fs: Call security_ops->inode_killpriv on truncate

fs: Call security_ops->inode_killpriv on truncate

From 45f147a1bc97c743c6101a8d2741c69a51f583e4 Mon Sep 17 00:00:00 2001

Comment in include/linux/security.h says that ->inode_killpriv() should
be called when setuid bit is being removed and that similar security
labels (in fact this applies only to file capabilities) should be
removed at this time as well. However we don't call ->inode_killpriv()
when we remove suid bit on truncate.

We fix the problem by calling ->inode_need_killpriv() and subsequently
->inode_killpriv() on truncate the same way as we do it on file write.

After this patch there's only one user of should_remove_suid() - ocfs2 -
and indeed it's buggy because it doesn't call ->inode_killpriv() on
write. However fixing it is difficult because of special locking
constraints.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Orabug: 24803533
Signed-off-by: darrick.wong@oracle.com