Re: [PATCH v1] perf trace: Fix possible insufficient allocation of argument formats

[Howard Chu <howardchu95@gmail.com>]

Hello,

Forgot to add, there should be:

Fixes: c7b87ce0dd10 ("perf trace: Fix runtime error of index out of bounds")

Thanks,
Howard

On Mon, Mar 24, 2025 at 04:52:45PM -0700, Howard Chu wrote:
> In my previous fix of runtime error(Link:
> https://lore.kernel.org/linux-perf-users/20250122025519.361873-1-howardchu95@gmail.com/),
> I made a mistake of decrementing one unconditionally, regardless of
> whether an extra 'syscall_nr' or 'nr' field was present in
> libtraceevent's tp_format. This may cause perf trace to allocate one
> fewer arg_fmt entry than needed for the accurate representation of syscall
> arguments.
> 
> This patch corrects the mistake by checking the presence of'syscall_nr' or
> 'nr', and adjusting the length of arg_fmt[] accordingly.
> 
> Signed-off-by: Howard Chu <howardchu95@gmail.com>
> ---
>  tools/perf/builtin-trace.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/perf/builtin-trace.c b/tools/perf/builtin-trace.c
> index a102748bd0c9..ad6dad8e2453 100644
> --- a/tools/perf/builtin-trace.c
> +++ b/tools/perf/builtin-trace.c
> @@ -2139,6 +2139,7 @@ static int syscall__read_info(struct syscall *sc, struct trace *trace)
>  	char tp_name[128];
>  	const char *name;
>  	int err;
> +	bool extra_nr = false;
>  
>  	if (sc->nonexistent)
>  		return -EEXIST;
> @@ -2176,20 +2177,22 @@ static int syscall__read_info(struct syscall *sc, struct trace *trace)
>  		return err;
>  	}
>  
> +	sc->args = sc->tp_format->format.fields;
> +	if (!strcmp(sc->args->name, "__syscall_nr") || !strcmp(sc->args->name, "nr"))
> +		extra_nr = true;
>  	/*
>  	 * The tracepoint format contains __syscall_nr field, so it's one more
>  	 * than the actual number of syscall arguments.
>  	 */
> -	if (syscall__alloc_arg_fmts(sc, sc->tp_format->format.nr_fields - 1))
> +	if (syscall__alloc_arg_fmts(sc, sc->tp_format->format.nr_fields - (extra_nr ? 1 : 0)))
>  		return -ENOMEM;
>  
> -	sc->args = sc->tp_format->format.fields;
>  	/*
>  	 * We need to check and discard the first variable '__syscall_nr'
>  	 * or 'nr' that mean the syscall number. It is needless here.
>  	 * So drop '__syscall_nr' or 'nr' field but does not exist on older kernels.
>  	 */
> -	if (sc->args && (!strcmp(sc->args->name, "__syscall_nr") || !strcmp(sc->args->name, "nr"))) {
> +	if (sc->args && extra_nr) {
>  		sc->args = sc->args->next;
>  		--sc->nr_args;
>  	}
> -- 
> 2.45.2
>