From: Qian Cai cai@lca.pw
[ Upstream commit a68ee0573991e90af2f1785db309206408bad3e5 ]
There is no need to copy SLUB_STATS items from root memcg cache to new memcg cache copies. Doing so could result in stack overruns because the store function only accepts 0 to clear the stat and returns an error for everything else while the show method would print out the whole stat.
Then, the mismatch of the lengths returns from show and store methods happens in memcg_propagate_slab_attrs():
else if (root_cache->max_attr_size < ARRAY_SIZE(mbuf)) buf = mbuf;
max_attr_size is only 2 from slab_attr_store(), then, it uses mbuf[64] in show_stat() later where a bounch of sprintf() would overrun the stack variable. Fix it by always allocating a page of buffer to be used in show_stat() if SLUB_STATS=y which should only be used for debug purpose.
# echo 1 > /sys/kernel/slab/fs_cache/shrink BUG: KASAN: stack-out-of-bounds in number+0x421/0x6e0 Write of size 1 at addr ffffc900256cfde0 by task kworker/76:0/53251
Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019 Workqueue: memcg_kmem_cache memcg_kmem_cache_create_func Call Trace: number+0x421/0x6e0 vsnprintf+0x451/0x8e0 sprintf+0x9e/0xd0 show_stat+0x124/0x1d0 alloc_slowpath_show+0x13/0x20 __kmem_cache_create+0x47a/0x6b0
addr ffffc900256cfde0 is located in stack of task kworker/76:0/53251 at offset 0 in frame: process_one_work+0x0/0xb90
this frame has 1 object: [32, 72) 'lockdep_map'
Memory state around the buggy address: ffffc900256cfc80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffffc900256cfd00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffffc900256cfd80: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
^ ffffc900256cfe00: 00 00 00 00 00 f2 f2 f2 00 00 00 00 00 00 00 00 ffffc900256cfe80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ================================================================== Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: __kmem_cache_create+0x6ac/0x6b0 Workqueue: memcg_kmem_cache memcg_kmem_cache_create_func Call Trace: __kmem_cache_create+0x6ac/0x6b0
Fixes: 107dab5c92d5 ("slub: slub-specific propagation changes") Signed-off-by: Qian Cai cai@lca.pw Signed-off-by: Andrew Morton akpm@linux-foundation.org Cc: Glauber Costa glauber@scylladb.com Cc: Christoph Lameter cl@linux.com Cc: Pekka Enberg penberg@kernel.org Cc: David Rientjes rientjes@google.com Cc: Joonsoo Kim iamjoonsoo.kim@lge.com Link: http://lkml.kernel.org/r/20200429222356.4322-1-cai@lca.pw Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- mm/slub.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/mm/slub.c b/mm/slub.c index 63f372366ec59..660f4324c0972 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -5681,7 +5681,8 @@ static void memcg_propagate_slab_attrs(struct kmem_cache *s) */ if (buffer) buf = buffer; - else if (root_cache->max_attr_size < ARRAY_SIZE(mbuf)) + else if (root_cache->max_attr_size < ARRAY_SIZE(mbuf) && + !IS_ENABLED(CONFIG_SLUB_STATS)) buf = mbuf; else { buffer = (char *) get_zeroed_page(GFP_KERNEL);