Re: [PATCH] SELinux: Introduce security_file_ioctl_compat hook

From: Stephen Smalley <stephen.smalley.work@gmail.com>
To: Casey Schaufler <casey@schaufler-ca.com>
Cc: Alfred Piccioni <alpic@google.com>,
	Paul Moore <paul@paul-moore.com>,
	 Eric Paris <eparis@parisplace.org>,
	stable@vger.kernel.org, selinux@vger.kernel.org,
	 linux-kernel@vger.kernel.org
Subject: Re: [PATCH] SELinux: Introduce security_file_ioctl_compat hook
Date: Mon, 18 Dec 2023 12:36:31 -0500	[thread overview]
Message-ID: <CAEjxPJ4tZAvch50i7Ve_7dPYUzCXK8ckDtmhwq81vjCf7pweQw@mail.gmail.com> (raw)
In-Reply-To: <6dce3020-14f0-471b-9b6a-c9dc761cfa19@schaufler-ca.com>

On Mon, Dec 18, 2023 at 12:11 PM Casey Schaufler <casey@schaufler-ca.com> wrote:
>
> On 12/18/2023 6:16 AM, Alfred Piccioni wrote:
>
> > Some ioctl commands do not require ioctl permission, but are routed to
> > other permissions such as FILE_GETATTR or FILE_SETATTR. This routing is
> > done by comparing the ioctl cmd to a set of 64-bit flags (FS_IOC_*).
> >
> > However, if a 32-bit process is running on a 64-bit kernel, it emits
> > 32-bit flags (FS_IOC32_*) for certain ioctl operations. These flags are
> > being checked erroneously, which leads to these ioctl operations being
> > routed to the ioctl permission, rather than the correct file
> > permissions.
> >
> > This was also noted in a RED-PEN finding from a while back -
> > "/* RED-PEN how should LSM module know it's handling 32bit? */".
> >
> > This patch introduces a new hook, security_file_ioctl_compat, that is
> > called from the compat ioctl syscal. All current LSMs have been changed
> > to support this hook.
> >
> > Reviewing the three places where we are currently using
> > security_file_ioctl, it appears that only SELinux needs a dedicated
> > compat change; TOMOYO and SMACK appear to be functional without any
> > change.
> >
> > Fixes: 0b24dcb7f2f7 ("Revert "selinux: simplify ioctl checking"")
> > Signed-off-by: Alfred Piccioni <alpic@google.com>
> > Cc: stable@vger.kernel.org
>
> This *really* needs to go the the LSM email list:
>         linux-security-module@vger.kernel.org

Yep, pointed that out a little earlier in this thread.

> > ---
> > diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
> > index ac962c4cb44b..626aa8cf930d 100644
> > --- a/include/linux/lsm_hook_defs.h
> > +++ b/include/linux/lsm_hook_defs.h
> > @@ -171,6 +171,8 @@ LSM_HOOK(int, 0, file_alloc_security, struct file *file)
> >  LSM_HOOK(void, LSM_RET_VOID, file_free_security, struct file *file)
> >  LSM_HOOK(int, 0, file_ioctl, struct file *file, unsigned int cmd,
> >        unsigned long arg)
> > +LSM_HOOK(int, 0, file_ioctl_compat, struct file *file, unsigned int cmd,
> > +      unsigned long arg)
>
> Please add a flags parameter to file_ioctl() rather than a new hook.

Paul told him the opposite earlier.