linux-kernel - Re: [git pull] apparmor fix for __d

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Message-Id: <201112070544.pB75iX12072157@www262.sakura.ne.jp>
Date:	Wed, 07 Dec 2011 14:44:33 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	viro@...IV.linux.org.uk
Cc:	john.johansen@...onical.com, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, torvalds@...ux-foundation.org
Subject: Re: [git pull] apparmor fix for __d_path() misuse

Al Viro wrote:
> > So, can we keep behavior of tomoyo_get_absolute_path() unchanged?
> 
> Sure, you are always free to add
> 	if (pos == ERR_PTR(-EINVAL)) {
> 		pos = dentry_path(path->dentry, ...)
> 		/* do whatever you want to buffer to indicate that
> 		 * beginning had been lost
> 		 */
> 	}

Maybe I can call tomoyo_get_local_path() if tomoyo_get_absolute_path() failed
with -EINVAL.

> Or you might want to do __d_path() from (path->mnt,path->mnt->mnt_root) to
> path - that's the path from the last mountpoint to your object; i.e. it may
> be shorter if that vfsmount had been a binding into the guts of filesystem,
> but that is what __d_path() as you used it would stabilize to once the race
> window is over.

Excuse me, what "once the race window is over" means?
Does

  do {
    pos = d_absolute_path(path, buffer, buflen - 1);
  } while (pos == ERR_PTR(-EINVAL));

work (i.e. racing with "umount -l" is a temporary failure)?
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