Re: [PATCH] jfs: jfs_dmap: Validate db_l2nbperpage while mounting

[Dave Kleikamp]

On 6/5/23 9:01AM, Siddh Raman Pant wrote:
> In jfs_dmap.c at line 381, BLKTODMAP is used to get a logical block
> number inside dbFree(). db_l2nbperpage, which is the log2 number of
> blocks per page, is passed as an argument to BLKTODMAP which uses it
> for shifting.
>
> Syzbot reported a shift out-of-bounds crash because db_l2nbperpage is
> too big. This happens because the large value is set without any
> validation in dbMount() at line 181.
>
> Thus, make sure that db_l2nbperpage is correct while mounting.
>
> Reported-and-tested-by: syzbot+d2cd27dcf8e04b232eb2@xxxxxxxxxxxxxxxxxxxxxxxxx
> Link: https://syzkaller.appspot.com/bug?id=2a70a453331db32ed491f5cbb07e81bf2d225715
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Siddh Raman Pant <code@xxxxxxxx>
> ---
>   fs/jfs/jfs_dmap.c | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
> index a3eb1e826947..62f058822a3a 100644
> --- a/fs/jfs/jfs_dmap.c
> +++ b/fs/jfs/jfs_dmap.c
> @@ -178,7 +178,13 @@ int dbMount(struct inode *ipbmap)
>   	dbmp_le = (struct dbmap_disk *) mp->data;
>   	bmp->db_mapsize = le64_to_cpu(dbmp_le->dn_mapsize);
>   	bmp->db_nfree = le64_to_cpu(dbmp_le->dn_nfree);
> +
>   	bmp->db_l2nbperpage = le32_to_cpu(dbmp_le->dn_l2nbperpage);
> +	if (bmp->db_l2nbperpage > L2MAXL0SIZE) {

Actually the sanity check should be much smaller. The maximum value 
should be L2PSIZE - log2(MINBLOCKSIZE). In reality, I think it's always 
zero.

Shaggy

> +		err = -EINVAL;
> +		goto err_release_metapage;
> +	}
> +
>   	bmp->db_numag = le32_to_cpu(dbmp_le->dn_numag);
>   	if (!bmp->db_numag) {
>   		err = -EINVAL;