bpf: don't indicate success when copy_from_user fails

err in bpf_prog_get_info_by_fd() still holds 0 at that time from prior
check_uarg_tail_zero() check. Explicitly return -EFAULT instead, so
user space can be notified of buggy behavior.

Fixes: 1e270976 ("bpf: Add BPF_OBJ_GET_INFO_BY_FD")
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Acked-by: NMartin KaFai Lau <kafai@fb.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

kernel/bpf/syscall.c

@@ -1289,7 +1289,7 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
 	info_len = min_t(u32, sizeof(info), info_len);
 
 	if (copy_from_user(&info, uinfo, info_len))
-		return err;
+		return -EFAULT;
 
 	info.type = prog->type;
 	info.id = prog->aux->id;