Re: [PATCH v2] fs/jfs: Add check for negative db_l2nbperpage

[Dave Kleikamp]

On 10/2/23 4:56AM, Juntong Deng wrote:
> l2nbperpage is log2(number of blks per page), and the minimum legal
> value should be 0, not negative.
>
> In the case of l2nbperpage being negative, an error will occur
> when subsequently used as shift exponent.
>
> Syzbot reported this bug:
>
> UBSAN: shift-out-of-bounds in fs/jfs/jfs_dmap.c:799:12
> shift exponent -16777216 is negative

Looks good. (A little part of me wants to go through the code and make a 
lot of signed ints unsigned, but not today.)

Applied to jfs-next

Thanks,
Shaggy

> Reported-by: syzbot+debee9ab7ae2b34b0307@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=debee9ab7ae2b34b0307
> Signed-off-by: Juntong Deng <juntong.deng@xxxxxxxxxxx>
> ---
>   fs/jfs/jfs_dmap.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
> index 88afd108c2dd..3a1842348112 100644
> --- a/fs/jfs/jfs_dmap.c
> +++ b/fs/jfs/jfs_dmap.c
> @@ -180,7 +180,8 @@ int dbMount(struct inode *ipbmap)
>   	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) {
> +	if (bmp->db_l2nbperpage > L2PSIZE - L2MINBLOCKSIZE ||
> +		bmp->db_l2nbperpage < 0) {
>   		err = -EINVAL;
>   		goto err_release_metapage;
>   	}