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| author | Tejun Heo <tj@kernel.org> | 2019-10-06 17:58:09 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2019-10-07 15:47:19 -0700 |
| commit | 8e00c4e9dd852f7a9bf12234fad65a2f2f93788f (patch) | |
| tree | d6421d6735a16983dc9a12d44827832b2ddbe391 /fs/fs-writeback.c | |
| parent | 6d0e9849417bfcbe997405371e0ed712b364ba0a (diff) | |
| download | lwn-8e00c4e9dd852f7a9bf12234fad65a2f2f93788f.tar.gz lwn-8e00c4e9dd852f7a9bf12234fad65a2f2f93788f.zip | |
writeback: fix use-after-free in finish_writeback_work()
finish_writeback_work() reads @done->waitq after decrementing
@done->cnt. However, once @done->cnt reaches zero, @done may be freed
(from stack) at any moment and @done->waitq can contain something
unrelated by the time finish_writeback_work() tries to read it. This
led to the following crash.
"BUG: kernel NULL pointer dereference, address: 0000000000000002"
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 0 P4D 0
Oops: 0002 [#1] SMP DEBUG_PAGEALLOC
CPU: 40 PID: 555153 Comm: kworker/u98:50 Kdump: loaded Not tainted
...
Workqueue: writeback wb_workfn (flush-btrfs-1)
RIP: 0010:_raw_spin_lock_irqsave+0x10/0x30
Code: 48 89 d8 5b c3 e8 50 db 6b ff eb f4 0f 1f 40 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 53 9c 5b fa 31 c0 ba 01 00 00 00 <f0> 0f b1 17 75 05 48 89 d8 5b c3 89 c6 e8 fe ca 6b ff eb f2 66 90
RSP: 0018:ffffc90049b27d98 EFLAGS: 00010046
RAX: 0000000000000000 RBX: 0000000000000246 RCX: 0000000000000000
RDX: 0000000000000001 RSI: 0000000000000003 RDI: 0000000000000002
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001
R10: ffff889fff407600 R11: ffff88ba9395d740 R12: 000000000000e300
R13: 0000000000000003 R14: 0000000000000000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff88bfdfa00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000002 CR3: 0000000002409005 CR4: 00000000001606e0
Call Trace:
__wake_up_common_lock+0x63/0xc0
wb_workfn+0xd2/0x3e0
process_one_work+0x1f5/0x3f0
worker_thread+0x2d/0x3d0
kthread+0x111/0x130
ret_from_fork+0x1f/0x30
Fix it by reading and caching @done->waitq before decrementing
@done->cnt.
Link: http://lkml.kernel.org/r/20190924010631.GH2233839@devbig004.ftw2.facebook.com
Fixes: 5b9cce4c7eb069 ("writeback: Generalize and expose wb_completion")
Signed-off-by: Tejun Heo <tj@kernel.org>
Debugged-by: Chris Mason <clm@fb.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Cc: <stable@vger.kernel.org> [5.2+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/fs-writeback.c')
| -rw-r--r-- | fs/fs-writeback.c | 9 |
1 files changed, 7 insertions, 2 deletions
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 8aaa7eec7b74..e88421d9a48d 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -164,8 +164,13 @@ static void finish_writeback_work(struct bdi_writeback *wb, if (work->auto_free) kfree(work); - if (done && atomic_dec_and_test(&done->cnt)) - wake_up_all(done->waitq); + if (done) { + wait_queue_head_t *waitq = done->waitq; + + /* @done can't be accessed after the following dec */ + if (atomic_dec_and_test(&done->cnt)) + wake_up_all(waitq); + } } static void wb_queue_work(struct bdi_writeback *wb, |