linux-kernel - [PATCH 4.14 22/62] compat: fix 4-byte infoleak via uninitialized struct field

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Date:   Mon, 14 May 2018 08:48:38 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.14 22/62] compat: fix 4-byte infoleak via uninitialized struct field

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

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

From: Jann Horn <jannh@...gle.com>

commit 0a0b98734479aa5b3c671d5190e86273372cab95 upstream.

Commit 3a4d44b61625 ("ntp: Move adjtimex related compat syscalls to
native counterparts") removed the memset() in compat_get_timex().  Since
then, the compat adjtimex syscall can invoke do_adjtimex() with an
uninitialized ->tai.

If do_adjtimex() doesn't write to ->tai (e.g.  because the arguments are
invalid), compat_put_timex() then copies the uninitialized ->tai field
to userspace.

Fix it by adding the memset() back.

Fixes: 3a4d44b61625 ("ntp: Move adjtimex related compat syscalls to native counterparts")
Signed-off-by: Jann Horn <jannh@...gle.com>
Acked-by: Kees Cook <keescook@...omium.org>
Acked-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/compat.c |    1 +
 1 file changed, 1 insertion(+)

--- a/kernel/compat.c
+++ b/kernel/compat.c
@@ -34,6 +34,7 @@ int compat_get_timex(struct timex *txc,
 {
 	struct compat_timex tx32;
 
+	memset(txc, 0, sizeof(struct timex));
 	if (copy_from_user(&tx32, utp, sizeof(struct compat_timex)))
 		return -EFAULT;