[PATCH 4.13 2/2] waitid(): Add missing access_ok() checks

[Greg Kroah-Hartman]

4.13-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kees Cook <keesc...@chromium.org>

commit 96ca579a1ecc943b75beba58bebb0356f6cc4b51 upstream.

Adds missing access_ok() checks.

CVE-2017-5123

Reported-by: Chris Salls <chrissal...@gmail.com>
Signed-off-by: Kees Cook <keesc...@chromium.org>
Acked-by: Al Viro <v...@zeniv.linux.org.uk>
Fixes: 4c48abe91be0 ("waitid(): switch copyout of siginfo to unsafe_put_user()")
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 kernel/exit.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1611,6 +1611,9 @@ SYSCALL_DEFINE5(waitid, int, which, pid_
        if (!infop)
                return err;
 
+       if (!access_ok(VERIFY_WRITE, infop, sizeof(*infop)))
+               goto Efault;
+
        user_access_begin();
        unsafe_put_user(signo, &infop->si_signo, Efault);
        unsafe_put_user(0, &infop->si_errno, Efault);
@@ -1736,6 +1739,9 @@ COMPAT_SYSCALL_DEFINE5(waitid,
        if (!infop)
                return err;
 
+       if (!access_ok(VERIFY_WRITE, infop, sizeof(*infop)))
+               goto Efault;
+
        user_access_begin();
        unsafe_put_user(signo, &infop->si_signo, Efault);
        unsafe_put_user(0, &infop->si_errno, Efault);