linux-kernel - [PATCH v3 bpf-next 1/3] libbpf: Fix event name too long error

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Message-Id: <20250414093402.384872-2-yangfeng59949@163.com>
Date: Mon, 14 Apr 2025 17:34:00 +0800
From: Feng Yang <yangfeng59949@....com>
To: ast@...nel.org,
	daniel@...earbox.net,
	andrii@...nel.org,
	martin.lau@...ux.dev,
	eddyz87@...il.com,
	song@...nel.org,
	yonghong.song@...ux.dev,
	john.fastabend@...il.com,
	kpsingh@...nel.org,
	sdf@...ichev.me,
	haoluo@...gle.com,
	jolsa@...nel.org,
	hengqi.chen@...il.com
Cc: bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v3 bpf-next 1/3] libbpf: Fix event name too long error

From: Feng Yang <yangfeng@...inos.cn>

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.

Before Fix:
	./test_progs -t attach_probe/kprobe-long_name
	......
	libbpf: failed to add legacy kprobe event for 'bpf_kfunc_looooooooooooooooooooooooooooooong_name+0x0': -EINVAL
	libbpf: prog 'handle_kprobe': failed to create kprobe 'bpf_kfunc_looooooooooooooooooooooooooooooong_name+0x0' perf event: -EINVAL
	test_attach_kprobe_long_event_name:FAIL:attach_kprobe_long_event_name unexpected error: -22
	test_attach_probe:PASS:uprobe_ref_ctr_cleanup 0 nsec
	#13/11   attach_probe/kprobe-long_name:FAIL
	#13      attach_probe:FAIL

	./test_progs -t attach_probe/uprobe-long_name
	......
	libbpf: failed to add legacy uprobe event for /root/linux-bpf/bpf-next/tools/testing/selftests/bpf/test_progs:0x13efd9: -EINVAL
	libbpf: prog 'handle_uprobe': failed to create uprobe '/root/linux-bpf/bpf-next/tools/testing/selftests/bpf/test_progs:0x13efd9' perf event: -EINVAL
	test_attach_uprobe_long_event_name:FAIL:attach_uprobe_long_event_name unexpected error: -22
	#13/10   attach_probe/uprobe-long_name:FAIL
	#13      attach_probe:FAIL
After Fix:
	./test_progs -t attach_probe/uprobe-long_name
	#13/10   attach_probe/uprobe-long_name:OK
	#13      attach_probe:OK
	Summary: 1/1 PASSED, 0 SKIPPED, 0 FAILED

	./test_progs -t attach_probe/kprobe-long_name
	#13/11   attach_probe/kprobe-long_name:OK
	#13      attach_probe:OK
	Summary: 1/1 PASSED, 0 SKIPPED, 0 FAILED

Fixes: 46ed5fc33db9 ("libbpf: Refactor and simplify legacy kprobe code")
Fixes: cc10623c6810 ("libbpf: Add legacy uprobe attaching support")
Signed-off-by: Hengqi Chen <hengqi.chen@...il.com>
Signed-off-by: Feng Yang <yangfeng@...inos.cn>
---
 tools/lib/bpf/libbpf.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b2591f5cab65..9e047641e001 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))
@@ -11142,10 +11144,10 @@ static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz,
 	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), kfunc_name, offset);
 
-	/* sanitize binary_path in the probe name */
+	/* sanitize kfunc_name in the probe name */
 	for (i = 0; buf[i]; i++) {
 		if (!isalnum(buf[i]))
 			buf[i] = '_';
@@ -11270,7 +11272,7 @@ 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);
 		if (add_kprobe_event_legacy(probe_name, false, syscall_name, 0) < 0)
@@ -11328,7 +11330,7 @@ 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);
@@ -11878,9 +11880,12 @@ static int attach_uprobe_multi(const struct bpf_program *prog, long cookie, stru
 static void gen_uprobe_legacy_event_name(char *buf, size_t buf_sz,
 					 const char *binary_path, uint64_t offset)
 {
+	static int index = 0;
 	int i;
 
-	snprintf(buf, buf_sz, "libbpf_%u_%s_0x%zx", getpid(), binary_path, (size_t)offset);
+	snprintf(buf, buf_sz, "libbpf_%u_%d_%s_0x%zx", getpid(),
+		 __sync_fetch_and_add(&index, 1),
+		 basename((void *)binary_path), (size_t)offset);
 
 	/* sanitize binary_path in the probe name */
 	for (i = 0; buf[i]; i++) {
@@ -12312,7 +12317,7 @@ 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);
-- 
2.43.0