linux-ext4 - Re: [PATCH] ext4: Give 32bit personalities 32bit hashes

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: <CAFEAcA_6RY1XFVNJCo5=tTkv2GQpXZRqh_Zz4dYadq-8MJZgTQ@mail.gmail.com>
Date:   Tue, 24 Mar 2020 09:29:58 +0000
From:   Peter Maydell <peter.maydell@...aro.org>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        "Suzuki K. Poulose" <suzuki.poulose@....com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        QEMU Developers <qemu-devel@...gnu.org>,
        Florian Weimer <fw@...eb.enyo.de>,
        Andy Lutomirski <luto@...nel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH] ext4: Give 32bit personalities 32bit hashes

On Tue, 24 Mar 2020 at 02:34, Theodore Y. Ts'o <tytso@....edu> wrote:
> Another possibility, which would be messier for qemu, would be use a
> flag set via fcntl.  That would require qemu from noticing when the
> guest is calling open, openat, or openat2, and then inserting a fcntl
> system call to set the 32-bit readdir mode.  That's cleaner from the
> kernel interface complexity perspective, but it's messier for qemu.

On the contrary, that would be a much better interface for QEMU.
We always know when we're doing an open-syscall on behalf
of the guest, and it would be trivial to make the fcntl() call then.
That would ensure that we don't accidentally get the
'32-bit semantics' on file descriptors QEMU opens for its own
purposes, and wouldn't leave us open to the risk in future that
setting the PER_LINUX32 flag for all of QEMU causes
unexpected extra behaviour in future kernels that would be correct
for the guest binary but wrong/broken for QEMU's own internals.

thanks
-- PMM