linux-kernel - Re: [PATCH v2] fs: jfs: fix shift-out-of-bounds in dbAllocAG

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Date:   Mon, 17 Oct 2022 15:02:02 -0500
From:   Dave Kleikamp <dave.kleikamp@...cle.com>
To:     Dongliang Mu <dzm91@...t.edu.cn>
Cc:     Dongliang Mu <mudongliangabcd@...il.com>,
        syzbot+15342c1aa6a00fb7a438@...kaller.appspotmail.com,
        jfs-discussion@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] fs: jfs: fix shift-out-of-bounds in dbAllocAG

Looks good. Pushed to jfs-next.

Thanks,
Shaggy

On 10/15/22 8:25PM, Dongliang Mu wrote:
> From: Dongliang Mu <mudongliangabcd@...il.com>
> 
> Syzbot found a crash : UBSAN: shift-out-of-bounds in dbAllocAG. The
> underlying bug is the missing check of bmp->db_agl2size. The field can
> be greater than 64 and trigger the shift-out-of-bounds.
> 
> Fix this bug by adding a check of bmp->db_agl2size in dbMount since this
> field is used in many following functions. The upper bound for this
> field is MAXMAPSIZE - L2MAXAG, thanks for the help of Dave Kleikamp.
> Notethat, for maintainance, I reorganzie error handling code of dbMount.
> 
> Reported-by: syzbot+15342c1aa6a00fb7a438@...kaller.appspotmail.com
> Signed-off-by: Dongliang Mu <mudongliangabcd@...il.com>
> ---
> v1->2: fix the size of bmp->db_agl2size; revise the correct upper bound
>   fs/jfs/jfs_dmap.c | 22 ++++++++++++++++------
>   1 file changed, 16 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
> index 6b838d3ae7c2..962c855631cb 100644
> --- a/fs/jfs/jfs_dmap.c
> +++ b/fs/jfs/jfs_dmap.c
> @@ -155,7 +155,7 @@ int dbMount(struct inode *ipbmap)
>   	struct bmap *bmp;
>   	struct dbmap_disk *dbmp_le;
>   	struct metapage *mp;
> -	int i;
> +	int i, err;
>   
>   	/*
>   	 * allocate/initialize the in-memory bmap descriptor
> @@ -170,8 +170,8 @@ int dbMount(struct inode *ipbmap)
>   			   BMAPBLKNO << JFS_SBI(ipbmap->i_sb)->l2nbperpage,
>   			   PSIZE, 0);
>   	if (mp == NULL) {
> -		kfree(bmp);
> -		return -EIO;
> +		err = -EIO;
> +		goto err_kfree_bmp;
>   	}
>   
>   	/* copy the on-disk bmap descriptor to its in-memory version. */
> @@ -181,9 +181,8 @@ int dbMount(struct inode *ipbmap)
>   	bmp->db_l2nbperpage = le32_to_cpu(dbmp_le->dn_l2nbperpage);
>   	bmp->db_numag = le32_to_cpu(dbmp_le->dn_numag);
>   	if (!bmp->db_numag) {
> -		release_metapage(mp);
> -		kfree(bmp);
> -		return -EINVAL;
> +		err = -EINVAL;
> +		goto err_release_metapage;
>   	}
>   
>   	bmp->db_maxlevel = le32_to_cpu(dbmp_le->dn_maxlevel);
> @@ -194,6 +193,11 @@ int dbMount(struct inode *ipbmap)
>   	bmp->db_agwidth = le32_to_cpu(dbmp_le->dn_agwidth);
>   	bmp->db_agstart = le32_to_cpu(dbmp_le->dn_agstart);
>   	bmp->db_agl2size = le32_to_cpu(dbmp_le->dn_agl2size);
> +	if (bmp->db_agl2size > MAXMAPSIZE - L2MAXAG) {
> +		err = -EINVAL;
> +		goto err_release_metapage;
> +	}
> +
>   	for (i = 0; i < MAXAG; i++)
>   		bmp->db_agfree[i] = le64_to_cpu(dbmp_le->dn_agfree[i]);
>   	bmp->db_agsize = le64_to_cpu(dbmp_le->dn_agsize);
> @@ -214,6 +218,12 @@ int dbMount(struct inode *ipbmap)
>   	BMAP_LOCK_INIT(bmp);
>   
>   	return (0);
> +
> +err_release_metapage:
> +	release_metapage(mp);
> +err_kfree_bmp:
> +	kfree(bmp);
> +	return err;
>   }
>   
>