bpf: Clear user buf when bpf_d_path failed

The bpf_d_path() function may fail. If it does,
clear the user buf, like bpf_probe_read etc.

Signed-off-by: Tao Chen <chen.dylane@linux.dev>
Acked-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20250611154859.259682-1-chen.dylane@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: Tao Chen

kernel/trace/bpf_trace.c

@@ -916,11 +916,14 @@ BPF_CALL_3(bpf_d_path, struct path *, path, char *, buf, u32, sz)
 	 * potentially broken verifier.
 	 */
 	len = copy_from_kernel_nofault(&copy, path, sizeof(*path));
-	if (len < 0)
+	if (len < 0) {
+		memset(buf, 0, sz);
 		return len;
+	}
 
 	p = d_path(&copy, buf, sz);
 	if (IS_ERR(p)) {
+		memset(buf, 0, sz);
 		len = PTR_ERR(p);
 	} else {
 		len = buf + sz - p;