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

Theodore Ts'o
2023-10-12T14:30:17Z

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@ionos.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@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
Link: https://lore.kernel.org/r/20230919081824.1096619-1-max.kellermann@ionos.com
Signed-off-by: Theodore Ts'o <tytso@mit.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 */