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 <rost...@goodmis.org>
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Cc: sta...@vger.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)
