linux-kernel - Re: KASAN: null-ptr-deref Write in get

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Date:   Mon, 23 Mar 2020 14:42:25 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Qiujun Huang <anenbupt@...il.com>
Cc:     syzbot <syzbot+4a88b2b9dc280f47baf4@...kaller.appspotmail.com>,
        aeb@....nl, danarag@...il.com, kstewart@...uxfoundation.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        tglx@...utronix.de, viro@...iv.linux.org.uk
Subject: Re: KASAN: null-ptr-deref Write in get_block

Fix the subject to [PATCH] minix: Fix NULL dereference in alloc_branch()

On Sun, Mar 22, 2020 at 08:06:48PM +0800, Qiujun Huang wrote:
> Need to check the return value of sb_getblk.
> 

Add a Reported-by tag.

Reported-by: syzbot+4a88b2b9dc280f47baf4@...kaller.appspotmail.com

> Signed-off-by: Qiujun Huang <hqjagain@...il.com>
> ---
>  fs/minix/itree_common.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/minix/itree_common.c b/fs/minix/itree_common.c
> index 043c3fd..eedd79f 100644
> --- a/fs/minix/itree_common.c
> +++ b/fs/minix/itree_common.c
> @@ -85,6 +85,8 @@ static int alloc_branch(struct inode *inode,
>   break;
>   branch[n].key = cpu_to_block(nr);
>   bh = sb_getblk(inode->i_sb, parent);
> + if (!bh)
> + break;

The patch is white space damaged and we need to do a bit of error
handling before the break as well.

 	bh = sb_getblk(inode->i_sb, parent);
+	if (!bh) {
+		minix_free_block(inode, block_to_cpu(branch[n].key));
+		break;
+	}
 	lock_buffer(bh);

Please fix those few things and resend.

regards,
dan carpenter