Re: [PATCH bpf v4 1/2] bpf: fix unpopulated name_len field in perf_event link info

On Fri, Oct 4, 2024 at 11:40 PM tyrone-wu wudevelops@gmail.com wrote:

Previously when retrieving `bpf_link_info.perf_event` for kprobe/uprobe/tracepoint, the `name_len` field was not populated by the kernel, leaving it to reflect the value initially set by the user. This behavior was inconsistent with how other input/output string buffer fields function (e.g. `raw_tracepoint.tp_name_len`).

This patch fills `name_len` with the actual size of the string name.

Link: https://lore.kernel.org/bpf/CABVU1kXwQXhqQGe0RTrr7eegtM6SVW_KayZBy16-yb0Snzt... Fixes: 1b715e1b0ec5 ("bpf: Support ->fill_link_info for perf_event") Signed-off-by: tyrone-wu wudevelops@gmail.com Acked-by: Jiri Olsa jolsa@kernel.org

---

V3 -> V4: Link: https://lore.kernel.org/bpf/Zv_PP6Gs5cq3W2Ey@krava/

• Split patch into separate kernel and selftest change

V2 -> V3: Link: https://lore.kernel.org/bpf/Zv7sISV0yEyGlEM3@krava/

• Use clearer variable name for user set/inputted name len (name_len -> input_len)
• Change (name_len -> input_len) type from size_t to u32 since it's only received and used as u32

V1 -> V2: Link: https://lore.kernel.org/bpf/Zv0wl-S13WJnIkb_@krava/

• Use user set *ulen in bpf_copy_to_user before overwriting *ulen

kernel/bpf/syscall.c | 29 ++++++++++++++++++++--------- 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index a8f1808a1ca5..56c556fcf325 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -3565,27 +3565,31 @@ static void bpf_perf_link_dealloc(struct bpf_link *link) }

static int bpf_perf_link_fill_common(const struct perf_event *event,

•                                char __user *uname, u32 ulen,
  

•                                char __user *uname, u32 *ulen,
                                 u64 *probe_offset, u64 *probe_addr,
                                 u32 *fd_type, unsigned long *missed)
  

{ const char *buf;

•   u32 prog_id;
  

•   u32 prog_id, input_len;
    size_t len;
    int err;
  
  

•   if (!ulen ^ !uname)
  

•   if (!(*ulen) ^ !uname)
            return -EINVAL;
  
    err = bpf_get_perf_event_info(event, &prog_id, fd_type, &buf,
                                  probe_offset, probe_addr, missed);
    if (err)
            return err;
  

•   input_len = *ulen;
  

•   len = strlen(buf);
  

The buf might be NULL, so we should check it.

•   *ulen = len + 1;
    if (!uname)
            return 0;
  

•   if (buf) {
  

•           len = strlen(buf);
  

•           err = bpf_copy_to_user(uname, buf, ulen, len);
  

•           err = bpf_copy_to_user(uname, buf, input_len, len);
            if (err)
                    return err;
    } else {
  

@@ -3609,7 +3613,7 @@ static int bpf_perf_link_fill_kprobe(const struct perf_event *event,

    uname = u64_to_user_ptr(info->perf_event.kprobe.func_name);
    ulen = info->perf_event.kprobe.name_len;

•   err = bpf_perf_link_fill_common(event, uname, ulen, &offset, &addr,
  

•   err = bpf_perf_link_fill_common(event, uname, &ulen, &offset, &addr,
                                    &type, &missed);
    if (err)
            return err;
  

@@ -3617,7 +3621,7 @@ static int bpf_perf_link_fill_kprobe(const struct perf_event *event, info->perf_event.type = BPF_PERF_EVENT_KRETPROBE; else info->perf_event.type = BPF_PERF_EVENT_KPROBE;

•   info->perf_event.kprobe.name_len = ulen;
    info->perf_event.kprobe.offset = offset;
    info->perf_event.kprobe.missed = missed;
    if (!kallsyms_show_value(current_cred()))
  

@@ -3639,7 +3643,7 @@ static int bpf_perf_link_fill_uprobe(const struct perf_event *event,

    uname = u64_to_user_ptr(info->perf_event.uprobe.file_name);
    ulen = info->perf_event.uprobe.name_len;

•   err = bpf_perf_link_fill_common(event, uname, ulen, &offset, &addr,
  

•   err = bpf_perf_link_fill_common(event, uname, &ulen, &offset, &addr,
                                    &type, NULL);
    if (err)
            return err;
  

@@ -3648,6 +3652,7 @@ static int bpf_perf_link_fill_uprobe(const struct perf_event *event, info->perf_event.type = BPF_PERF_EVENT_URETPROBE; else info->perf_event.type = BPF_PERF_EVENT_UPROBE;

•   info->perf_event.uprobe.name_len = ulen;
    info->perf_event.uprobe.offset = offset;
    info->perf_event.uprobe.cookie = event->bpf_cookie;
    return 0;
  

@@ -3673,12 +3678,18 @@ static int bpf_perf_link_fill_tracepoint(const struct perf_event *event, { char __user *uname; u32 ulen;

•   int err;
  
    uname = u64_to_user_ptr(info->perf_event.tracepoint.tp_name);
    ulen = info->perf_event.tracepoint.name_len;
  

•   err = bpf_perf_link_fill_common(event, uname, &ulen, NULL, NULL, NULL, NULL);
  

•   if (err)
  

•           return err;
  

•   info->perf_event.type = BPF_PERF_EVENT_TRACEPOINT;
  

•   info->perf_event.tracepoint.name_len = ulen;
    info->perf_event.tracepoint.cookie = event->bpf_cookie;
  

•   return bpf_perf_link_fill_common(event, uname, ulen, NULL, NULL, NULL, NULL);
  

•   return 0;
  

}

static int bpf_perf_link_fill_perf_event(const struct perf_event *event,

2.43.0

-- Regards

Yafang