Message-ID: <CAEjxPJ40jPsBS5xZEgS1CCVYORDJhwNOrAj5Oepa3rK=Y1BnYg@mail.gmail.com>
Date: Mon, 18 Dec 2023 10:58:33 -0500
From: Stephen Smalley <stephen.smalley.work@...il.com>
To: Alfred Piccioni <alpic@...gle.com>
Cc: Paul Moore <paul@...l-moore.com>, Eric Paris <eparis@...isplace.org>, stable@...r.kernel.org, 
	SElinux list <selinux@...r.kernel.org>, linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] SELinux: Introduce security_file_ioctl_compat hook

On Mon, Dec 18, 2023 at 9:17 AM Alfred Piccioni <alpic@...gle.com> 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

s/syscal/syscall/
Might to consider checking using codespell to catch such things
although it is imperfect.

> 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@...gle.com>
> Cc: stable@...r.kernel.org
> ---

> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 2aa0e219d721..de96d156e6ea 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -3731,6 +3731,31 @@ static int selinux_file_ioctl(struct file *file, unsigned int cmd,
>         return error;
>  }
>
> +static int selinux_file_ioctl_compat(struct file *file, unsigned int cmd,
> +                             unsigned long arg)
> +{
> +       // If we are in a 64-bit kernel running 32-bit userspace, we need to make
> +       // sure we don't compare 32-bit flags to 64-bit flags.

Paul doesn't like C++-style comments so rewrite using kernel coding
style for multi-line comments or drop.
I don't think kernel coding style strictly prohibits use for
single-line comments and it isn't detected by checkpatch.pl but he has
previously
raised this on other patches. I actually like the C++-style comments
for one-liners especially for comments at the end of a line of code
but Paul is the maintainer so he gets the final word.

> +       switch (cmd) {
> +       case FS_IOC32_GETFLAGS:
> +               cmd = FS_IOC_GETFLAGS;
> +               break;
> +       case FS_IOC32_SETFLAGS:
> +               cmd = FS_IOC_GETFLAGS;

Sorry, missed this the first time but cut-and-paste error above:
s/GETFLAGS/SETFLAGS/

I didn't do an audit but does anything need to be updated for the BPF
LSM or does it auto-magically pick up new hooks?

Also, IIRC, Paul prefers putting a pair of parentheses after function
names to distinguish them, so in the subject line
and description it should be security_file_ioctl_compat() and
security_file_ioctl(), and you should put a patch version
in the [PATCH] prefix e.g. [PATCH v3] to make clear that it is a later
version, and usually one doesn't capitalize SELinux
or the leading verb in the subject line (just "selinux: introduce").

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