bpf: Fix uninitialized symbol in bpf_perf_link_fill_kprobe()

The commit 1b715e1b0ec5 ("bpf: Support ->fill_link_info for perf_event") leads
to the following Smatch static checker warning:

    kernel/bpf/syscall.c:3416 bpf_perf_link_fill_kprobe()
    error: uninitialized symbol 'type'.

That can happens when uname is NULL. So fix it by verifying the uname when we
really need to fill it.

Fixes: 1b715e1b0ec5 ("bpf: Support ->fill_link_info for perf_event")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Closes: https://lore.kernel.org/bpf/85697a7e-f897-4f74-8b43-82721bebc462@kili.mountain
Link: https://lore.kernel.org/bpf/20230813141900.1268-2-laoar.shao@gmail.com

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 7f4e8c3..cb65854 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3378,14 +3378,13 @@ static int bpf_perf_link_fill_common(const struct perf_event *event,
 
        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 (!uname)
+               return 0;
        if (buf) {
                len = strlen(buf);
                err = bpf_copy_to_user(uname, buf, ulen, len);