linux-kernel - Re: [PATCH resend v3] bcachefs: Fix NULL pointer dereference in bch2_opt_to

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Message-ID: <f8fcc1e6-6de6-4d60-83a7-83e95a7d6b6e@huawei.com>
Date: Tue, 8 Oct 2024 10:23:08 +0800
From: Hongbo Li <lihongbo22@...wei.com>
To: Mohammed Anees <pvmohammedanees2003@...il.com>, Kent Overstreet
	<kent.overstreet@...ux.dev>
CC: <syzbot+37186860aa7812b331d5@...kaller.appspotmail.com>, LKML
	<linux-kernel@...r.kernel.org>, "linux-bcachefs@...r.kernel.org"
	<linux-bcachefs@...r.kernel.org>
Subject: Re: [PATCH resend v3] bcachefs: Fix NULL pointer dereference in
 bch2_opt_to_text



On 2024/10/5 21:02, Mohammed Anees wrote:
> This patch adds a bounds check to the bch2_opt_to_text function to prevent
> NULL pointer dereferences when accessing the opt->choices array. This
> ensures that the index used is within valid bounds before dereferencing.
> The new version enhances the readability.
> 
> 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>
> ---
> v3:
> - Moved bounds check above as default case.
> - Removed the nesterd if clauses.
> ---
>   fs/bcachefs/opts.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/bcachefs/opts.c b/fs/bcachefs/opts.c
> index 232be8a44051..84097235eea9 100644
> --- a/fs/bcachefs/opts.c
> +++ b/fs/bcachefs/opts.c
> @@ -427,7 +427,9 @@ void bch2_opt_to_text(struct printbuf *out,
>   			prt_printf(out, "%lli", v);
>   		break;
>   	case BCH_OPT_STR:
> -		if (flags & OPT_SHOW_FULL_LIST)
> +		if (v < opt->min || v >= opt->max - 1)
As definition, max is the right bound for value. opt->max - 1 is valid. 
May be you should remove the equals sign.

It should be no problem to just solve this null pointer issue() (How is 
this stack triggered, may be I lost something.), but this should be a 
general boundary check condition, strictly speaking, it's a check for 
the validity of the options' value.

Thanks,
Hongbo

> +			prt_printf(out, "(invalid option %lli)", v);
> +		else if (flags & OPT_SHOW_FULL_LIST)
>   			prt_string_option(out, opt->choices, v);
>   		else
>   			prt_str(out, opt->choices[v]);