io_uring: fix race between timeout flush and removal

BugLink: https://bugs.launchpad.net/bugs/1969107
commit e677edbcabee849bfdd43f1602bccbecf736a646 upstream.

io_flush_timeouts() assumes the timeout isn't in progress of triggering
or being removed/canceled, so it unconditionally removes it from the
timeout list and attempts to cancel it.

Leave it on the list and let the normal timeout cancelation take care
of it.

Cc: stable@vger.kernel.org # 5.5+
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit ba7261af2b030ab2c06189be1fc77b273716839f)
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index a3a17596592949346ee5f7b51f621a403ed293f4..3d44d48b35ea8c78a645ed0b5f2b81bd419ab843 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1538,12 +1538,11 @@ static void io_flush_timeouts(struct io_ring_ctx *ctx)
        __must_hold(&ctx->completion_lock)
 {
        u32 seq = ctx->cached_cq_tail - atomic_read(&ctx->cq_timeouts);
+       struct io_kiocb *req, *tmp;
 
        spin_lock_irq(&ctx->timeout_lock);
-       while (!list_empty(&ctx->timeout_list)) {
+       list_for_each_entry_safe(req, tmp, &ctx->timeout_list, timeout.list) {
                u32 events_needed, events_got;
-               struct io_kiocb *req = list_first_entry(&ctx->timeout_list,
-                                               struct io_kiocb, timeout.list);
 
                if (io_is_timeout_noseq(req))
                        break;
@@ -1560,7 +1559,6 @@ static void io_flush_timeouts(struct io_ring_ctx *ctx)
                if (events_got < events_needed)
                        break;
 
-               list_del_init(&req->timeout.list);
                io_kill_timeout(req, 0);
        }
        ctx->cq_last_tm_flush = seq;
@@ -6205,6 +6203,7 @@ static int io_timeout_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe,
        if (get_timespec64(&data->ts, u64_to_user_ptr(sqe->addr)))
                return -EFAULT;
 
+       INIT_LIST_HEAD(&req->timeout.list);
        data->mode = io_translate_timeout_mode(flags);
        hrtimer_init(&data->timer, io_timeout_get_clock(data), data->mode);