linux-ext4 - RE: [PATCH v2 4/6] fs: Establish locking order for unrelated directories

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Message-ID: <c5f209a6263b4f039c5eafcafddf90ca@AcuMS.aculab.com>
Date:   Thu, 1 Jun 2023 15:37:32 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Jan Kara' <jack@...e.cz>, Christian Brauner <brauner@...nel.org>
CC:     Al Viro <viro@...IV.linux.org.uk>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Miklos Szeredi <miklos@...redi.hu>,
        "Darrick J. Wong" <djwong@...nel.org>, Ted Tso <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "linux-f2fs-devel@...ts.sourceforge.net" 
        <linux-f2fs-devel@...ts.sourceforge.net>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH v2 4/6] fs: Establish locking order for unrelated
 directories

...
> > > + * Lock any non-NULL argument. The caller must make sure that if he is passing
> > > + * in two directories, one is not ancestor of the other

Not directly relevant to this change but is the 'not an ancestor'
check actually robust?

I found a condition in which the kernel 'pwd' code (which follows
the inode chain) failed to stop at the base of a chroot.

I suspect that the ancestor check would fail the same way.

IIRC the problematic code used unshare() to 'escape' from
a network natespace.
If it was inside a chroot (that wasn't on a mount point) there
ware two copies of the 'chroot /' inode and the match failed.

I might be able to find the test case.

	David

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