ublk: fix null-ptr-deref in ublk_queue_cmd#917
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ublk_queue_cmd() dereferences ios[tag].cmd without NULL check. The cmd
pointer can be NULL when ublk_cancel_cmd() races with IO dispatch during
server teardown:
CPU0 (partition scan work) CPU1 (io_uring cancel callback)
ublk_queue_rq()
ublk_prep_req() -> OK
check canceling -> false
ublk_start_cancel()
quiesce, set canceling, unquiesce
ublk_cancel_cmd()
io->cmd = NULL
ublk_queue_cmd()
cmd = ios[tag].cmd -> NULL
ublk_get_uring_cmd_pdu(cmd) -> null-ptr-deref
The race window exists because ublk_cancel_cmd() can execute between the
canceling flag check and the cmd dereference in ublk_queue_cmd(). This
cannot be closed with simple synchronization since blk_mq_quiesce_queue
only waits for in-flight dispatches, not requests already past the
canceling check.
Fix by checking cmd for NULL before dereferencing. When NULL, abort the
request via __ublk_abort_rq() which handles both recovery (requeue) and
non-recovery (end with IOERR) cases.
Fixes: 71f28f3 ("ublk_drv: add io_uring based userspace block driver")
Reported-by: syzbot+415b9ec753cd2a196087@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=415b9ec753cd2a196087
Signed-off-by: Yun Zhou <yun.zhou@windriver.com>
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Pull request for series with
subject: ublk: fix null-ptr-deref in ublk_queue_cmd
version: 1
url: https://patchwork.kernel.org/project/linux-block/list/?series=1104193