linux-kernel - [PATCH 5.15 156/189] btrfs: fix root ref counts in error handling in btrfs_get_root

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Message-Id: <20220418121206.544212252@linuxfoundation.org>
Date:   Mon, 18 Apr 2022 14:12:56 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, TOTE Robot <oslab@...nghua.edu.cn>,
        Jia-Ju Bai <baijiaju1990@...il.com>,
        David Sterba <dsterba@...e.com>
Subject: [PATCH 5.15 156/189] btrfs: fix root ref counts in error handling in btrfs_get_root_ref

From: Jia-Ju Bai <baijiaju1990@...il.com>

commit 168a2f776b9762f4021421008512dd7ab7474df1 upstream.

In btrfs_get_root_ref(), when btrfs_insert_fs_root() fails,
btrfs_put_root() can happen for two reasons:

- the root already exists in the tree, in that case it returns the
  reference obtained in btrfs_lookup_fs_root()

- another error so the cleanup is done in the fail label

Calling btrfs_put_root() unconditionally would lead to double decrement
of the root reference possibly freeing it in the second case.

Reported-by: TOTE Robot <oslab@...nghua.edu.cn>
Fixes: bc44d7c4b2b1 ("btrfs: push btrfs_grab_fs_root into btrfs_get_fs_root")
CC: stable@...r.kernel.org # 5.10+
Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
Reviewed-by: David Sterba <dsterba@...e.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/btrfs/disk-io.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1738,9 +1738,10 @@ again:
 
 	ret = btrfs_insert_fs_root(fs_info, root);
 	if (ret) {
-		btrfs_put_root(root);
-		if (ret == -EEXIST)
+		if (ret == -EEXIST) {
+			btrfs_put_root(root);
 			goto again;
+		}
 		goto fail;
 	}
 	return root;