linux-kernel - Re: [PATCH] swapon: check validity of swap

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Message-ID: <alpine.LSU.2.00.1203231416260.2235@eggly.anvils>
Date:	Fri, 23 Mar 2012 14:20:27 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Al Viro <viro@...iv.linux.org.uk>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] swapon: check validity of swap_flags

On Fri, 23 Mar 2012, Andrew Morton wrote:
> On Fri, 23 Mar 2012 13:48:35 -0700 (PDT)
> Hugh Dickins <hughd@...gle.com> wrote:
> 
> > Most system calls taking flags first check that the flags passed in are
> > valid, and that helps userspace to detect when new flags are supported.
> > 
> > But swapon never did so: start checking now, to help if we ever want to
> > support more swap_flags in future.
> > 
> > It's difficult to get stray bits set in an int, and swapon is not widely
> > used, so this is most unlikely to break any userspace; but we can just
> > revert if it turns out to do so.
> 
> It would be safer to emit a nasty message then let the swapon proceed
> as before.

Safer, I suppose, but I really don't expect that case to arise (we'll
have been doing those lovely runtime discards without asking for a year
now if so).  And it does spoil the checking of supported flags.

Hugh
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