linux-kernel - Re: [PATCH -next 2/3] batman-adv: Use seq

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Message-ID: <20131211080504.GT10323@ZenIV.linux.org.uk>
Date:	Wed, 11 Dec 2013 08:05:04 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Joe Perches <joe@...ches.com>
Cc:	Kees Cook <keescook@...omium.org>,
	Marek Lindner <mareklindner@...mailbox.ch>,
	Simon Wunderlich <sw@...onwunderlich.de>,
	Antonio Quartulli <antonio@...hcoding.com>,
	"David S. Miller" <davem@...emloft.net>,
	b.a.t.m.a.n@...ts.open-mesh.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next 2/3] batman-adv: Use seq_overflow

On Wed, Dec 11, 2013 at 07:55:26AM +0000, Al Viro wrote:

> This sucker should return 0.  Insufficiently large buffer will be handled
> by caller, TYVM, if you give that caller a chance to do so.  Returning 1
> from ->show() is a bug in almost all cases, and definitely so in this one.
> 
> Just in case somebody decides that above is worth copying: It Is Not.
> Original code is buggy, plain and simple.  This one trades the older
> bug ("fail with -EINVAL whenever the buffer is too small") with just as buggy
> "silently skip an entry entirely whenever the buffer is too small".
> 
> Don't Do That.

Pardon - Joe has made seq_overflow return -1 instead of true.  Correction
to the above, then - s/This trades.*\./This is just as buggy./

Conclusion is still the same - Don't Do That.  Returning -1 on insufficiently
large buffer is a bug, plain and simple.

And this patch series is completely misguided - it doesn't fix any bugs
*and* it provides a misleading example for everyone.  See the reaction
right in this thread, proposing to spread the same bug to currently
working iterators.
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