linux-kernel - [PATCH] fs: btrfs: fix possible use-after-free bug in error handling code of btrfs_get_root

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Date:   Thu, 24 Mar 2022 06:44:54 -0700
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     clm@...com, josef@...icpanda.com, dsterba@...e.com
Cc:     linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jia-Ju Bai <baijiaju1990@...il.com>
Subject: [PATCH] fs: btrfs: fix possible use-after-free bug in error handling code of btrfs_get_root_ref()

In btrfs_get_root_ref(), when btrfs_insert_fs_root() fails,
btrfs_put_root() will be called to possibly free the memory area of
the variable root. However, this variable is then used again in error
handling code after "goto fail", when ret is not -EEXIST.

To fix this possible bug, btrfs_put_root() is only called when ret is 
-EEXIST for "goto again".

Reported-by: TOTE Robot <oslab@...nghua.edu.cn>
Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
---
 fs/btrfs/disk-io.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index b30309f187cf..126f244cdf88 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1850,9 +1850,10 @@ static struct btrfs_root *btrfs_get_root_ref(struct btrfs_fs_info *fs_info,
 
 	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;
-- 
2.17.1