[PATCH] security: new security_file_ioctl_compat() hook

[Paul Moore]

On Tue, Dec 19, 2023 at 4:09 AM Alfred Piccioni <alpic at google.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 syscall. 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 at google.com>
> Cc: stable at vger.kernel.org
> ---
>  fs/ioctl.c                    |  3 +--
>  include/linux/lsm_hook_defs.h |  2 ++
>  include/linux/security.h      |  7 +++++++
>  security/security.c           | 17 +++++++++++++++++
>  security/selinux/hooks.c      | 28 ++++++++++++++++++++++++++++
>  security/smack/smack_lsm.c    |  1 +
>  security/tomoyo/tomoyo.c      |  1 +
>  7 files changed, 57 insertions(+), 2 deletions(-)

I made some minor style tweaks around line length and alignment, but
otherwise this looked good to me.  Thanks all!

While I agree this is definitely stable kernel material, given where
we are at in the current kernel cycle, and with the end-of-year
holidays in full swing, I'm going to merge this into lsm/dev and send
it up to Linus during the next merge window.  The stable tag will
remain intact, so it will end up trickling down into the stable
kernels, it will just take an extra week or so (which I think will be
good from a testing perspective).

-- 
paul-moore.com