Re: [PATCH] tracing/probes: fix error check in parse_btf_field()

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Sun, 26 May 2024 14:27:56 +0200
Carlos López <clopez@suse.de> wrote:

> 
> Hi,
> 
> On 26/5/24 12:17, Masami Hiramatsu (Google) wrote:
> > On Sat, 25 May 2024 20:21:32 +0200
> > Carlos López <clopez@suse.de> wrote:
> > 
> >> btf_find_struct_member() might return NULL or an error via the
> >> ERR_PTR() macro. However, its caller in parse_btf_field() only checks
> >> for the NULL condition. Fix this by using IS_ERR() and returning the
> >> error up the stack.
> >>
> > 
> > Thanks for finding it!
> > I think this requires new error message for error_log file.
> > Can you add the log as
> > 
> > trace_probe_log_err(ctx->offset, BTF_ERROR);
> > 
> > And define BTF_ERROR in ERRORS@kernel/trace/trace_probe.h ?
> 
> Sounds good, but should we perhaps reuse BAD_BTF_TID?
> 
> ```
> C(BAD_BTF_TID,		"Failed to get BTF type info."),\
> ```
> 
> `btf_find_struct_member()` fails if `type` is not a struct or if it runs
> OOM while allocating the anon stack, so it seems appropriate.

Good point, it sounds reasonable.

Thanks!

> 
> Best,
> Carlos
> 
> > Thank you,
> > 
> >> Fixes: c440adfbe3025 ("tracing/probes: Support BTF based data structure field access")
> >> Signed-off-by: Carlos López <clopez@suse.de>
> >> ---
> >>   kernel/trace/trace_probe.c | 2 ++
> >>   1 file changed, 2 insertions(+)
> >>
> >> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> >> index 5e263c141574..5417e9712157 100644
> >> --- a/kernel/trace/trace_probe.c
> >> +++ b/kernel/trace/trace_probe.c
> >> @@ -554,6 +554,8 @@ static int parse_btf_field(char *fieldname, const struct btf_type *type,
> >>   			anon_offs = 0;
> >>   			field = btf_find_struct_member(ctx->btf, type, fieldname,
> >>   						       &anon_offs);
> >> +			if (IS_ERR(field))
> >> +				return PTR_ERR(field);
> >>   			if (!field) {
> >>   				trace_probe_log_err(ctx->offset, NO_BTF_FIELD);
> >>   				return -ENOENT;
> >> -- 
> >> 2.35.3
> >>
> > 
> > 
> 
> -- 
> Carlos López
> Security Engineer
> SUSE Software Solutions


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>