On Mon, Jul 17, 2023 at 5:14 PM Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
>
> Hello Yafang Shao,
>
> The patch 1b715e1b0ec5: "bpf: Support ->fill_link_info for
> perf_event" from Jul 9, 2023, leads to the following Smatch static
> checker warning:
>
> kernel/bpf/syscall.c:3416 bpf_perf_link_fill_kprobe()
> error: uninitialized symbol 'type'.
Thanks for your report !
>
> kernel/bpf/syscall.c
> 3402 static int bpf_perf_link_fill_kprobe(const struct perf_event *event,
> 3403 struct bpf_link_info *info)
> 3404 {
> 3405 char __user *uname;
> 3406 u64 addr, offset;
> 3407 u32 ulen, type;
> 3408 int err;
> 3409
> 3410 uname = u64_to_user_ptr(info->perf_event.kprobe.func_name);
> 3411 ulen = info->perf_event.kprobe.name_len;
> 3412 err = bpf_perf_link_fill_common(event, uname, ulen, &offset, &addr,
> 3413 &type);
> 3414 if (err)
> 3415 return err;
> --> 3416 if (type == BPF_FD_TYPE_KRETPROBE)
>
> It looks like you could call bpf_get_perf_event_info() without it
> initializing *fd_type to anything.
It can only happen when uname==NULL. So I think the change below can fix it.
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index ee8cb1a..3c29211 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3374,16 +3374,16 @@ static int bpf_perf_link_fill_common(const
struct perf_event *event,
size_t len;
int err;
- if (!ulen ^ !uname)
- return -EINVAL;
- if (!uname)
- return 0;
-
err = bpf_get_perf_event_info(event, &prog_id, fd_type, &buf,
probe_offset, probe_addr);
if (err)
return err;
+ if (!ulen ^ !uname)
+ return -EINVAL;
+ if (!uname)
+ return 0;
+
if (buf) {
len = strlen(buf);
err = bpf_copy_to_user(uname, buf, ulen, len);
> Meanwhile if you initialize it to
> zero here, that won't even affect the compiled code at all because
> everyone zeroes stack data these days.
>
> 3417 info->perf_event.type = BPF_PERF_EVENT_KRETPROBE;
> 3418 else
> 3419 info->perf_event.type = BPF_PERF_EVENT_KPROBE;
> 3420
> 3421 info->perf_event.kprobe.offset = offset;
> 3422 if (!kallsyms_show_value(current_cred()))
> 3423 addr = 0;
> 3424 info->perf_event.kprobe.addr = addr;
> 3425 return 0;
> 3426 }
>
> regards,
> dan carpenter
--
Regards
Yafang
