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From:   Eric Biggers <ebiggers@kernel.org>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>
Cc:     linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
        Al Viro <viro@zeniv.linux.org.uk>
Subject: [PATCH v2 1/2] tty: fix compat TIOCGSERIAL leaking uninitialized memory
Date:   Mon, 24 Feb 2020 10:20:43 -0800
Message-Id: <20200224182044.234553-2-ebiggers@kernel.org>
In-Reply-To: <20200224182044.234553-1-ebiggers@kernel.org>
References: <20200224181532.GA109047@gmail.com>
 <20200224182044.234553-1-ebiggers@kernel.org>
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From: Eric Biggers <ebiggers@google.com>

Commit 77654350306a ("take compat TIOC[SG]SERIAL treatment into
tty_compat_ioctl()") changed the compat version of TIOCGSERIAL to start
copying a whole 'serial_struct32' to userspace rather than individual
fields, but failed to initialize all padding and fields -- namely the
hole after the 'iomem_reg_shift' field, and the 'reserved' field.

Fix this by initializing the struct to zero.

[v2: use sizeof, and convert the adjacent line for consistency.]

Reported-by: syzbot+8da9175e28eadcb203ce@syzkaller.appspotmail.com
Fixes: 77654350306a ("take compat TIOC[SG]SERIAL treatment into tty_compat_ioctl()")
Cc: <stable@vger.kernel.org> # v4.20+
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 drivers/tty/tty_io.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 1fcf7ad83dfa0a..db4a13bc855ed6 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2730,7 +2730,9 @@ static int compat_tty_tiocgserial(struct tty_struct *tty,
 	struct serial_struct32 v32;
 	struct serial_struct v;
 	int err;
-	memset(&v, 0, sizeof(struct serial_struct));
+
+	memset(&v, 0, sizeof(v));
+	memset(&v32, 0, sizeof(v32));
 
 	if (!tty->ops->set_serial)
 		return -ENOTTY;
-- 
2.25.0.265.gbab2e86ba0-goog