Re: /proc/sys/kernel/pty/nr broken, possibly since 2.6.28

From: H. Peter Anvin
Date: Thu Nov 05 2009 - 20:04:21 EST

On 11/05/2009 03:51 PM, H. Peter Anvin wrote:
> I just noticed that /proc/sys/kernel/pty/nr is broken, and the most
> likely culprit seems to be the series of checkins that include 8b0a88d5
> and bf970ee4, during the 2.6.28 merge window. This is thus a
> regression. I haven't verified that the bug really goes that far back
> -- I should do a bisection -- but it is at least present in and
> 2.6.32-rc6.
> The symptom is that /proc/sys/kernel/pty/nr is properly increased, but
> never decreased when a pty gets dropped. It is in fact rather trivial
> to escalate /proc/sys/kernel/pty/nr far above /proc/sys/kernel/pty/max.
> As far as I read this series, the indent was to have this accounting
> handled in pty_unix98_remove(), however, it would appear that that
> function never gets called. I'm wondering if this may be a symptom of a
> bigger problem as well.

Bisection confirms that the bug was introduced during this commit series:

There are only 'skip'ped commit left to test.
The first bad commit could be any of:
We cannot bisect more!

This series of skipped commits are ones during which
/proc/sys/kernel/pty doesn't exist at all.

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