Re: [RFC v1 17/19] ptwrite uprobes / perf tools probe: Add support of ptwrite probes

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The error code from `strbuf_addf` is silently overwritten, hiding memory allocation or formatting failures.
--

commit 1e80616b3ae889174ea132bb4a1470dd0a9429ba
Author: Andi Kleen <ak@kernel.org>

ptwrite uprobes / perf tools probe: Add support of ptwrite probes

This commit adds a --ptwrite option to perf probe to enable trap-free ptwrite
uprobes. These probes write their values into the Intel PT trace stream
instead of entering the kernel.

> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
[ ... ]
> @@ -2260,9 +2262,11 @@ char *synthesize_probe_trace_command(struct probe_trace_event *tev)
>  	if (strbuf_init(&buf, 32) < 0)
>  		return NULL;
>  
> -	if (strbuf_addf(&buf, "%c:%s/%s ", tp->retprobe ? 'r' : 'p',
> -			tev->group, tev->event) < 0)
> -		goto error;
> +	if (tev->ptwrite)
> +		err = strbuf_addf(&buf, "ptw:%s/%s ", tev->group, tev->event);
> +	else
> +		err = strbuf_addf(&buf, "%c:%s/%s ", tp->retprobe ? 'r' : 'p',
> +				  tev->group, tev->event);
>  
>  	if (tev->uprobes)
>  		err = synthesize_uprobe_trace_def(tp, &buf);

[Severity: Medium]
Does this code silently overwrite the error code from strbuf_addf()?

It appears that if memory allocation fails inside the first strbuf_addf(),
the function continues without checking err. The negative error code is
then overwritten by the return value of the subsequent
synthesize_uprobe_trace_def() or synthesize_kprobe_trace_def() call.

Could this lead to a truncated or malformed trace command being synthesized
and sent to the kernel?

> @@ -2274,7 +2278,6 @@ char *synthesize_probe_trace_command(struct probe_trace_event *tev)
>  
>  	if (err >= 0)
>  		ret = strbuf_detach(&buf, NULL);
> -error:
>  	strbuf_release(&buf);
>  	return ret;
>  }

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Sashiko AI review · https://sashiko.dev/#/patchset/20260831150651.1134594-1-ak@kernel.org?part=17