ext4: fix use-after-free in ext4_mb_new_blocks
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>
Cc: stable@vger.kernel.org
1 file changed