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Date: Tue, 9 Jun 2015 14:26:39 +0300
From: Solar Designer <solar@...nwall.com>
To: oss-security@...ts.openwall.com
Subject: Re: CVE-2015-1805 Linux kernel: pipe: iovec overrun leading to memory corruption

On Sat, Jun 06, 2015 at 02:30:57PM +0300, Solar Designer wrote:
> The possibility of "struct iovec *iov" going out of range and the
> subsequent out of bounds metadata accesses feel much more severe than
> the out of bounds accesses to actual data in the userspace.
> "iov->iov_base += copy;" and "iov->iov_len -= copy;" might then be
> corrupting kernel memory.  It feels relatively unimportant what the
> resulting values of iov_base and iov_len will be for their intended
> purpose, since we use copy_from_user() / copy_to_user() on them anyway.
> It feels more important that these "+=" and "-=" operators directly
> modify individual words in kernel memory, albeit only slightly(?) out of
> bounds of the original iov array.  So maybe it's this risk that needs
> to be evaluated further.

Upon a closer look, it appears that this is in fact the impact Red Hat
had in mind as well.  I was not reading closely enough.  The "Doc Text"
field at https://bugzilla.redhat.com/show_bug.cgi?id=1202855 says:

"It was found that the Linux kernel's implementation of vectored pipe
read and write functionality did not take into account the I/O vectors
that were already processed when retrying after a failed atomic access
operation, potentially resulting in memory corruption due to an I/O
vector array overrun."

So we're on the same page regarding "I/O vector array overrun" (rather
than I/O data overrun) being the security issue here.

Alexander

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