From: Al Viro <viro@ftp.linux.org.uk>
To: sk b <skb300@hotmail.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: user pointers and race conditions
Date: Thu, 17 May 2007 06:04:36 +0100 [thread overview]
Message-ID: <20070517050436.GN4095@ftp.linux.org.uk> (raw)
In-Reply-To: <BAY115-W33D3EC723171255D88FBF86330@phx.gbl>
On Wed, May 16, 2007 at 10:56:22PM -0600, sk b wrote:
>
> Hello,
>
> I'm wondering whether there is an exploitable TOCTTOU race condition in the way user pointers are handled in the kernel. Consider the following code:
>
> 1: struct st { int *u; };
> 2: void syscall(struct st * stp) {
> 3: if (!access_ok(VERIFY_READ,stp,sizeof(struct st)))
> 4: return;
> 5: if (!access_ok(VERIFY_WRITE,stp->u,sizeof(int)))
... and there's your bug - direct access to userland data. The normal
variant is to use accessors (get_user() or copy_from_user()) to fetch
the value of stp->u. At which point races of the kind you mentioned
take an obviously dumb code (explicitly copying the same struct from
userland _twice_).
next prev parent reply other threads:[~2007-05-17 5:04 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-05-17 4:56 sk b
2007-05-17 5:04 ` Al Viro [this message]
2007-05-17 5:06 ` David Miller
2007-05-17 12:26 ` Arjan van de Ven
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