[PATCH] Remove file system sharemode before calling unlink

[Christof Schmitt]

On Thu, Jan 11, 2018 at 03:34:47PM -0800, Jeremy Allison wrote:
> On Wed, Jan 10, 2018 at 04:38:29PM -0700, Christof Schmitt via samba-technical wrote:
> > From 05c37256483d961a4448239292022ec38d8ff188 Mon Sep 17 00:00:00 2001
> > From: Christof Schmitt <cs at samba.org>
> > Date: Wed, 10 Jan 2018 15:56:08 -0700
> > Subject: [PATCH] Remove file system sharemode before calling unlink
> > 
> > GPFS implements the DENY_DELETE sharemode, which prevents unlink() from
> > deleting the file.. This causes the problem that deleting a file through
> > "delete on close" fails, as the code in close.c first calls unlink() and
> > only later removes the file system sharemode.
> > 
> > Fix this by removing the file system sharemode before calling unlink().
> 
> Hmmm. This opens up a race that could cause the unlink
> to then fail, if a non-smbd process (i.e. one that ignores
> the tdb share mode lock) opens the path and sets a sharemode
> between the SMB_VFS_KERNEL_FLOCK() and SMB_VFS_UNLINK()
> calls, but I guess failing the unlink in that case is
> also the right thing to do.

Yes. The problem is that unlink() is not tied to the current file
descriptor, so the file system has to treat the unlink() as a sharemode
conflict.  There is nothing like a funlink() call to get around this...

> RB+ and I'll push if I can ever get an autobuild working
> again :-).

Thank you.

Christof