hfsplus: don't return 0 when fill_super() failed

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@I-love.SAKURA.ne.jp
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-by: syzbot <syzbot+01ffaf5d9568dd1609f7@syzkaller.appspotmail.com>
Reviewed-by: Ernesto A. Fernández <ernesto.mnd.fernandez@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/hfsplus/super.c b/fs/hfsplus/super.c
index a6c0f54..80abba5 100644 (file)
--- a/fs/hfsplus/super.c
+++ b/fs/hfsplus/super.c
@@ -524,8 +524,10 @@ static int hfsplus_fill_super(struct super_block *sb, void *data, int silent)
                goto out_put_root;
        if (!hfs_brec_read(&fd, &entry, sizeof(entry))) {
                hfs_find_exit(&fd);
-               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);