[PATCH] security: new security_file_ioctl_compat() hook

[Stephen Smalley]

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
> ---

Reviewed-by: Stephen Smalley <stephen.smalley.work at gmail.com>