compat: fix 4-byte infoleak via uninitialized struct field

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@google.com>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/compat.c b/kernel/compat.c
index 772e038d04d9a85ef6e78c2df8924ca5348fce78..7e83733d4c95c854c1a4acf2b8b7a96bf91c0d59 100644 (file)
--- a/kernel/compat.c
+++ b/kernel/compat.c
@@ -34,6 +34,7 @@ int compat_get_timex(struct timex *txc, const struct compat_timex __user *utp)
 {
        struct compat_timex tx32;
 
+       memset(txc, 0, sizeof(struct timex));
        if (copy_from_user(&tx32, utp, sizeof(struct compat_timex)))
                return -EFAULT;