linux-kernel - [PATCH] waitid(): Avoid unbalanced user_access_end() on access

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Message-ID: <20171020143605.GA59685@beast>
Date:   Fri, 20 Oct 2017 07:36:05 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>, linux-kernel@...r.kernel.org,
        David Daney <ddaney@...iumnetworks.com>
Subject: [PATCH] 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 <viro@...iv.linux.org.uk>
Cc: David Daney <ddaney@...iumnetworks.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
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(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index cf28528842bc..f6cad39f35df 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -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);
-- 
2.7.4


-- 
Kees Cook
Pixel Security