linux-kernel - Re: [PATCH, RESEND] procfs: silence lockdep warning about read vs. exec seq

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Date:	Mon, 04 Aug 2014 20:42:11 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Howells <dhowells@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Sasha Levin <levinsasha928@...il.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH, RESEND] procfs: silence lockdep warning about read vs. exec seq_file

"Kirill A. Shutemov" <kirill@...temov.name> writes:

> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
>
> Testcase:
>
>   cat /proc/self/maps >/dev/null
>   chmod +x /proc/self/net/packet
>   exec /proc/self/net/packet
>
> It triggers lockdep warning:

> I don't know why we allow "chmod +x" on some proc files, notably net-related.
> Is it a bug?

It looks like we simply did not remove the ability to make those files
executable when we realized executable proc files could be a problem.

I expect that part of proc could use an audit where someone figures out
what makes sense.  It does appear that chmod XXX /proc/generic_file
is explicitly supported.  So we would have to be delicate with any
changes in that area to avoid creating userspace regressions.

Eric
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