diff options
| author | Junho Ryu <jayr@google.com> | 2013-12-03 18:10:28 -0500 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2014-02-15 19:20:12 +0000 |
| commit | ec94b7aba9ced72a96cfdf0cdf693b30ff604039 (patch) | |
| tree | ed231e17e0271c8d8a0b8535e74c915e5a5b6193 /fs | |
| parent | 9eb492b82ccf9900c85af95276b60dd1ba1b7d2a (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.c | 11 |
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; |