[PATCH] drivers/usb/serial/mos*: prevent reading uninitialized stack memory

[PATCH] drivers/usb/serial/mos*: prevent reading uninitialized stack memory

[Dan Rosenberg]

The TIOCGICOUNT device ioctl in both mos7720.c and mos7840.c allows
unprivileged users to read uninitialized stack memory, because the
"reserved" member of the serial_icounter_struct struct declared on the
stack is not altered or zeroed before being copied back to the user.
This patch takes care of it.

Signed-off-by: Dan Rosenberg <dan.j.rosenberg@gmail.com>

diff -urp linux-2.6.35.4.orig/drivers/usb/serial/mos7720.c linux-2.6.35.4/drivers/usb/serial/mos7720.c
--- linux-2.6.35.4.orig/drivers/usb/serial/mos7720.c	2010-08-26 19:47:12.000000000 -0400
+++ linux-2.6.35.4/drivers/usb/serial/mos7720.c	2010-09-15 11:42:01.877375361 -0400
@@ -2024,6 +2024,9 @@ static int mos7720_ioctl(struct tty_stru
 
 	case TIOCGICOUNT:
 		cnow = mos7720_port->icount;
+
+		memset(&icount, 0, sizeof(struct serial_icounter_struct));
+
 		icount.cts = cnow.cts;
 		icount.dsr = cnow.dsr;
 		icount.rng = cnow.rng;
diff -urp linux-2.6.35.4.orig/drivers/usb/serial/mos7840.c linux-2.6.35.4/drivers/usb/serial/mos7840.c
--- linux-2.6.35.4.orig/drivers/usb/serial/mos7840.c	2010-08-26 19:47:12.000000000 -0400
+++ linux-2.6.35.4/drivers/usb/serial/mos7840.c	2010-09-15 11:42:39.237375173 -0400
@@ -2273,6 +2273,9 @@ static int mos7840_ioctl(struct tty_stru
 	case TIOCGICOUNT:
 		cnow = mos7840_port->icount;
 		smp_rmb();
+
+		memset(&icount, 0, sizeof(struct serial_icounter_struct));
+
 		icount.cts = cnow.cts;
 		icount.dsr = cnow.dsr;
 		icount.rng = cnow.rng;

Re: [PATCH] drivers/usb/serial/mos*: prevent reading uninitialized stack memory

[Alan Cox]

On Wed, 15 Sep 2010 17:44:16 -0400
Dan Rosenberg <drosenberg@vsecurity.com> wrote:

> The TIOCGICOUNT device ioctl in both mos7720.c and mos7840.c allows
> unprivileged users to read uninitialized stack memory, because the
> "reserved" member of the serial_icounter_struct struct declared on the
> stack is not altered or zeroed before being copied back to the user.
> This patch takes care of it.

ACK ... but this is the wrong way to fix these. We'll be squashing new
ones between here and eternity if we just stick memsets in. It wants
making a tty operation off the tty ioctl code so that there is one place
that clears it and copies it to the user.

I'll have a look at what is needed - I don't think very much.

Alan