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 <clo...@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.

Best,
Carlos

Thank you,

Fixes: c440adfbe3025 ("tracing/probes: Support BTF based data structure field 
access")
Signed-off-by: Carlos López <clo...@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