linux-kernel - Re: [PATCH] Null check to prevent null-ptr-deref bug

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Message-ID: <2023052803-pucker-depress-5452@gregkh>
Date:   Sun, 28 May 2023 07:58:23 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Prince Kumar Maurya <princekumarmaurya06@...il.com>
Cc:     skhan@...uxfoundation.org, viro@...iv.linux.org.uk,
        brauner@...nel.org, chenzhongjin@...wei.com,
        syzkaller-bugs@...glegroups.com,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Null check to prevent null-ptr-deref bug

On Sat, May 27, 2023 at 06:25:16PM -0700, Prince Kumar Maurya wrote:
> sb_getblk(inode->i_sb, parent) return a null ptr and taking lock on that leads to the null-ptr-deref bug.

Please wrap your changelog comments at 72 columns.

> Signed-off-by: Prince Kumar Maurya <princekumarmaurya06@...il.com>
> ---
>  fs/sysv/itree.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/sysv/itree.c b/fs/sysv/itree.c
> index b22764fe669c..3a6b66e719fd 100644
> --- a/fs/sysv/itree.c
> +++ b/fs/sysv/itree.c
> @@ -145,6 +145,8 @@ static int alloc_branch(struct inode *inode,
>  		 */
>  		parent = block_to_cpu(SYSV_SB(inode->i_sb), branch[n-1].key);
>  		bh = sb_getblk(inode->i_sb, parent);
> +		if (!bh)
> +			break;

How have you tested this?  Have you reproduced this failure and has this
patch resolved the issue?  This function should never really fail in
normal operation, so it's odd that you were able to hit this somehow.

thanks,

greg k-h