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

[Carlos López]

Hi,

On 26/5/24 12:17, Masami Hiramatsu (Google) wrote:
> On Sat, 25 May 2024 20:21:32 +0200
> Carlos López <clopez@xxxxxxx> 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.

Best,
Carlos

> Thank you,
>
> > Fixes: c440adfbe3025 ("tracing/probes: Support BTF based data structure field access")
> > Signed-off-by: Carlos López <clopez@xxxxxxx>
> > ---
> >   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