/slub.c b/mm/slub.c
index 58c7526f8de2..912aedda1633 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5452,6 +5452,7 @@ static void memcg_propagate_slab_attrs(struct kmem_cache *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;
@@ -5476,8 +5477,9 @@ static void memcg_propagate_slab_attrs(struct kmem_cache *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)