Patch "io_uring: Fix XArray usage in io_uring_add_task_file" has been added to the 5.8-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    io_uring: Fix XArray usage in io_uring_add_task_file

to the 5.8-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     io_uring-fix-xarray-usage-in-io_uring_add_task_file.patch
and it can be found in the queue-5.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From foo@baz Thu Oct 29 01:16:54 PM CET 2020
From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Date: Fri, 9 Oct 2020 13:49:52 +0100
Subject: io_uring: Fix XArray usage in io_uring_add_task_file

From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>

commit 236434c3438c4da3dfbd6aeeab807577b85e951a upstream.

The xas_store() wasn't paired with an xas_nomem() loop, so if it couldn't
allocate memory using GFP_NOWAIT, it would leak the reference to the file
descriptor.  Also the node pointed to by the xas could be freed between
the call to xas_load() under the rcu_read_lock() and the acquisition of
the xa_lock.

It's easier to just use the normal xa_load/xa_store interface here.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
[axboe: fix missing assign after alloc, cur_uring -> tctx rename]
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/io_uring.c |   21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -7929,27 +7929,24 @@ static void io_uring_cancel_task_request
  */
 static int io_uring_add_task_file(struct file *file)
 {
-	if (unlikely(!current->io_uring)) {
+	struct io_uring_task *tctx = current->io_uring;
+
+	if (unlikely(!tctx)) {
 		int ret;
 
 		ret = io_uring_alloc_task_context(current);
 		if (unlikely(ret))
 			return ret;
+		tctx = current->io_uring;
 	}
-	if (current->io_uring->last != file) {
-		XA_STATE(xas, &current->io_uring->xa, (unsigned long) file);
-		void *old;
+	if (tctx->last != file) {
+		void *old = xa_load(&tctx->xa, (unsigned long)file);
 
-		rcu_read_lock();
-		old = xas_load(&xas);
-		if (old != file) {
+		if (!old) {
 			get_file(file);
-			xas_lock(&xas);
-			xas_store(&xas, file);
-			xas_unlock(&xas);
+			xa_store(&tctx->xa, (unsigned long)file, file, GFP_KERNEL);
 		}
-		rcu_read_unlock();
-		current->io_uring->last = file;
+		tctx->last = file;
 	}
 
 	return 0;


Patches currently in stable-queue which might be from willy@xxxxxxxxxxxxx are

queue-5.8/io_uring-convert-advanced-xarray-uses-to-the-normal-api.patch
queue-5.8/io_uring-fix-xarray-usage-in-io_uring_add_task_file.patch
queue-5.8/io_uring-fix-use-of-xarray-in-__io_uring_files_cancel.patch