[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAEAjamvv7LzaTBu-Xh5rg4r1-_NaDDGVoe9LZ7NmZv3gpLXkuw@mail.gmail.com>
Date: Mon, 23 Mar 2020 16:44:31 -0400
From: Kyungtae Kim <kt0755@...il.com>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: jslaby@...e.com, slyfox@...too.org,
Dmitry Torokhov <dmitry.torokhov@...il.com>, rei4dan@...il.com,
Dave Tian <dave.jing.tian@...il.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: UBSAN: Undefined behaviour in drivers/tty/vt/keyboard.c
On Mon, Mar 23, 2020 at 07:46:16AM +0100, Greg KH wrote:
> On Sun, Mar 22, 2020 at 11:34:01PM -0400, Kyungtae Kim wrote:
> > We report a bug (in linux-5.5.11) found by FuzzUSB (modified version
> > of syzkaller)
> >
> > Seems the variable "npadch" has a very large value (i.e., 333333333)
> > as a result of multiple executions of the function "k_ascii" (keyboard.c:888)
> > while the variable "base" has 10.
> > So their multiplication at line 888 in "k_ascii" will become
> > larger than the max of type int, causing such an integer overflow.
> >
> > I believe this can be solved by checking for overflow ahead of operations
> > e.g., using check_mul_overflow().
> >
> > kernel config: https://kt0755.github.io/etc/config_v5.5.11
>
> Great, can you send a patch for this?
>
> thanks,
>
> greg k-h
I'm not sure the following works best.
diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
index 15d33fa0c925..c1ae9d2e6970 100644
--- a/drivers/tty/vt/keyboard.c
+++ b/drivers/tty/vt/keyboard.c
@@ -869,6 +869,7 @@ static void k_meta(struct vc_data *vc, unsigned
char value, char up_flag)
static void k_ascii(struct vc_data *vc, unsigned char value, char up_flag)
{
int base;
+ int bytes, res;
if (up_flag)
return;
@@ -884,6 +885,8 @@ static void k_ascii(struct vc_data *vc, unsigned
char value, char up_flag)
if (npadch == -1)
npadch = value;
+ else if (check_mul_overflow(npadch, base, &bytes) ||
check_add_overflow(bytes, value, &res))
+ return;
else
npadch = npadch * base + value;
}
Thanks,
Kyungtae Kim
Powered by blists - more mailing lists