[PATCH 09/13] perf bpf: Validate func_info_rec_size and sub_id in synthesize_bpf_prog_name()

[Arnaldo Carvalho de Melo]

From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

synthesize_bpf_prog_name() computes a pointer into the func_info array
using sub_id * info->func_info_rec_size without validating either value.
Both come from perf.data and are untrusted:

- A func_info_rec_size smaller than sizeof(struct bpf_func_info) means
  the finfo pointer would reference a truncated entry, reading past it
  into adjacent data.

- A sub_id >= nr_func_info computes an offset past the func_info buffer,
  causing an out-of-bounds read.

Add bounds checks for both values before computing the pointer offset.
When validation fails, fall through to the non-BTF name path instead
of reading garbage.

Reported-by: sashiko-bot <sashiko-bot@xxxxxxxxxx>
Fixes: 7b612e291a5affb1 ("perf tools: Synthesize PERF_RECORD_* for loaded BPF programs")
Cc: Song Liu <songliubraving@xxxxxx>
Assisted-by: Claude Opus 4.6 <noreply@xxxxxxxxxxxxx>
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/bpf-event.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/bpf-event.c b/tools/perf/util/bpf-event.c
index c4594969d7677238..fe6fbca508c5135c 100644
--- a/tools/perf/util/bpf-event.c
+++ b/tools/perf/util/bpf-event.c
@@ -143,7 +143,9 @@ static int synthesize_bpf_prog_name(char *buf, int size,
 	name_len = scnprintf(buf, size, "bpf_prog_");
 	name_len += snprintf_hex(buf + name_len, size - name_len,
 				 prog_tags[sub_id], BPF_TAG_SIZE);
-	if (btf) {
+	if (btf &&
+	    info->func_info_rec_size >= sizeof(*finfo) &&
+	    sub_id < info->nr_func_info) {
 		finfo = func_infos + sub_id * info->func_info_rec_size;
 		t = btf__type_by_id(btf, finfo->type_id);
 		if (t)
-- 
2.54.0