linux-kernel - Re: [PATCH V2] SELinux: Check correct permissions for FS_IOC32

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Date:   Wed, 6 Sep 2023 13:49:14 -0400
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@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] SELinux: Check correct permissions for FS_IOC32_*

On Wed, Sep 6, 2023 at 7:59 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.
>
> Two possible solutions exist:
>
> - Trim parameter "cmd" to a u16 so that only the last two bytes are
>   checked in the case statement.
>
> - Explicitly add the FS_IOC32_* codes to the case statement.
>
> Solution 2 was chosen because it is a minimal explicit change. Solution
> 1 is a more elegant change, but is less explicit, as the switch
> statement appears to only check the FS_IOC_* codes upon first reading.
>
> Fixes: 0b24dcb7f2f7 ("Revert "selinux: simplify ioctl checking"")
> Signed-off-by: Alfred Piccioni <alpic@...gle.com>
> Cc: stable@...r.kernel.org

Reviewed-by: Stephen Smalley <stephen.smalley.work@...il.com>

> ---
> V1->V2: Cleaned up some typos and added tag for -stable tree inclusion.
>
>  security/selinux/hooks.c | 4 ++++
>  1 file changed, 4 insertions(+)