linux-kernel - Re: [PATCH v2] fs/jfs: Add check for negative db

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Message-ID: <c943f428-3759-4922-9622-fd481d0ac26d@oracle.com>
Date:   Tue, 3 Oct 2023 18:27:45 -0500
From:   Dave Kleikamp <dave.kleikamp@...cle.com>
To:     Juntong Deng <juntong.deng@...look.com>, shaggy@...nel.org,
        wonguk.lee1023@...il.com, liushixin2@...wei.com,
        andrew.kanner@...il.com, wuhoipok@...il.com
Cc:     jfs-discussion@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        syzbot+debee9ab7ae2b34b0307@...kaller.appspotmail.com
Subject: Re: [PATCH v2] fs/jfs: Add check for negative db_l2nbperpage

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@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=debee9ab7ae2b34b0307
> Signed-off-by: Juntong Deng <juntong.deng@...look.com>
> ---
>   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;
>   	}