linux-ext4 - Re: [PATCH v2] fs/{posix_acl,ext2,jfs,ceph}: apply umask if ACL support is disabled

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Date: Fri, 15 Mar 2024 14:52:24 +0100
From: Christian Brauner <brauner@...nel.org>
To: Max Kellermann <max.kellermann@...os.com>
Cc: Michael Forney <mforney@...rney.org>, Jan Kara <jack@...e.cz>, 
	Theodore Ts'o <tytso@....edu>, Xiubo Li <xiubli@...hat.com>, Ilya Dryomov <idryomov@...il.com>, 
	Jeff Layton <jlayton@...nel.org>, Jan Kara <jack@...e.com>, Dave Kleikamp <shaggy@...nel.org>, 
	ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org, 
	jfs-discussion@...ts.sourceforge.net, Yang Xu <xuyang2018.jy@...itsu.com>, 
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2] fs/{posix_acl,ext2,jfs,ceph}: apply umask if ACL
 support is disabled

On Thu, Mar 14, 2024 at 02:08:04PM +0100, Max Kellermann wrote:
> On Wed, Mar 13, 2024 at 9:39 PM Michael Forney <mforney@...rney.org> wrote:
> > Turns out that symlinks are inheriting umask on my system (which
> > has CONFIG_EXT4_FS_POSIX_ACL=n):
> >
> > $ umask 022
> > $ ln -s target symlink
> > $ ls -l symlink
> > lrwxr-xr-x    1 michael  michael           6 Mar 13 13:28 symlink -> target
> > $
> >
> > Looking at the referenced functions, posix_acl_create() returns
> > early before applying umask for symlinks, but ext4_init_acl() now
> > applies the umask unconditionally.
> 
> Indeed, I forgot to exclude symlinks from this - sorry for the breakage.
> 
> > After reverting this commit, it works correctly. I am also unable
> > to reproduce the mentioned issue with O_TMPFILE after reverting the
> > commit. It seems that the bug was fixed properly in ac6800e279a2
> > ('fs: Add missing umask strip in vfs_tmpfile'), and all branches
> > that have this ext4_init_acl patch already had ac6800e279a2 backported.
> 
> I can post a patch that adds the missing check or a revert - what do
> the FS maintainers prefer?

If it works correctly with a revert we should remove the code rather
than adding more code to handle a special case.

> 
> (There was a bug with O_TMPFILE ignoring umasks years ago - I first
> posted the patch in 2018 or so - but by the time my patch actually got
> merged, the bug had already been fixed somewhere else IIRC.)

Yeah, we fixed it a while ago and then I added generic VFS level umask
handling but POSIX ACL are hurting us because they're a massive layering
violation on that front.