io_uring: io_wq_create() returns an error pointer, not NULL

syzbot reported an issue where we crash at setup time if failslab is
used. The issue is that io_wq_create() returns an error pointer on
failure, not NULL. Hence io_uring thought the io-wq was setup just
fine, but in reality it's a garbage error pointer.

Use IS_ERR() instead of a NULL check, and assign ret appropriately.

Reported-by: syzbot+221cc24572a2fed23b6b@syzkaller.appspotmail.com
Fixes: 561fb04a6a22 ("io_uring: replace workqueue usage with io-wq")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 8e25c25..72d2605 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3489,8 +3489,9 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
        /* Do QD, or 4 * CPUS, whatever is smallest */
        concurrency = min(ctx->sq_entries, 4 * num_online_cpus());
        ctx->io_wq = io_wq_create(concurrency, ctx->sqo_mm);
-       if (!ctx->io_wq) {
-               ret = -ENOMEM;
+       if (IS_ERR(ctx->io_wq)) {
+               ret = PTR_ERR(ctx->io_wq);
+               ctx->io_wq = NULL;
                goto err;
        }