linux-kernel - Re: ima_mmap_file returning 0 to userspace as mmap result.

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Date:	Thu, 5 Jun 2014 12:20:45 -0400
From:	Dave Jones <davej@...hat.com>
To:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Linus Torvalds <torvalds@...ux-foundation.org>,
	zohar@...ux.vnet.ibm.com
Subject: Re: ima_mmap_file returning 0 to userspace as mmap result.

On Thu, Jun 05, 2014 at 11:56:58AM -0400, Dave Jones wrote:
 > On Thu, Jun 05, 2014 at 06:40:36AM +0200, Michael Kerrisk (man-pages) wrote:
 >  > On 06/05/2014 01:31 AM, Dave Jones wrote:
 >  > > I just noticed that trinity was freaking out in places when mmap was
 >  > > returning zero.  This surprised me, because I had the mmap_min_addr
 >  > > sysctl set to 64k, so it wasn't a MAP_FIXED mapping that did it.
 >  > > 
 >  > > There's no mention of this return value in the man page, so I dug
 >  > > into the kernel code, and it appears that we do..
 >  > > 
 >  > > sys_mmap
 >  > > vm_mmap_pgoff
 >  > > security_mmap_file
 >  > > ima_file_mmap <- returns 0 if not PROT_EXEC
 >  > > 
 >  > > and then the 0 gets propagated up as a retval all the way to userspace.
 > 
 > I just realised that this affects even kernels with CONFIG_IMA unset,
 > because there we just do 'return 0' unconditionally.
 > 
 > Also, it appears that kernels with CONFIG_SECURITY unset will also
 > return a zero for the same reason.

Hang on, I was misreading that whole security_mmap_file ret handling code.
There's something else at work here.  I'll dig and get a reproducer.

	Dave

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