io_uring: convert io_buffer_idr to XArray

Like we did for the personality idr, convert the IO buffer idr to use
XArray. This avoids a use-after-free on removal of entries, since idr
doesn't like doing so from inside an iterator, and it nicely reduces
the amount of code we need to support this feature.

Fixes: 5a2e745d ("io_uring: buffer registration infrastructure")
Cc: stable@vger.kernel.org
Cc: Matthew Wilcox <willy@infradead.org>
Cc: yangerkun <yangerkun@huawei.com>
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -402,7 +402,7 @@ struct io_ring_ctx {
 	struct socket		*ring_sock;
 #endif
 
-	struct idr		io_buffer_idr;
+	struct xarray		io_buffers;
 
 	struct xarray		personalities;
 	u32			pers_next;
@@ -1135,7 +1135,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	init_waitqueue_head(&ctx->cq_wait);
 	INIT_LIST_HEAD(&ctx->cq_overflow_list);
 	init_completion(&ctx->ref_comp);
-	idr_init(&ctx->io_buffer_idr);
+	xa_init_flags(&ctx->io_buffers, XA_FLAGS_ALLOC1);
 	xa_init_flags(&ctx->personalities, XA_FLAGS_ALLOC1);
 	mutex_init(&ctx->uring_lock);
 	init_waitqueue_head(&ctx->wait);
@@ -2843,7 +2843,7 @@ static struct io_buffer *io_buffer_select(struct io_kiocb *req, size_t *len,
 
 	lockdep_assert_held(&req->ctx->uring_lock);
 
-	head = idr_find(&req->ctx->io_buffer_idr, bgid);
+	head = xa_load(&req->ctx->io_buffers, bgid);
 	if (head) {
 		if (!list_empty(&head->list)) {
 			kbuf = list_last_entry(&head->list, struct io_buffer,
@@ -2851,7 +2851,7 @@ static struct io_buffer *io_buffer_select(struct io_kiocb *req, size_t *len,
 			list_del(&kbuf->list);
 		} else {
 			kbuf = head;
-			idr_remove(&req->ctx->io_buffer_idr, bgid);
+			xa_erase(&req->ctx->io_buffers, bgid);
 		}
 		if (*len > kbuf->len)
 			*len = kbuf->len;
@@ -3892,7 +3892,7 @@ static int __io_remove_buffers(struct io_ring_ctx *ctx, struct io_buffer *buf,
 	}
 	i++;
 	kfree(buf);
-	idr_remove(&ctx->io_buffer_idr, bgid);
+	xa_erase(&ctx->io_buffers, bgid);
 
 	return i;
 }
@@ -3910,7 +3910,7 @@ static int io_remove_buffers(struct io_kiocb *req, unsigned int issue_flags)
 	lockdep_assert_held(&ctx->uring_lock);
 
 	ret = -ENOENT;
-	head = idr_find(&ctx->io_buffer_idr, p->bgid);
+	head = xa_load(&ctx->io_buffers, p->bgid);
 	if (head)
 		ret = __io_remove_buffers(ctx, head, p->bgid, p->nbufs);
 	if (ret < 0)
@@ -3993,21 +3993,14 @@ static int io_provide_buffers(struct io_kiocb *req, unsigned int issue_flags)
 
 	lockdep_assert_held(&ctx->uring_lock);
 
-	list = head = idr_find(&ctx->io_buffer_idr, p->bgid);
+	list = head = xa_load(&ctx->io_buffers, p->bgid);
 
 	ret = io_add_buffers(p, &head);
-	if (ret < 0)
-		goto out;
-
-	if (!list) {
-		ret = idr_alloc(&ctx->io_buffer_idr, head, p->bgid, p->bgid + 1,
-					GFP_KERNEL);
-		if (ret < 0) {
+	if (ret >= 0 && !list) {
+		ret = xa_insert(&ctx->io_buffers, p->bgid, head, GFP_KERNEL);
+		if (ret < 0)
 			__io_remove_buffers(ctx, head, p->bgid, -1U);
-			goto out;
-		}
 	}
-out:
 	if (ret < 0)
 		req_set_fail_links(req);
 
@@ -8333,19 +8326,13 @@ static int io_eventfd_unregister(struct io_ring_ctx *ctx)
 	return -ENXIO;
 }
 
-static int __io_destroy_buffers(int id, void *p, void *data)
-{
-	struct io_ring_ctx *ctx = data;
-	struct io_buffer *buf = p;
-
-	__io_remove_buffers(ctx, buf, id, -1U);
-	return 0;
-}
-
 static void io_destroy_buffers(struct io_ring_ctx *ctx)
 {
-	idr_for_each(&ctx->io_buffer_idr, __io_destroy_buffers, ctx);
-	idr_destroy(&ctx->io_buffer_idr);
+	struct io_buffer *buf;
+	unsigned long index;
+
+	xa_for_each(&ctx->io_buffers, index, buf)
+		__io_remove_buffers(ctx, buf, index, -1U);
 }
 
 static void io_req_cache_free(struct list_head *list, struct task_struct *tsk)