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[PATCH 4.9 17/78] hfsplus: dont return 0 when fill_super() failed

4.9-stable review patch.  If anyone has any objections, please let me know.


From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>

[ Upstream commit 7464726cb5998846306ed0a7d6714afb2e37b25d ]

syzbot is reporting NULL pointer dereference at mount_fs() [1].  This is
because hfsplus_fill_super() is by error returning 0 when
hfsplus_fill_super() detected invalid filesystem image, and mount_bdev()
is returning NULL because dget(s->s_root) == NULL if s->s_root == NULL,
and mount_fs() is accessing root->d_sb because IS_ERR(root) == false if
root == NULL.  Fix this by returning -EINVAL when hfsplus_fill_super()
detected invalid filesystem image.

[1] https://syzkaller.appspot.com/bug?id=21acb6850cecbc960c927229e597158cf35f33d0

Link: http://lkml.kernel.org/r/d83ce31a-874c-dd5b-f790-41405983a5be@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Reported-by: syzbot <syzbot+01ffaf5d9568dd1609f7@xxxxxxxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Ernesto A. Fernández <ernesto.mnd.fernandez@xxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
 fs/hfsplus/super.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/fs/hfsplus/super.c
+++ b/fs/hfsplus/super.c
@@ -524,8 +524,10 @@ static int hfsplus_fill_super(struct sup
 		goto out_put_root;
 	if (!hfs_brec_read(&fd, &entry, sizeof(entry))) {
-		if (entry.type != cpu_to_be16(HFSPLUS_FOLDER))
+		if (entry.type != cpu_to_be16(HFSPLUS_FOLDER)) {
+			err = -EINVAL;
 			goto out_put_root;
+		}
 		inode = hfsplus_iget(sb, be32_to_cpu(entry.folder.id));
 		if (IS_ERR(inode)) {
 			err = PTR_ERR(inode);