Merge branch 'libbpf-fix-event-name-too-long-error-and-add-tests'

Feng Yang says:

====================
libbpf: Fix event name too long error and add tests

From: Feng Yang <yangfeng@kylinos.cn>

Hi everyone,

This series tries to fix event name too long error and add tests.

When the binary path is excessively long, the generated probe_name in libbpf
exceeds the kernel's MAX_EVENT_NAME_LEN limit (64 bytes).
This causes legacy uprobe event attachment to fail with error code -22.

The fix reorders the fields to place the unique ID before the name.
This ensures that even if truncation occurs via snprintf, the unique ID
remains intact, preserving event name uniqueness. Additionally, explicit
checks with MAX_EVENT_NAME_LEN are added to enforce length constraints.
Acked-by: Jiri Olsa <jolsa@kernel.org>
---
Changes in v5:
- use strrchr instead of basename.
- kprobe_test add __weak. Thanks, Andrii Nakryiko!
- Link to v4: https://lore.kernel.org/all/20250415093907.280501-1-yangfeng59949@163.com/

Changes in v4:
- add changelog.
- gen_uprobe_legacy_event_name and gen_kprobe_legacy_event_name are combined into a function
- kprobe_test use normal module function. Thanks, Jiri Olsa!
- Link to v3: https://lore.kernel.org/bpf/20250414093402.384872-1-yangfeng59949@163.com/

Changes in v3:
- add __sync_fetch_and_add(&index) and let snprintf() do the trimming. Thanks, Andrii Nakryiko!
- add selftests.
- Link to v2: https://lore.kernel.org/all/20250411080545.319865-1-yangfeng59949@163.com/

Changes in v2:
- Use basename() and %.32s to fix. Thanks, Hengqi Chen!
- Link to v1: https://lore.kernel.org/all/20250410052712.206785-1-yangfeng59949@163.com/
====================

Link: https://patch.msgid.link/20250417014848.59321-1-yangfeng59949@163.com
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

3 files changed, 104 insertions, 27 deletions

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 56250b5ac5b0..fbb991c6bf19 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -60,6 +60,8 @@
 #define BPF_FS_MAGIC		0xcafe4a11
 #endif
 
+#define MAX_EVENT_NAME_LEN	64
+
 #define BPF_FS_DEFAULT_PATH "/sys/fs/bpf"
 
 #define BPF_INSN_SZ (sizeof(struct bpf_insn))
@@ -11136,16 +11138,16 @@ static const char *tracefs_available_filter_functions_addrs(void)
 			     : TRACEFS"/available_filter_functions_addrs";
 }
 
-static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz,
-					 const char *kfunc_name, size_t offset)
+static void gen_probe_legacy_event_name(char *buf, size_t buf_sz,
+					const char *name, size_t offset)
 {
 	static int index = 0;
 	int i;
 
-	snprintf(buf, buf_sz, "libbpf_%u_%s_0x%zx_%d", getpid(), kfunc_name, offset,
-		 __sync_fetch_and_add(&index, 1));
+	snprintf(buf, buf_sz, "libbpf_%u_%d_%s_0x%zx", getpid(),
+		 __sync_fetch_and_add(&index, 1), name, offset);
 
-	/* sanitize binary_path in the probe name */
+	/* sanitize name in the probe name */
 	for (i = 0; buf[i]; i++) {
 		if (!isalnum(buf[i]))
 			buf[i] = '_';
@@ -11270,9 +11272,9 @@ int probe_kern_syscall_wrapper(int token_fd)
 
 		return pfd >= 0 ? 1 : 0;
 	} else { /* legacy mode */
-		char probe_name[128];
+		char probe_name[MAX_EVENT_NAME_LEN];
 
-		gen_kprobe_legacy_event_name(probe_name, sizeof(probe_name), syscall_name, 0);
+		gen_probe_legacy_event_name(probe_name, sizeof(probe_name), syscall_name, 0);
 		if (add_kprobe_event_legacy(probe_name, false, syscall_name, 0) < 0)
 			return 0;
 
@@ -11328,10 +11330,10 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
 					    func_name, offset,
 					    -1 /* pid */, 0 /* ref_ctr_off */);
 	} else {
-		char probe_name[256];
+		char probe_name[MAX_EVENT_NAME_LEN];
 
-		gen_kprobe_legacy_event_name(probe_name, sizeof(probe_name),
-					     func_name, offset);
+		gen_probe_legacy_event_name(probe_name, sizeof(probe_name),
+					    func_name, offset);
 
 		legacy_probe = strdup(probe_name);
 		if (!legacy_probe)
@@ -11875,20 +11877,6 @@ static int attach_uprobe_multi(const struct bpf_program *prog, long cookie, stru
 	return ret;
 }
 
-static void gen_uprobe_legacy_event_name(char *buf, size_t buf_sz,
-					 const char *binary_path, uint64_t offset)
-{
-	int i;
-
-	snprintf(buf, buf_sz, "libbpf_%u_%s_0x%zx", getpid(), binary_path, (size_t)offset);
-
-	/* sanitize binary_path in the probe name */
-	for (i = 0; buf[i]; i++) {
-		if (!isalnum(buf[i]))
-			buf[i] = '_';
-	}
-}
-
 static inline int add_uprobe_event_legacy(const char *probe_name, bool retprobe,
 					  const char *binary_path, size_t offset)
 {
@@ -12312,13 +12300,14 @@ bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid,
 		pfd = perf_event_open_probe(true /* uprobe */, retprobe, binary_path,
 					    func_offset, pid, ref_ctr_off);
 	} else {
-		char probe_name[PATH_MAX + 64];
+		char probe_name[MAX_EVENT_NAME_LEN];
 
 		if (ref_ctr_off)
 			return libbpf_err_ptr(-EINVAL);
 
-		gen_uprobe_legacy_event_name(probe_name, sizeof(probe_name),
-					     binary_path, func_offset);
+		gen_probe_legacy_event_name(probe_name, sizeof(probe_name),
+					    strrchr(binary_path, '/') ? : binary_path,
+					    func_offset);
 
 		legacy_probe = strdup(probe_name);
 		if (!legacy_probe)
diff --git a/tools/testing/selftests/bpf/prog_tests/attach_probe.c b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
index 329c7862b52d..cabc51c2ca6b 100644
--- a/tools/testing/selftests/bpf/prog_tests/attach_probe.c
+++ b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
@@ -122,6 +122,85 @@ cleanup:
 	test_attach_probe_manual__destroy(skel);
 }
 
+/* attach uprobe/uretprobe long event name testings */
+static void test_attach_uprobe_long_event_name(void)
+{
+	DECLARE_LIBBPF_OPTS(bpf_uprobe_opts, uprobe_opts);
+	struct bpf_link *uprobe_link, *uretprobe_link;
+	struct test_attach_probe_manual *skel;
+	ssize_t uprobe_offset;
+	char path[PATH_MAX] = {0};
+
+	skel = test_attach_probe_manual__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_kprobe_manual_open_and_load"))
+		return;
+
+	uprobe_offset = get_uprobe_offset(&trigger_func);
+	if (!ASSERT_GE(uprobe_offset, 0, "uprobe_offset"))
+		goto cleanup;
+
+	if (!ASSERT_GT(readlink("/proc/self/exe", path, PATH_MAX - 1), 0, "readlink"))
+		goto cleanup;
+
+	/* manual-attach uprobe/uretprobe */
+	uprobe_opts.attach_mode = PROBE_ATTACH_MODE_LEGACY;
+	uprobe_opts.ref_ctr_offset = 0;
+	uprobe_opts.retprobe = false;
+	uprobe_link = bpf_program__attach_uprobe_opts(skel->progs.handle_uprobe,
+						      0 /* self pid */,
+						      path,
+						      uprobe_offset,
+						      &uprobe_opts);
+	if (!ASSERT_OK_PTR(uprobe_link, "attach_uprobe_long_event_name"))
+		goto cleanup;
+	skel->links.handle_uprobe = uprobe_link;
+
+	uprobe_opts.retprobe = true;
+	uretprobe_link = bpf_program__attach_uprobe_opts(skel->progs.handle_uretprobe,
+							 -1 /* any pid */,
+							 path,
+							 uprobe_offset, &uprobe_opts);
+	if (!ASSERT_OK_PTR(uretprobe_link, "attach_uretprobe_long_event_name"))
+		goto cleanup;
+	skel->links.handle_uretprobe = uretprobe_link;
+
+cleanup:
+	test_attach_probe_manual__destroy(skel);
+}
+
+/* attach kprobe/kretprobe long event name testings */
+static void test_attach_kprobe_long_event_name(void)
+{
+	DECLARE_LIBBPF_OPTS(bpf_kprobe_opts, kprobe_opts);
+	struct bpf_link *kprobe_link, *kretprobe_link;
+	struct test_attach_probe_manual *skel;
+
+	skel = test_attach_probe_manual__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_kprobe_manual_open_and_load"))
+		return;
+
+	/* manual-attach kprobe/kretprobe */
+	kprobe_opts.attach_mode = PROBE_ATTACH_MODE_LEGACY;
+	kprobe_opts.retprobe = false;
+	kprobe_link = bpf_program__attach_kprobe_opts(skel->progs.handle_kprobe,
+						      "bpf_testmod_looooooooooooooooooooooooooooooong_name",
+						      &kprobe_opts);
+	if (!ASSERT_OK_PTR(kprobe_link, "attach_kprobe_long_event_name"))
+		goto cleanup;
+	skel->links.handle_kprobe = kprobe_link;
+
+	kprobe_opts.retprobe = true;
+	kretprobe_link = bpf_program__attach_kprobe_opts(skel->progs.handle_kretprobe,
+							 "bpf_testmod_looooooooooooooooooooooooooooooong_name",
+							 &kprobe_opts);
+	if (!ASSERT_OK_PTR(kretprobe_link, "attach_kretprobe_long_event_name"))
+		goto cleanup;
+	skel->links.handle_kretprobe = kretprobe_link;
+
+cleanup:
+	test_attach_probe_manual__destroy(skel);
+}
+
 static void test_attach_probe_auto(struct test_attach_probe *skel)
 {
 	struct bpf_link *uprobe_err_link;
@@ -323,6 +402,11 @@ void test_attach_probe(void)
 	if (test__start_subtest("uprobe-ref_ctr"))
 		test_uprobe_ref_ctr(skel);
 
+	if (test__start_subtest("uprobe-long_name"))
+		test_attach_uprobe_long_event_name();
+	if (test__start_subtest("kprobe-long_name"))
+		test_attach_kprobe_long_event_name();
+
 cleanup:
 	test_attach_probe__destroy(skel);
 	ASSERT_EQ(uprobe_ref_ctr, 0, "uprobe_ref_ctr_cleanup");
diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
index f38eaf0d35ef..2e54b95ad898 100644
--- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
@@ -134,6 +134,10 @@ bpf_testmod_test_arg_ptr_to_struct(struct bpf_testmod_struct_arg_1 *a) {
 	return bpf_testmod_test_struct_arg_result;
 }
 
+__weak noinline void bpf_testmod_looooooooooooooooooooooooooooooong_name(void)
+{
+}
+
 __bpf_kfunc void
 bpf_testmod_test_mod_kfunc(int i)
 {