io_uring: sanitize double poll handling

There's a bit of confusion on the matching pairs of poll vs double poll,
depending on if the request is a pure poll (IORING_OP_POLL_ADD) or
poll driven retry.

Add io_poll_get_double() that returns the double poll waitqueue, if any,
and io_poll_get_single() that returns the original poll waitqueue. With
that, remove the argument to io_poll_remove_double().

Finally ensure that wait->private is cleared once the double poll handler
has run, so that remove knows it's already been seen.

Cc: stable@vger.kernel.org # v5.8
Reported-by: syzbot+7f617d4a9369028b8a2c@syzkaller.appspotmail.com
Fixes: 18bceab101ad ("io_uring: allow POLL_ADD with double poll_wait() users")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 7dd6df15bc498f8eb943d03d23288afdf77ad114..cb030912bf5e36a0e5a0e59916898ae1867081bb 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4649,9 +4649,24 @@ static bool io_poll_rewait(struct io_kiocb *req, struct io_poll_iocb *poll)
        return false;
 }
 
-static void io_poll_remove_double(struct io_kiocb *req, void *data)
+static struct io_poll_iocb *io_poll_get_double(struct io_kiocb *req)
 {
-       struct io_poll_iocb *poll = data;
+       /* pure poll stashes this in ->io, poll driven retry elsewhere */
+       if (req->opcode == IORING_OP_POLL_ADD)
+               return (struct io_poll_iocb *) req->io;
+       return req->apoll->double_poll;
+}
+
+static struct io_poll_iocb *io_poll_get_single(struct io_kiocb *req)
+{
+       if (req->opcode == IORING_OP_POLL_ADD)
+               return &req->poll;
+       return &req->apoll->poll;
+}
+
+static void io_poll_remove_double(struct io_kiocb *req)
+{
+       struct io_poll_iocb *poll = io_poll_get_double(req);
 
        lockdep_assert_held(&req->ctx->completion_lock);
 
@@ -4671,7 +4686,7 @@ static void io_poll_complete(struct io_kiocb *req, __poll_t mask, int error)
 {
        struct io_ring_ctx *ctx = req->ctx;
 
-       io_poll_remove_double(req, req->io);
+       io_poll_remove_double(req);
        req->poll.done = true;
        io_cqring_fill_event(req, error ? error : mangle_poll(mask));
        io_commit_cqring(ctx);
@@ -4711,7 +4726,7 @@ static int io_poll_double_wake(struct wait_queue_entry *wait, unsigned mode,
                               int sync, void *key)
 {
        struct io_kiocb *req = wait->private;
-       struct io_poll_iocb *poll = req->apoll->double_poll;
+       struct io_poll_iocb *poll = io_poll_get_single(req);
        __poll_t mask = key_to_poll(key);
 
        /* for instances that support it check for an event match first: */
@@ -4725,6 +4740,8 @@ static int io_poll_double_wake(struct wait_queue_entry *wait, unsigned mode,
                done = list_empty(&poll->wait.entry);
                if (!done)
                        list_del_init(&poll->wait.entry);
+               /* make sure double remove sees this as being gone */
+               wait->private = NULL;
                spin_unlock(&poll->head->lock);
                if (!done)
                        __io_async_wake(req, poll, mask, io_poll_task_func);
@@ -4808,7 +4825,7 @@ static void io_async_task_func(struct callback_head *cb)
        if (hash_hashed(&req->hash_node))
                hash_del(&req->hash_node);
 
-       io_poll_remove_double(req, apoll->double_poll);
+       io_poll_remove_double(req);
        spin_unlock_irq(&ctx->completion_lock);
 
        if (!READ_ONCE(apoll->poll.canceled))
@@ -4919,7 +4936,7 @@ static bool io_arm_poll_handler(struct io_kiocb *req)
        ret = __io_arm_poll_handler(req, &apoll->poll, &ipt, mask,
                                        io_async_wake);
        if (ret || ipt.error) {
-               io_poll_remove_double(req, apoll->double_poll);
+               io_poll_remove_double(req);
                spin_unlock_irq(&ctx->completion_lock);
                kfree(apoll->double_poll);
                kfree(apoll);
@@ -4951,14 +4968,13 @@ static bool io_poll_remove_one(struct io_kiocb *req)
 {
        bool do_complete;
 
+       io_poll_remove_double(req);
+
        if (req->opcode == IORING_OP_POLL_ADD) {
-               io_poll_remove_double(req, req->io);
                do_complete = __io_poll_remove_one(req, &req->poll);
        } else {
                struct async_poll *apoll = req->apoll;
 
-               io_poll_remove_double(req, apoll->double_poll);
-
                /* non-poll requests have submit ref still */
                do_complete = __io_poll_remove_one(req, &apoll->poll);
                if (do_complete) {