linux-kernel - Re: [RFC tracing 1/4] tracing: predicate matching trigger crashes for

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Message-ID: <20220807185220.6aaa0593@rorschach.local.home>
Date:   Sun, 7 Aug 2022 18:53:13 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alan Maguire <alan.maguire@...cle.com>
Cc:     corbet@....net, mingo@...hat.com, shuah@...nel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [RFC tracing 1/4] tracing: predicate matching trigger crashes
 for > 8-byte arrays

On Sun,  7 Aug 2022 23:21:20 +0100
Alan Maguire <alan.maguire@...cle.com> wrote:

> The following (wrong) use of tracepoint filtering was enough to trigger
> a null-pointer dereference crash:
> 
> 	cd /sys/kernel/debug/tracing
> 	echo "saddr_v6 == 0x0100007f" > tcp/tcp_receive_reset/filter
> 	echo 1 > tcp/tcp_receive_reset/enable
> 	wget https://localhost
> 
> This works fine if saddr - a 4-byte array representing the source address -
> is used instead.
> 

The patch series is a new feature so it would need to go into the next
merge window. But this patch looks to be a bug fix, so I'll pull this
one in separately, and tag it for stable.

Thanks,

-- Steve


> Fix is to handle case where we encounter an unexpected size.
> 
> Signed-off-by: Alan Maguire <alan.maguire@...cle.com>
> ---
>  kernel/trace/trace_events_filter.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
> index 4b1057ab9d96..65e01c8d48d9 100644
> --- a/kernel/trace/trace_events_filter.c
> +++ b/kernel/trace/trace_events_filter.c
> @@ -1490,6 +1490,11 @@ static int parse_pred(const char *str, void *data,
>  		else {
>  			pred->fn = select_comparison_fn(pred->op, field->size,
>  							field->is_signed);
> +			if (!pred->fn) {
> +				parse_error(pe, FILT_ERR_ILLEGAL_FIELD_OP,
> +					    pos + i);
> +				goto err_free;
> +			}
>  			if (pred->op == OP_NE)
>  				pred->not = 1;
>  		}