linux-kernel - Re: UBSAN: Undefined behaviour in drivers/tty/vt/keyboard.c

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Message-ID: <20200323064616.GB129571@kroah.com>
Date:   Mon, 23 Mar 2020 07:46:16 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Kyungtae Kim <kt0755@...il.com>
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 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