Re: [PATCH v3] jfs: jfs_dmap: Validate db_l2nbperpage while mounting

[Dave Kleikamp <dave.kleikamp@oracle.com>]

On 6/20/23 11:47AM, 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.
> 
> Max number of blocks per page = Page size / Min block size
> => log2(Max num_block per page) = log2(Page size / Min block size)
> 				= log2(Page size) - log2(Min block size)
> 
> => Max db_l2nbperpage = L2PSIZE - L2MINBLOCKSIZE

Thanks. Applied to jfs-next.

> 
> Reported-and-tested-by: syzbot+d2cd27dcf8e04b232eb2@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?id=2a70a453331db32ed491f5cbb07e81bf2d225715
> Cc: stable@vger.kernel.org
> Suggested-by: Dave Kleikamp <dave.kleikamp@oracle.com>
> Signed-off-by: Siddh Raman Pant <code@siddh.me>
> ---
> Changes in v3:
> - Fix typo in commit message (number of pages -> number of blocks per page).
> 
> Changes in v2:
> - Fix upper bound as pointed out in v1 by Shaggy.
> - Add an explanation for the same in commit message for completeness.
> 
>   fs/jfs/jfs_dmap.c   | 6 ++++++
>   fs/jfs/jfs_filsys.h | 2 ++
>   2 files changed, 8 insertions(+)
> 
> diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
> index a3eb1e826947..da6a2bc6bf02 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 > L2PSIZE - L2MINBLOCKSIZE) {
> +		err = -EINVAL;
> +		goto err_release_metapage;
> +	}
> +
>   	bmp->db_numag = le32_to_cpu(dbmp_le->dn_numag);
>   	if (!bmp->db_numag) {
>   		err = -EINVAL;
> diff --git a/fs/jfs/jfs_filsys.h b/fs/jfs/jfs_filsys.h
> index b5d702df7111..33ef13a0b110 100644
> --- a/fs/jfs/jfs_filsys.h
> +++ b/fs/jfs/jfs_filsys.h
> @@ -122,7 +122,9 @@
>   #define NUM_INODE_PER_IAG	INOSPERIAG
>   
>   #define MINBLOCKSIZE		512
> +#define L2MINBLOCKSIZE		9
>   #define MAXBLOCKSIZE		4096
> +#define L2MAXBLOCKSIZE		12
>   #define	MAXFILESIZE		((s64)1 << 52)
>   
>   #define JFS_LINK_MAX		0xffffffff