linux-kernel - Re: [PATCH v2 4/7] fs/proc/task_mmu.c: shift mm_access() from m_start() to proc_maps

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: <20140806100506.GD30508@node.dhcp.inet.fi>
Date:	Wed, 6 Aug 2014 13:05:06 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	David Howells <dhowells@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Sasha Levin <levinsasha928@...il.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/7] fs/proc/task_mmu.c: shift mm_access() from
 m_start() to proc_maps_open()

On Tue, Aug 05, 2014 at 09:46:55PM +0200, Oleg Nesterov wrote:
> A simple test-case from Kirill Shutemov
> 
> 	cat /proc/self/maps >/dev/null
> 	chmod +x /proc/self/net/packet
> 	exec /proc/self/net/packet
> 
> makes lockdep unhappy, cat/exec take seq_file->lock + cred_guard_mutex in
> the opposite order.
> 
> It's a false positive and probably we should not allow "chmod +x" on proc
> files. Still I think that we should avoid mm_access() and cred_guard_mutex
> in sys_read() paths, security checking should happen at open time. Besides,
> this doesn't even look right if the task changes its ->mm between m_stop()
> and m_start().
> 
> Add the new "mm_struct *mm" member into struct proc_maps_private and change
> proc_maps_open() to initialize it using proc_mem_open(). Change m_start() to
> use priv->mm if atomic_inc_not_zero(mm_users) succeeds or return NULL (eof)
> otherwise.
> 
> The only complication is that proc_maps_open() users should additionally do
> mmdrop() in fop->release(), add the new proc_map_release() helper for that.
> 
> Note: this is the user-visible change, if the task execs after open("maps")
> the new ->mm won't be visible via this file. I hope this is fine, and this
> matches /proc/pid/mem bahaviour.
> 
> Reported-by: "Kirill A. Shutemov" <kirill@...temov.name>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
-- 
 Kirill A. Shutemov
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/