linux-kernel - [PATCH] fuse: Fix a potential double free in virtio_fs_get

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Message-Id: <20210323051831.13575-1-lyl2019@mail.ustc.edu.cn>
Date:   Mon, 22 Mar 2021 22:18:31 -0700
From:   Lv Yunlong <lyl2019@...l.ustc.edu.cn>
To:     vgoyal@...hat.com, stefanha@...hat.com, miklos@...redi.hu
Cc:     virtualization@...ts.linux-foundation.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Lv Yunlong <lyl2019@...l.ustc.edu.cn>
Subject: [PATCH] fuse: Fix a potential double free in virtio_fs_get_tree

In virtio_fs_get_tree, fm is allocated by kzalloc() and
assigned to fsc->s_fs_info by fsc->s_fs_info=fm statement.
If the kzalloc() failed, it will goto err directly, so that
fsc->s_fs_info must be non-NULL and fm will be freed.

But later fm is freed again when virtio_fs_fill_super() fialed.
I think the statement if (fsc->s_fs_info) {kfree(fm);} is
misplaced.

My patch puts this statement in the correct palce to avoid
double free.

Signed-off-by: Lv Yunlong <lyl2019@...l.ustc.edu.cn>
---
 fs/fuse/virtio_fs.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
index 8868ac31a3c0..727cf436828f 100644
--- a/fs/fuse/virtio_fs.c
+++ b/fs/fuse/virtio_fs.c
@@ -1437,10 +1437,7 @@ static int virtio_fs_get_tree(struct fs_context *fsc)
 
 	fsc->s_fs_info = fm;
 	sb = sget_fc(fsc, virtio_fs_test_super, set_anon_super_fc);
-	if (fsc->s_fs_info) {
-		fuse_conn_put(fc);
-		kfree(fm);
-	}
+
 	if (IS_ERR(sb))
 		return PTR_ERR(sb);
 
@@ -1457,6 +1454,11 @@ static int virtio_fs_get_tree(struct fs_context *fsc)
 		sb->s_flags |= SB_ACTIVE;
 	}
 
+	if (fsc->s_fs_info) {
+		fuse_conn_put(fc);
+		kfree(fm);
+	}
+
 	WARN_ON(fsc->root);
 	fsc->root = dget(sb->s_root);
 	return 0;
-- 
2.25.1