Re: [PATCH] ovl: tentative fix for broken vfs_open() on stacked overlayfs.

From	Miklos Szeredi <miklos@szeredi.hu>
Newsgroups	linux.kernel
Subject	Re: [PATCH] ovl: tentative fix for broken vfs_open() on stacked overlayfs.
Date	2016-11-28 10:50 +0100
Message-ID	<sIqJr-lL-7@gated-at.bofh.it> (permalink)
References	<sHq8N-1SA-29@gated-at.bofh.it> <sHsaB-3mU-17@gated-at.bofh.it> <sHum6-4EJ-11@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Fri, Nov 25, 2016 at 08:28:47PM +0100, Quentin Casasnovas wrote:
> On Fri, Nov 25, 2016 at 06:09:23PM +0100, Quentin Casasnovas wrote:
> > If two overlayfs filesystems are stacked on top of each other, then we need
> > to recurse when opening a file.  This used to work and was first broken by:
> > 
> >   4bacc9c9234c ("overlayfs: Make f_path always point to the overlay...")
> > 
> > and fixed by:
> > 
> >   1c8a47df36d7 ("ovl: fix open in stacked overlay")
> > 
> > But it looks like it was re-introduced in:
> > 
> >   2d902671ce1c ("vfs: merge .d_select_inode() into .d_real()")

Thanks for the report.

Following patch should fix it (it's there in your patch, so you weren't too far
off).  It needs more testing and review, but I think it fixes the basic problem.

Thanks,
Miklos


diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index edd46a0e951d..f4d2f63fa53a 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -328,7 +328,7 @@ static struct dentry *ovl_d_real(struct dentry *dentry,
 	if (!real)
 		goto bug;
 
-	if (!inode || inode == d_inode(real))
+	if (inode && inode == d_inode(real))
 		return real;
 
 	/* Handle recursion */

Thread

opening a file on a stacked overlayfs is broken. Quentin Casasnovas <quentin.casasnovas@oracle.com> - 2016-11-25 16:00 +0100
  [PATCH] ovl: tentative fix for broken vfs_open() on stacked overlayfs. Quentin Casasnovas <quentin.casasnovas@oracle.com> - 2016-11-25 18:10 +0100
    Re: [PATCH] ovl: tentative fix for broken vfs_open() on stacked  overlayfs. Quentin Casasnovas <quentin.casasnovas@oracle.com> - 2016-11-25 20:30 +0100
      Re: [PATCH] ovl: tentative fix for broken vfs_open() on stacked  overlayfs. Miklos Szeredi <miklos@szeredi.hu> - 2016-11-28 10:50 +0100
        Re: [PATCH] ovl: tentative fix for broken vfs_open() on stacked  overlayfs. Quentin Casasnovas <quentin.casasnovas@oracle.com> - 2016-11-28 12:10 +0100

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