linux-kernel - Re: [PATCH v2] hfs: Sanity check the root record

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Message-ID: <20241202122425.rlxuge77wq7iiz6w@quack3>
Date: Mon, 2 Dec 2024 13:24:25 +0100
From: Jan Kara <jack@...e.cz>
To: Leo Stone <leocstone@...il.com>
Cc: brauner@...nel.org, sandeen@...hat.com, jack@...e.cz,
	viro@...iv.linux.org.uk, quic_jjohnson@...cinc.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	syzbot+2db3c7526ba68f4ea776@...kaller.appspotmail.com
Subject: Re: [PATCH v2] hfs: Sanity check the root record

On Sat 30-11-24 21:14:19, Leo Stone wrote:
> In the syzbot reproducer, the hfs_cat_rec for the root dir has type
> HFS_CDR_FIL after being read with hfs_bnode_read() in hfs_super_fill().
> This indicates it should be used as an hfs_cat_file, which is 102 bytes.
> Only the first 70 bytes of that struct are initialized, however,
> because the entrylength passed into hfs_bnode_read() is still the length of
> a directory record. This causes uninitialized values to be used later on,
> when the hfs_cat_rec union is treated as the larger hfs_cat_file struct.
> 
> Add a check to make sure the retrieved record has the correct type
> for the root directory (HFS_CDR_DIR), and make sure we load the correct
> number of bytes for a directory record.
> 
> Reported-by: syzbot+2db3c7526ba68f4ea776@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=2db3c7526ba68f4ea776
> Tested-by: syzbot+2db3c7526ba68f4ea776@...kaller.appspotmail.com
> Tested-by: Leo Stone <leocstone@...il.com>
> Signed-off-by: Leo Stone <leocstone@...il.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza
> ---
> v2: Made the check on fd.entrylength more strict. Tested with real HFS
>     images.
> v1: https://lore.kernel.org/all/20241123194949.9243-1-leocstone@gmail.com
> ---
>  fs/hfs/super.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/hfs/super.c b/fs/hfs/super.c
> index 3bee9b5dba5e..fe09c2093a93 100644
> --- a/fs/hfs/super.c
> +++ b/fs/hfs/super.c
> @@ -349,11 +349,13 @@ static int hfs_fill_super(struct super_block *sb, struct fs_context *fc)
>  		goto bail_no_root;
>  	res = hfs_cat_find_brec(sb, HFS_ROOT_CNID, &fd);
>  	if (!res) {
> -		if (fd.entrylength > sizeof(rec) || fd.entrylength < 0) {
> +		if (fd.entrylength != sizeof(rec.dir)) {
>  			res =  -EIO;
>  			goto bail_hfs_find;
>  		}
>  		hfs_bnode_read(fd.bnode, &rec, fd.entryoffset, fd.entrylength);
> +		if (rec.type != HFS_CDR_DIR)
> +			res = -EIO;
>  	}
>  	if (res)
>  		goto bail_hfs_find;
> -- 
> 2.43.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR