linux-kernel - Re: [PATCH v2] bcachefs: Fix NULL pointer dereference in bch2_opt_to

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Message-ID: <kipwon7rswbzlyafdkbnhmv2qy2rvgdifrjjtokm7zz5pll4ur@wwkxb4c4scs5>
Date: Sat, 21 Sep 2024 19:41:26 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Mohammed Anees <pvmohammedanees2003@...il.com>
Cc: linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org, 
	syzbot+37186860aa7812b331d5@...kaller.appspotmail.com
Subject: Re: [PATCH v2] bcachefs: Fix NULL pointer dereference in
 bch2_opt_to_text

On Sat, Sep 21, 2024 at 11:24:54PM GMT, Mohammed Anees wrote:
> In this patch, I added a proper bounds check to avoid a potential NULL
> pointer dereference when opt->choices[v] is accessed in the
> bch2_opt_to_text function. This ensures that v is within the valid
> range of choices.
> 
> Reported-and-tested-by: syzbot+37186860aa7812b331d5@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=37186860aa7812b331d5
> Signed-off-by: Mohammed Anees <pvmohammedanees2003@...il.com>
> ---
> 
> v2:
> - Replaced pr_err with prt_printf as suggested.
> - Added the bounds check on opt->choices before accessing it.
> 
>  fs/bcachefs/opts.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/bcachefs/opts.c b/fs/bcachefs/opts.c
> index e10fc1da7..9bb15694d 100644
> --- a/fs/bcachefs/opts.c
> +++ b/fs/bcachefs/opts.c
> @@ -420,8 +420,12 @@ void bch2_opt_to_text(struct printbuf *out,
>  	case BCH_OPT_STR:
>  		if (flags & OPT_SHOW_FULL_LIST)
>  			prt_string_option(out, opt->choices, v);
> -		else
> -			prt_str(out, opt->choices[v]);
> +		else {
> +			if (v < opt->min || v >= opt->max - 1)
> +				prt_printf(out, "(invalid option %lli)", v);
> +			else
> +				prt_str(out, opt->choices[v]);
> +		}

For consistency, the bounds check should come first (applying in the
OPT_SHOW_FULL_LIST case as well) - also, kill the nested if clauses,
this all works with chained if else.

Sorry for dribbling out the review feedback, that should be
everything...