linux-kernel - Re: [RFC PATCH 1/4] fs: Add FS_XFLAG_COMPRESSED & FS_XFLAG_ENCRYPTED for FS_IOC

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAOQ4uxigYpzpttfaRc=xAxJc=f2bz89_eCideuftf3egTiE+3A@mail.gmail.com>
Date: Sun, 16 Feb 2025 21:17:55 +0100
From: Amir Goldstein <amir73il@...il.com>
To: Eric Biggers <ebiggers@...nel.org>, Pali Rohár <pali@...nel.org>
Cc: "Darrick J. Wong" <djwong@...nel.org>, ronnie sahlberg <ronniesahlberg@...il.com>, 
	Chuck Lever <chuck.lever@...cle.com>, Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
	Steve French <sfrench@...ba.org>, Alexander Viro <viro@...iv.linux.org.uk>, 
	linux-fsdevel@...r.kernel.org, linux-cifs@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/4] fs: Add FS_XFLAG_COMPRESSED & FS_XFLAG_ENCRYPTED
 for FS_IOC_FS[GS]ETXATTR API

On Sun, Feb 16, 2025 at 7:34 PM Eric Biggers <ebiggers@...nel.org> wrote:
>
> On Sun, Feb 16, 2025 at 05:40:26PM +0100, Pali Rohár wrote:
> > This allows to get or set FS_COMPR_FL and FS_ENCRYPT_FL bits via FS_IOC_FSGETXATTR/FS_IOC_FSSETXATTR API.
> >
> > Signed-off-by: Pali Rohár <pali@...nel.org>
>
> Does this really allow setting FS_ENCRYPT_FL via FS_IOC_FSSETXATTR, and how does
> this interact with the existing fscrypt support in ext4, f2fs, ubifs, and ceph
> which use that flag?

As far as I can tell, after fileattr_fill_xflags() call in
ioctl_fssetxattr(), the call
to ext4_fileattr_set() should behave exactly the same if it came some
FS_IOC_FSSETXATTR or from FS_IOC_SETFLAGS.
IOW, EXT4_FL_USER_MODIFIABLE mask will still apply.

However, unlike the legacy API, we now have an opportunity to deal with
EXT4_FL_USER_MODIFIABLE better than this:
        /*
         * chattr(1) grabs flags via GETFLAGS, modifies the result and
         * passes that to SETFLAGS. So we cannot easily make SETFLAGS
         * more restrictive than just silently masking off visible but
         * not settable flags as we always did.
         */

if we have the xflags_mask in the new API (not only the xflags) then
chattr(1) can set EXT4_FL_USER_MODIFIABLE in xflags_mask
ext4_fileattr_set() can verify that
(xflags_mask & ~EXT4_FL_USER_MODIFIABLE == 0).

However, Pali, this is an important point that your RFC did not follow -
AFAICT, the current kernel code of ext4_fileattr_set() and xfs_fileattr_set()
(and other fs) does not return any error for unknown xflags, it just
ignores them.

This is why a new ioctl pair FS_IOC_[GS]ETFSXATTR2 is needed IMO
before adding support to ANY new xflags, whether they are mapped to
existing flags like in this patch or are completely new xflags.

Thanks,
Amir.