[PATCH v5 2/8] perf bpf-filter: Fix bpf_link leak by using PERF_EVENT_IOC_SET_BPF

[Ian Rogers]

In perf_bpf_filter__prepare(), the unpinned filter path attaches
skel->progs.perf_sample_filter to each FD(evsel, x, y) using
bpf_program__attach_perf_event_opts() and ignores the returned
struct bpf_link *, leaking the allocated struct bpf_link_perf and its
BPF_PERF_EVENT link fd.

Furthermore, bpf_program__attach_perf_event_opts() is designed for
callers that transfer ownership of the perf_event fd to the returned
bpf_link: when bpf_link__destroy() is called, bpf_link_perf_detach()
unconditionally disables and closes perf_link->perf_event_fd. Because
evsel->core.fd owns FD(evsel, x, y) and closes them in evlist__close(),
destroying the returned bpf_link would double-close the perf_event file
descriptors.

Fix this by attaching the program directly with
ioctl(FD(evsel, x, y), PERF_EVENT_IOC_SET_BPF, fd), matching the pinned
filter path right above it in perf_bpf_filter__prepare(). In the
kernel, PERF_EVENT_IOC_SET_BPF takes a reference on the BPF program and
_free_event() -> perf_event_free_bpf_prog() automatically detaches and
releases it when the perf_event fd is closed. This also avoids enabling
the event prematurely, allowing pe_opts (.dont_enable = true) and the
LIBBPF_CURRENT_VERSION_GEQ(1, 7) guard to be dropped.

Before (built with EXTRA_CFLAGS="-fsanitize=address"):
  # perf record -e cycles --filter 'period > 1000' -- true
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.024 MB perf.data ]

  =================================================================
  ==51328==ERROR: LeakSanitizer: detected memory leaks

  Direct leak of 1568 byte(s) in 28 object(s) allocated from:
      #0 0x7ffbe76ef24f in calloc (/lib64/libasan.so.8+0xef24f)
      #1 0x625df7 in bpf_program__attach_perf_event_opts (tools/perf/perf+0x625df7)
      #2 0xbeddc0 in perf_bpf_filter__prepare util/bpf-filter.c:507
      #3 0x8f3def in evlist__apply_filters util/evlist.c:1421
      #4 0x44bbcf in record__open tools/perf/builtin-record.c:1469
      #5 0x453f9e in __cmd_record tools/perf/builtin-record.c:2594
      #6 0x45dadb in cmd_record tools/perf/builtin-record.c:4427
      #7 0x5df56b in run_builtin tools/perf/perf.c:383
      #8 0x5dfa0e in handle_internal_command tools/perf/perf.c:436
      #9 0x5dfddc in run_argv tools/perf/perf.c:480
      #10 0x5e0333 in main tools/perf/perf.c:581

  SUMMARY: AddressSanitizer: 1568 byte(s) leaked in 28 allocation(s).

After (built with EXTRA_CFLAGS="-fsanitize=address"):
  # perf record -e cycles --filter 'period > 1000' -- true
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.024 MB perf.data ]

Reported-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Closes: https://lore.kernel.org/linux-perf-users/20261020053226.55936-1-namhyung@xxxxxxxxxx/
Fixes: 56ec9457a4a2 ("perf bpf filter: Implement event sample filtering")
Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/util/bpf-filter.c | 17 ++++-------------
 1 file changed, 4 insertions(+), 13 deletions(-)

diff --git a/tools/perf/util/bpf-filter.c b/tools/perf/util/bpf-filter.c
index 72e83ac1d6a4..1596b08fe4e6 100644
--- a/tools/perf/util/bpf-filter.c
+++ b/tools/perf/util/bpf-filter.c
@@ -423,16 +423,8 @@ int perf_bpf_filter__prepare(struct evsel *evsel, struct target *target)
 {
 	int i, x, y, fd, ret;
 	struct sample_filter_bpf *skel = NULL;
-	struct bpf_program *prog;
-	struct bpf_link *link;
 	struct perf_bpf_filter_entry *entry;
 	bool needs_idx_hash = !target__has_cpu(target);
-#if LIBBPF_CURRENT_VERSION_GEQ(1, 7)
-	DECLARE_LIBBPF_OPTS(bpf_perf_event_opts, pe_opts,
-			    .dont_enable = true);
-#else
-	DECLARE_LIBBPF_OPTS(bpf_perf_event_opts, pe_opts);
-#endif
 
 	entry = calloc(MAX_FILTERS, sizeof(*entry));
 	if (entry == NULL)
@@ -501,14 +493,13 @@ int perf_bpf_filter__prepare(struct evsel *evsel, struct target *target)
 		goto err;
 	}
 
-	prog = skel->progs.perf_sample_filter;
+	fd = bpf_program__fd(skel->progs.perf_sample_filter);
 	for (x = 0; x < xyarray__max_x(evsel->core.fd); x++) {
 		for (y = 0; y < xyarray__max_y(evsel->core.fd); y++) {
-			link = bpf_program__attach_perf_event_opts(prog, FD(evsel, x, y),
-								   &pe_opts);
-			if (IS_ERR(link)) {
+			ret = ioctl(FD(evsel, x, y), PERF_EVENT_IOC_SET_BPF, fd);
+			if (ret < 0) {
+				ret = -errno;
 				pr_err("Failed to attach perf sample-filter program\n");
-				ret = PTR_ERR(link);
 				goto err;
 			}
 		}
-- 
2.56.0.212.g129ede20d9-goog