libbpf: Cleanup the legacy kprobe_event on failed add/attach_event()

Before the 0bc11ed5ab60 commit ("kprobes: Allow kprobes coexist with
livepatch"), in a scenario where livepatch and kprobe coexist on the
same function entry, the creation of kprobe_event using
add_kprobe_event_legacy() will be successful, at the same time as a
trace event (e.g. /debugfs/tracing/events/kprobe/XXX) will exist, but
perf_event_open() will return an error because both livepatch and kprobe
use FTRACE_OPS_FL_IPMODIFY. As follows:

1) add a livepatch

$ insmod livepatch-XXX.ko

2) add a kprobe using tracefs API (i.e. add_kprobe_event_legacy)

$ echo 'p:mykprobe XXX' > /sys/kernel/debug/tracing/kprobe_events

3) enable this kprobe (i.e. sys_perf_event_open)

This will return an error, -EBUSY.

On Andrii Nakryiko's comment, few error paths in
bpf_program__attach_kprobe_opts() that should need to call
remove_kprobe_event_legacy().

With this patch, whenever an error is returned after
add_kprobe_event_legacy() or bpf_program__attach_perf_event_opts(), this
ensures that the created kprobe_event is cleaned.

Signed-off-by: Chuang Wang <nashuiliang@gmail.com>
Signed-off-by: Jingren Zhou <zhoujingren@didiglobal.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220629151848.65587-2-nashuiliang@gmail.com

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 64c4cc6..8a441d3 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9877,10 +9877,11 @@ static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe,
        }
        type = determine_kprobe_perf_type_legacy(probe_name, retprobe);
        if (type < 0) {
+               err = type;
                pr_warn("failed to determine legacy kprobe event id for '%s+0x%zx': %s\n",
                        kfunc_name, offset,
-                       libbpf_strerror_r(type, errmsg, sizeof(errmsg)));
-               return type;
+                       libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
+               goto err_clean_legacy;
        }
        attr.size = sizeof(attr);
        attr.config = type;
@@ -9894,9 +9895,14 @@ static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe,
                err = -errno;
                pr_warn("legacy kprobe perf_event_open() failed: %s\n",
                        libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
-               return err;
+               goto err_clean_legacy;
        }
        return pfd;
+
+err_clean_legacy:
+       /* Clear the newly added legacy kprobe_event */
+       remove_kprobe_event_legacy(probe_name, retprobe);
+       return err;
 }
 
 struct bpf_link *
@@ -9953,7 +9959,7 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
                        prog->name, retprobe ? "kretprobe" : "kprobe",
                        func_name, offset,
                        libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
-               goto err_out;
+               goto err_clean_legacy;
        }
        if (legacy) {
                struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link);
@@ -9964,6 +9970,10 @@ bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
        }
 
        return link;
+
+err_clean_legacy:
+       if (legacy)
+               remove_kprobe_event_legacy(legacy_probe, retprobe);
 err_out:
        free(legacy_probe);
        return libbpf_err_ptr(err);