Re: [PATCH resend v3] bcachefs: Fix NULL pointer dereference in bch2_opt_to_text

[Hongbo Li]

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@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=37186860aa7812b331d5
> Signed-off-by: Mohammed Anees <pvmohammedanees2003@xxxxxxxxx>
> ---
> 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]);