waitid(): Avoid unbalanced user_access_end() on access_ok() error

As pointed out by Linus and David, the earlier waitid() fix resulted in a (currently harmless) unbalanced user_access_end() call. This fixes it to just directly return EFAULT on access_ok() failure.

Fixes 96ca579a1ecc ("waitid(): Add missing access_ok() checks")

Cc Al Viro <[email protected]>

Cc David Daney <[email protected]>

Signed-off-by Kees Cook <[email protected]>

---
This seems best to get fixed up now (in the same release where it was introduced) before it tries to bite us at some later time.

---
  kernel/exit.c | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

kernel/exit.c +2 -2

index cf28528842bc..f6cad39f35df 100644
@@ -1611,7 +1611,7 @@ SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
  		return err;
 
  	if (!access_ok(VERIFY_WRITE, infop, sizeof(*infop)))
-		goto Efault;
+		return -EFAULT;
 
  	user_access_begin();
  	unsafe_put_user(signo, &infop->si_signo, Efault);

@@ -1739,7 +1739,7 @@ COMPAT_SYSCALL_DEFINE5(waitid,
  		return err;
 
  	if (!access_ok(VERIFY_WRITE, infop, sizeof(*infop)))
-		goto Efault;
+		return -EFAULT;
 
  	user_access_begin();
  	unsafe_put_user(signo, &infop->si_signo, Efault);