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From: Al Viro <viro@ZenIV.linux.org.uk>
To: NeilBrown <neilb@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Christoph Hellwig <hch@lst.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Eric Biederman <ebiederm@xmission.com>
Subject: Re: dcache: remove trylock loops (was Re: [BUG] lock_parent() breakage when used from shrink_dentry_list())
Date: Sat, 28 Apr 2018 01:10:03 +0100	[thread overview]
Message-ID: <20180428001003.GA14907@ZenIV.linux.org.uk> (raw)
In-Reply-To: <87o9jsdbho.fsf@notabene.neil.brown.name>

On Tue, Mar 13, 2018 at 12:12:51PM +1100, NeilBrown wrote:

> >	     * selinux inode_doinit_with_dentry() (two call sites, very alike)
> 
> I'm less sure about this one, but I think it probably wants
> d_find_any_alias() as well.  Like cap_inode_getsecurity() it only wants
> a dentry so that it can pass something to __vfs_getxattr(),
> and that only wants a dentry so it can pass something to ->get.
> 
> Possibly we should rename d_find_alias() to d_find_hashed_alias() so that
> people need to make a conscious choice between d_find_hashed_alias() and
> d_find_any_alias() ??

FWIW, it *is* a bug; this
                        /*
                         * this is can be hit on boot when a file is accessed
                         * before the policy is loaded.  When we load policy we
                         * may find inodes that have no dentry on the
                         * sbsec->isec_head list.  No reason to complain as these
                         * will get fixed up the next time we go through
                         * inode_doinit with a dentry, before these inodes could
                         * be used again by userspace.
                         */
in selinux/hooks.c is flat-out wrong now.  Sure, if you first load selinux
policy after exporting something over NFS or letting attacker play with
open-by-fhandle, you are past any help, but still...

I disagree about going for d_find_any_alias() from the very beginning, BTW -
we need to try it in case of d_find_alias() failure, but sufficiently crappy
filesystem can bloody well fail to access xattrs via disconnected dentry.

  reply	other threads:[~2018-04-28  0:10 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-22 23:50 [PATCH v2 0/6] fs/dcache: avoid trylock loops John Ogness
2018-02-22 23:50 ` [PATCH v2 1/6] fs/dcache: Remove stale comment from dentry_kill() John Ogness
2018-02-22 23:50 ` [PATCH v2 2/6] fs/dcache: Move dentry_kill() below lock_parent() John Ogness
2018-02-22 23:50 ` [PATCH v2 3/6] fs/dcache: Avoid the try_lock loop in d_delete() John Ogness
2018-02-23  2:08   ` Al Viro
2018-02-22 23:50 ` [PATCH v2 4/6] fs/dcache: Avoid the try_lock loops in dentry_kill() John Ogness
2018-02-23  2:22   ` Al Viro
2018-02-23  3:12     ` Al Viro
2018-02-23  3:16       ` Al Viro
2018-02-23  5:46       ` Al Viro
2018-02-22 23:50 ` [PATCH v2 5/6] fs/dcache: Avoid a try_lock loop in shrink_dentry_list() John Ogness
2018-02-23  3:48   ` Al Viro
2018-02-22 23:50 ` [PATCH v2 6/6] fs/dcache: Avoid remaining " John Ogness
2018-02-23  3:58   ` Al Viro
2018-02-23  4:08     ` Al Viro
2018-02-23 13:57       ` John Ogness
2018-02-23 15:09         ` Al Viro
2018-02-23 17:42           ` Al Viro
2018-02-23 20:13             ` [BUG] lock_parent() breakage when used from shrink_dentry_list() (was Re: [PATCH v2 6/6] fs/dcache: Avoid remaining try_lock loop in shrink_dentry_list()) Al Viro
2018-02-23 21:35               ` Linus Torvalds
2018-02-24  0:22                 ` Al Viro
2018-02-25  7:40                   ` Al Viro
2018-02-27  5:16                     ` dcache: remove trylock loops (was Re: [BUG] lock_parent() breakage when used from shrink_dentry_list()) John Ogness
2018-03-12 19:13                       ` Al Viro
2018-03-12 20:05                         ` Al Viro
2018-03-12 20:33                           ` Al Viro
2018-03-13  1:12                           ` NeilBrown
2018-04-28  0:10                             ` Al Viro [this message]
2018-03-12 20:23                         ` Eric W. Biederman
2018-03-12 20:39                           ` Al Viro
2018-03-12 23:28                             ` Eric W. Biederman
2018-03-12 23:52                               ` Eric W. Biederman
2018-03-13  0:37                                 ` Al Viro
2018-03-13  0:50                                   ` Al Viro
2018-03-13  4:02                                     ` Eric W. Biederman
2018-03-14 23:20                                     ` [PATCH] fs: Teach path_connected to handle nfs filesystems with multiple roots Eric W. Biederman
2018-03-15 22:34                                       ` Al Viro
2018-03-13  0:36                               ` dcache: remove trylock loops (was Re: [BUG] lock_parent() breakage when used from shrink_dentry_list()) Al Viro
2018-03-12 22:14                         ` Thomas Gleixner
2018-03-13 20:46                         ` John Ogness
2018-03-13 21:05                           ` John Ogness
2018-03-13 23:59                             ` Al Viro
2018-03-14  2:58                               ` Matthew Wilcox
2018-03-14  8:18                               ` John Ogness
2018-03-02  9:04                     ` [BUG] lock_parent() breakage when used from shrink_dentry_list() (was Re: [PATCH v2 6/6] fs/dcache: Avoid remaining try_lock loop in shrink_dentry_list()) Sebastian Andrzej Siewior
2018-02-23  0:59 ` [PATCH v2 0/6] fs/dcache: avoid trylock loops Linus Torvalds

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