From: Al Viro <viro@zeniv.linux.org.uk>
Date: Fri, 9 May 2008 01:19:42 +0000 (-0400)
Subject: [PATCH] dup_fd() part 4 - race fix
X-Git-Tag: v2.6.26-rc4~115^2~5
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=adbecb128cd2cc5d14b0ebef6d020ced0efd0ec6;p=pandora-kernel.git

[PATCH] dup_fd() part 4 - race fix

Parent _can_ be a clone task, contrary to the comment.  Moreover,
more files could be opened while we allocate a copy, in which case
we end up copying only part into new descriptor table.  Since what
we get _is_ affected by all changes in the old range, we can get
rather weird effects - e.g.
	dup2(0, 1024); close(0);
in parallel with fork() resulting in child that sees the effect of
close(), but not that of dup2() done just before that close().

What we need is to recalculate the open_count after having reacquired
->file_lock and if external fdtable we'd just allocated is too small for
it, free the sucker and redo allocation.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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