From: Miklos Szeredi <miklos@szeredi.hu>
Date: Thu, 5 Sep 2013 12:39:11 +0000 (+0200)
Subject: vfs: check unlinked ancestors before mount
X-Git-Tag: v3.12-rc1~105^2~8
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=eed810076685c77dc9a8c5c3593e641c93caed1c;p=pandora-kernel.git

vfs: check unlinked ancestors before mount

We check submounts before doing d_drop() on a non-empty directory dentry in
NFS (have_submounts()), but we do not exclude a racing mount.  Nor do we
prevent mounts to be added to the disconnected subtree using relative paths
after the d_drop().

This patch fixes these issues by checking for unlinked (unhashed, non-root)
ancestors before proceeding with the mount.  This is done with rename
seqlock taken for write and with ->d_lock grabbed on each ancestor in turn,
including our dentry itself.  This ensures that the only one of
check_submounts_and_drop() or has_unlinked_ancestor() can succeed.

Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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