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authorJunho Ryu <jayr@google.com>2013-12-03 18:10:28 -0500
committerBen Hutchings <ben@decadent.org.uk>2014-02-15 19:20:12 +0000
commitec94b7aba9ced72a96cfdf0cdf693b30ff604039 (patch)
treeed231e17e0271c8d8a0b8535e74c915e5a5b6193 /fs
parent9eb492b82ccf9900c85af95276b60dd1ba1b7d2a (diff)
ext4: fix use-after-free in ext4_mb_new_blocks
commit 4e8d2139802ce4f41936a687f06c560b12115247 upstream. ext4_mb_put_pa should hold pa->pa_lock before accessing pa->pa_count. While ext4_mb_use_preallocated checks pa->pa_deleted first and then increments pa->count later, ext4_mb_put_pa decrements pa->pa_count before holding pa->pa_lock and then sets pa->pa_deleted. * Free sequence ext4_mb_put_pa (1): atomic_dec_and_test pa->pa_count ext4_mb_put_pa (2): lock pa->pa_lock ext4_mb_put_pa (3): check pa->pa_deleted ext4_mb_put_pa (4): set pa->pa_deleted=1 ext4_mb_put_pa (5): unlock pa->pa_lock ext4_mb_put_pa (6): remove pa from a list ext4_mb_pa_callback: free pa * Use sequence ext4_mb_use_preallocated (1): iterate over preallocation ext4_mb_use_preallocated (2): lock pa->pa_lock ext4_mb_use_preallocated (3): check pa->pa_deleted ext4_mb_use_preallocated (4): increase pa->pa_count ext4_mb_use_preallocated (5): unlock pa->pa_lock ext4_mb_release_context: access pa * Use-after-free sequence [initial status] <pa->pa_deleted = 0, pa_count = 1> ext4_mb_use_preallocated (1): iterate over preallocation ext4_mb_use_preallocated (2): lock pa->pa_lock ext4_mb_use_preallocated (3): check pa->pa_deleted ext4_mb_put_pa (1): atomic_dec_and_test pa->pa_count [pa_count decremented] <pa->pa_deleted = 0, pa_count = 0> ext4_mb_use_preallocated (4): increase pa->pa_count [pa_count incremented] <pa->pa_deleted = 0, pa_count = 1> ext4_mb_use_preallocated (5): unlock pa->pa_lock ext4_mb_put_pa (2): lock pa->pa_lock ext4_mb_put_pa (3): check pa->pa_deleted ext4_mb_put_pa (4): set pa->pa_deleted=1 [race condition!] <pa->pa_deleted = 1, pa_count = 1> ext4_mb_put_pa (5): unlock pa->pa_lock ext4_mb_put_pa (6): remove pa from a list ext4_mb_pa_callback: free pa ext4_mb_release_context: access pa AddressSanitizer has detected use-after-free in ext4_mb_new_blocks Bug report: http://goo.gl/rG1On3 Signed-off-by: Junho Ryu <jayr@google.com> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'fs')
-rw-r--r--fs/ext4/mballoc.c11
1 files changed, 8 insertions, 3 deletions
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 9b8c131ffa5a..e5dc9a6a9b22 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3378,6 +3378,9 @@ static void ext4_mb_pa_callback(struct rcu_head *head)
{
struct ext4_prealloc_space *pa;
pa = container_of(head, struct ext4_prealloc_space, u.pa_rcu);
+
+ BUG_ON(atomic_read(&pa->pa_count));
+ BUG_ON(pa->pa_deleted == 0);
kmem_cache_free(ext4_pspace_cachep, pa);
}
@@ -3391,11 +3394,13 @@ static void ext4_mb_put_pa(struct ext4_allocation_context *ac,
ext4_group_t grp;
ext4_fsblk_t grp_blk;
- if (!atomic_dec_and_test(&pa->pa_count) || pa->pa_free != 0)
- return;
-
/* in this short window concurrent discard can set pa_deleted */
spin_lock(&pa->pa_lock);
+ if (!atomic_dec_and_test(&pa->pa_count) || pa->pa_free != 0) {
+ spin_unlock(&pa->pa_lock);
+ return;
+ }
+
if (pa->pa_deleted == 1) {
spin_unlock(&pa->pa_lock);
return;