linux-kernel - Re: [PATCH v2] ntfs: Ensure $Extend is a directory

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Date:   Mon, 29 Aug 2022 08:03:10 -0700
From:   Soumya Negi <soumya.negi97@...il.com>
To:     Anton Altaparmakov <anton@...era.com>,
        Shuah Khan <skhan@...uxfoundation.org>
Cc:     linux-ntfs-dev@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] ntfs: Ensure $Extend is a directory

On Tue, Jul 26, 2022 at 05:15:13PM -0700, Soumya Negi wrote:
> Fix Syzbot bug: kernel BUG in ntfs_lookup_inode_by_name
> https://syzkaller.appspot.com/bug?id=32cf53b48c1846ffc25a185a2e92e170d1a95d71
> 
> Check whether $Extend is a directory or not( for NTFS3.0+) while
> loading system files. If it isn't(as in the case of this bug where the
> mft record for $Extend contains a regular file), load_system_files()
> returns false.
> 
> Reported-by: syzbot+30b7f850c6d98ea461d2@...kaller.appspotmail.com
> CC: stable@...r.kernel.org # 4.9+
> Signed-off-by: Soumya Negi <soumya.negi97@...il.com>
> ---
> Changes since v1:
> * Added CC tag for stable
> * Formatted changelog to fit within 72 cols
> 
> ---
>  fs/ntfs/super.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ntfs/super.c b/fs/ntfs/super.c
> index 5ae8de09b271..18e2902531f9 100644
> --- a/fs/ntfs/super.c
> +++ b/fs/ntfs/super.c
> @@ -2092,10 +2092,15 @@ static bool load_system_files(ntfs_volume *vol)
>  	// TODO: Initialize security.
>  	/* Get the extended system files' directory inode. */
>  	vol->extend_ino = ntfs_iget(sb, FILE_Extend);
> -	if (IS_ERR(vol->extend_ino) || is_bad_inode(vol->extend_ino)) {
> +	if (IS_ERR(vol->extend_ino) || is_bad_inode(vol->extend_ino) ||
> +	    !S_ISDIR(vol->extend_ino->i_mode)) {
> +		static const char *es1 = "$Extend is not a directory";
> +		static const char *es2 = "Failed to load $Extend";
> +		const char *es = !S_ISDIR(vol->extend_ino->i_mode) ? es1 : es2;
> +
>  		if (!IS_ERR(vol->extend_ino))
>  			iput(vol->extend_ino);
> -		ntfs_error(sb, "Failed to load $Extend.");
> +		ntfs_error(sb, "%s.", es);
>  		goto iput_sec_err_out;
>  	}
>  #ifdef NTFS_RW
> -- 
> 2.17.1

Hi Anton,
Have you had a chance to look at this patch?

Thanks,
Soumya