[PATCH 5.16 009/164] io_uring: disallow modification of rsrc_data during quiesce

Greg Kroah-Hartman
2022-02-28T18:00:45Z

From: Dylan Yudaken <dylany@fb.com>

commit 80912cef18f16f8fe59d1fb9548d4364342be360 upstream.

io_rsrc_ref_quiesce will unlock the uring while it waits for references to
the io_rsrc_data to be killed.
There are other places to the data that might add references to data via
calls to io_rsrc_node_switch.
There is a race condition where this reference can be added after the
completion has been signalled. At this point the io_rsrc_ref_quiesce call
will wake up and relock the uring, assuming the data is unused and can be
freed - although it is actually being used.

To fix this check in io_rsrc_ref_quiesce if a resource has been revived.

Reported-by: syzbot+ca8bf833622a1662745b@syzkaller.appspotmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220222161751.995746-1-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/io_uring.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -7865,7 +7865,15 @@ static __cold int io_rsrc_ref_quiesce(st
ret = wait_for_completion_interruptible(&data->done);
if (!ret) {
mutex_lock(&ctx->uring_lock);
- break;
+ if (atomic_read(&data->refs) > 0) {
+ /*
+ * it has been revived by another thread while
+ * we were unlocked
+ */
+ mutex_unlock(&ctx->uring_lock);
+ } else {
+ break;
+ }
}

atomic_inc(&data->refs);