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

Feng Yang
2025-04-14T09:35:41Z

From: Feng Yang <yangfeng@kylinos.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@gmail.com>
Signed-off-by: Feng Yang <yangfeng@kylinos.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