netdev - Re: [PATCH] isdnloop: NUL-terminate strings from userspace

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20140401103020.GG24150@order.stressinduktion.org>
Date:	Tue, 1 Apr 2014 12:30:20 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Vegard Nossum <vegard.nossum@...cle.com>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Dan Carpenter <dan.carpenter@...cle.com>,
	"David S. Miller" <davem@...emloft.net>, stable@...r.kernel.org
Subject: Re: [PATCH] isdnloop: NUL-terminate strings from userspace

On Tue, Apr 01, 2014 at 12:08:18PM +0200, Vegard Nossum wrote:
> Both the in-kernel and BSD strlcpy() require that the source string is
> NUL terminated. We could use strncpy() + explicitly terminate the result,
> but this relies on src and dest having the same size, so the safest thing
> to do seems to explicitly terminate the source string before doing the
> strlcpy().
> 
> Fixes: f9a23c84486ed35 ("isdnloop: use strlcpy() instead of strcpy()")
> Cc: Dan Carpenter <dan.carpenter@...cle.com>
> Cc: David S. Miller <davem@...emloft.net>
> Cc: stable@...r.kernel.org
> Signed-off-by: Vegard Nossum <vegard.nossum@...cle.com>
> ---
>  drivers/isdn/isdnloop/isdnloop.c |    8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/isdn/isdnloop/isdnloop.c b/drivers/isdn/isdnloop/isdnloop.c
> index 02125e6..50cd348 100644
> --- a/drivers/isdn/isdnloop/isdnloop.c
> +++ b/drivers/isdn/isdnloop/isdnloop.c
> @@ -1070,6 +1070,14 @@ isdnloop_start(isdnloop_card *card, isdnloop_sdef *sdefp)
>  		return -EBUSY;
>  	if (copy_from_user((char *) &sdef, (char *) sdefp, sizeof(sdef)))
>  		return -EFAULT;
> +
> +	/*
> +	 * Null terminate strings from userspace so we don't have to worry
> +	 * about this later on.
> +	 */
> +	for (i = 0; i < 3; i++)
> +		sdef.num[i][sizeof(sdef.num[0]) - 1] = '\0';
> +

Looking down the problem, it seems the problem is that the strlen in strlcpy
could read beyond the input buffer?

To prevent this problem in other parts of the kernel wouldn't it be better to
replace the strlen with strnlen in strlcpy?

Bye,

  Hannes

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html