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Message-ID: <21585.1487776675@warthog.procyon.org.uk> Date: Wed, 22 Feb 2017 15:17:55 +0000 From: David Howells <dhowells@...hat.com> To: unlisted-recipients:; (no To-header on input) Cc: dhowells@...hat.com, viro@...IV.linux.org.uk, linux-kernel@...r.kernel.org, Seth Forshee <seth.forshee@...onical.com>, "Eric W. Biederman" <ebiederm@...ssion.com>, linux-fsdevel@...r.kernel.org, linux-afs@...ts.infradead.org Subject: Re: [PATCH] vfs: Partially revert addition of cred override in follow_automount() David Howells <dhowells@...hat.com> wrote: > The following commit: > > commit aeaa4a79ff6a5ed912b7362f206cf8576fca538b > Author: Eric W. Biederman <ebiederm@...ssion.com> > Date: Sat Jul 23 11:20:44 2016 -0500 > fs: Call d_automount with the filesystems creds > > brackets the call to ->d_automount() with override_creds() and > revert_creds(), setting the initial credentials for use whilst > automounting. > > This, however, breaks AFS as it's no longer able to access the calling > process's keyrings to read the destination on a mountpoint. This has gone > unnoticed till now because, to this point, stat'ing or validating the inode > caused the body of the mountpoint to be read into the pagecache (so that we > could determine whether what we were looking at was really a mountpoint). > > However, the page containing the mountpoint destination is merely *cached* > and not pinned. If it gets discarded and we try to read it in d_automount, > we may fail because we have no authentication tokens available. > > So, for the moment, revert the addition of override_creds() and > revert_creds() and their variable. > > Fixes: aeaa4a79ff6a ("fs: Call d_automount with the filesystems creds") > Signed-off-by: David Howells <dhowells@...hat.com> > cc: Seth Forshee <seth.forshee@...onical.com> > cc: "Eric W. Biederman" <ebiederm@...ssion.com> > cc: Al Viro <viro@...IV.linux.org.uk> This is also resolved by: https://git.kernel.org/cgit/linux/kernel/git/ebiederm/user-namespace.git/commit/?h=for-next&id=93faccbbfa958a9668d3ab4e30f38dd205cee8d8 David
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