io_uring: io_allocate_scq_urings() should return a sane state

to #26323578

commit eb065d301e8c83643367bdb0898becc364046bda upstream.

We currently rely on the ring destroy on cleaning things up in case of
failure, but io_allocate_scq_urings() can leave things half initialized
if only parts of it fails.

Be nice and return with either everything setup in success, or return an
error with things nicely cleaned up.

Reported-by: syzbot+0d818c0d39399188f393@syzkaller.appspotmail.com
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJoseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: NXiaoguang Wang <xiaoguang.wang@linux.alibaba.com>

fs/io_uring.c

@@ -4593,12 +4593,18 @@ static int io_allocate_scq_urings(struct io_ring_ctx *ctx,
 	ctx->cq_entries = rings->cq_ring_entries;
 
 	size = array_size(sizeof(struct io_uring_sqe), p->sq_entries);
-	if (size == SIZE_MAX)
+	if (size == SIZE_MAX) {
+		io_mem_free(ctx->rings);
+		ctx->rings = NULL;
 		return -EOVERFLOW;
+	}
 
 	ctx->sq_sqes = io_mem_alloc(size);
-	if (!ctx->sq_sqes)
+	if (!ctx->sq_sqes) {
+		io_mem_free(ctx->rings);
+		ctx->rings = NULL;
 		return -ENOMEM;
+	}
 
 	return 0;
 }