linux-kernel - [PATCH bpf-next v2] libbpf: Fix event name too long error

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Message-Id: <20250411080545.319865-1-yangfeng59949@163.com>
Date: Fri, 11 Apr 2025 16:05:45 +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 bpf-next v2] 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.

Use basename() to extract the base filename from the full binary path, removing directory prefixes.
Example: /root/loooooooooooooooooooooooooooooooooooong_name -> loooooooooooooooooooooooooooooooooooong_name.

String Length Limitation: Apply %.32s in snprintf to truncate the base filename to 32 characters.
Example: loooooooooooooooooooooooooooooooooooong_name -> looooooooooooooooooooooooooooooo.

Before Fix:
	libbpf: binary_path: /root/loooooooooooooooooooooooooooooooooooong_name
	libbpf: probe_name: libbpf_32296__root_loooooooooooooooooooooooooooooooooooong_name_0x1106
	libbpf: failed to add legacy uprobe event for /root/loooooooooooooooooooooooooooooooooooong_name:0x1106: -22

After Fix:
	libbpf: binary_path: /root/loooooooooooooooooooooooooooooooooooong_name
	libbpf: probe_name: libbpf_36178_looooooooooooooooooooooooooooooo_0x1106

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>
---
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/
---
 tools/lib/bpf/libbpf.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index b2591f5cab65..7e10c7c66819 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_%.32s_0x%zx_%d", getpid(), kfunc_name,
+		 offset, __sync_fetch_and_add(&index, 1));
 
-	/* 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);
@@ -11880,7 +11882,8 @@ static void gen_uprobe_legacy_event_name(char *buf, size_t buf_sz,
 {
 	int i;
 
-	snprintf(buf, buf_sz, "libbpf_%u_%s_0x%zx", getpid(), binary_path, (size_t)offset);
+	snprintf(buf, buf_sz, "libbpf_%u_%.32s_0x%zx", getpid(),
+		 basename((void *)binary_path), (size_t)offset);
 
 	/* sanitize binary_path in the probe name */
 	for (i = 0; buf[i]; i++) {
@@ -12312,7 +12315,7 @@ 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