Re: [PATCH] hfsplus: don't return 0 when fill_super() failed

["Ernesto A. Fernández" <ernesto.mnd.fernandez@gmail.com>]

On Tue, May 15, 2018 at 07:08:24PM +0900, Tetsuo Handa wrote:
> From f78a5fe168290cb9e009f4d907d04b5bfe277831 Mon Sep 17 00:00:00 2001
> From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Date: Tue, 15 May 2018 11:38:38 +0900
> Subject: [PATCH] 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
> 
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Reported-by: syzbot <syzbot+01ffaf5d9568dd1609f7@syzkaller.appspotmail.com>
> Cc: Al Viro <viro@zeniv.linux.org.uk>

It's been too long. I think I should give up on my patch. Maybe a review
can help your version get merged.

Reviewed-by: Ernesto A. Fernández <ernesto.mnd.fernandez@gmail.com>

> ---
>  fs/hfsplus/super.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/hfsplus/super.c b/fs/hfsplus/super.c
> index 513c357..9e690ae 100644
> --- 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);
> -- 
> 1.8.3.1
> 
>