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Date: Mon, 24 Oct 2011 10:02:46 +0530
From: Huzaifa Sidhpurwala <huzaifas@...hat.com>
To: oss-security@...ts.openwall.com, Solar Designer <solar@...nwall.com>
Subject: Re: hardlink(1) has buffer overflows, is unsafe on
changing trees
On 10/22/2011 08:51 AM, Solar Designer wrote:
>
> I investigated the non-crashing build further. No, adding more
> directories did not cause a crash either. What happens is that lstat()
> starts failing with ENAMETOOLONG shortly _after_ the overflow occurs.
> This happens to limit the largest overflow size. If "dirs" is not yet
> overwritten by this point (was not reached by the overflow), then the
> program may proceed without crashing and without descending to deeper
> directories (thus not overflowing the buffer even further). So
> different builds may be affected to a different extent, depending on
> relative placement of variables in .bss. The behavior may also vary by
> kernel version, though (when lstat() starts to fail is a property of the
> kernel, whereas NAMELEN in hardlink.c is fixed). I am able to make this
> build crash with "*** buffer overflow detected ***" on the strcat(),
> though, by carefully adjusting the directory name lengths (but that's
> relatively uninteresting).
>
I think this is exactly what i hit, when testing on some Fedora/RHEL
machines.
Kernel defines the following:
#define PATH_MAX 4096 /* # chars in a path name including nul */
And in the lstat implementation:
if (dentry->d_name.len > NAME_MAX)
return ERR_PTR(-ENAMETOOLONG);
--
Huzaifa Sidhpurwala / Red Hat Security Response Team
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