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

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Message-ID: <20231012142918.GB255452@mit.edu>
Date:   Thu, 12 Oct 2023 10:29:18 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     Christian Brauner <brauner@...nel.org>,
        Max Kellermann <max.kellermann@...os.com>,
        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 Wed, Oct 11, 2023 at 07:26:06PM +0200, Jan Kara wrote:
> I don't think this is accurate. posix_acl_create() needs unmasked 'mode'
> because instead of using current_umask() for masking it wants to use
> whatever is stored in the ACLs as an umask.
> 
> So I still think we need to keep umask handling in both posix_acl_create()
> and vfs_prepare_mode(). But filesystem's only obligation would be to call
> posix_acl_create() if the inode is IS_POSIXACL. No more caring about when
> to apply umask and when not based on config or mount options.

Ah, right, thanks for the clarification.  I *think* the following
patch in the ext4 dev branch (not yet in Linus's tree, but it should
be in linux-next) should be harmless, though, right?  And once we get
the changes in vfs_prepare_mode() we can revert in ext4 --- or do
folks I think I should just drop it from the ext4 dev branch now?

Thanks,

						- Ted

commit 484fd6c1de13b336806a967908a927cc0356e312
Author: Max Kellermann <max.kellermann@...os.com>
Date:   Tue Sep 19 10:18:23 2023 +0200

    ext4: apply umask if ACL support is disabled
    
    The function ext4_init_acl() calls posix_acl_create() which is
    responsible for applying the umask.  But without
    CONFIG_EXT4_FS_POSIX_ACL, ext4_init_acl() is an empty inline function,
    and nobody applies the umask.
    
    This fixes a bug which causes the umask to be ignored with O_TMPFILE
    on ext4:
    
     https://github.com/MusicPlayerDaemon/MPD/issues/558
     https://bugs.gentoo.org/show_bug.cgi?id=686142#c3
     https://bugzilla.kernel.org/show_bug.cgi?id=203625
    
    Reviewed-by: "J. Bruce Fields" <bfields@...hat.com>
    Cc: stable@...r.kernel.org
    Signed-off-by: Max Kellermann <max.kellermann@...os.com>
    Link: https://lore.kernel.org/r/20230919081824.1096619-1-max.kellermann@ionos.com
    Signed-off-by: Theodore Ts'o <tytso@....edu>

diff --git a/fs/ext4/acl.h b/fs/ext4/acl.h
index 0c5a79c3b5d4..ef4c19e5f570 100644
--- a/fs/ext4/acl.h
+++ b/fs/ext4/acl.h
@@ -68,6 +68,11 @@ extern int ext4_init_acl(handle_t *, struct inode *, struct inode *);
 static inline int
 ext4_init_acl(handle_t *handle, struct inode *inode, struct inode *dir)
 {
+	/* usually, the umask is applied by posix_acl_create(), but if
+	   ext4 ACL support is disabled at compile time, we need to do
+	   it here, because posix_acl_create() will never be called */
+	inode->i_mode &= ~current_umask();
+
 	return 0;
 }
 #endif  /* CONFIG_EXT4_FS_POSIX_ACL */