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From: Stephen Smalley <stephen.smalley.work@gmail.com>
Date: Mon, 18 Dec 2023 08:46:58 -0500
Message-ID: <CAEjxPJ6G7gHi=kLmgT3m1kDQeTpT1xLexDXbZRBMjJdiWrx=mw@mail.gmail.com>
Subject: Re: [PATCH] SELinux: Introduce security_file_ioctl_compat hook
To: Alfred Piccioni <alpic@google.com>
Cc: Paul Moore <paul@paul-moore.com>, Eric Paris <eparis@parisplace.org>, stable@vger.kernel.org, 
	selinux@vger.kernel.org, linux-kernel@vger.kernel.org
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On Mon, Dec 18, 2023 at 7:43=E2=80=AFAM Alfred Piccioni <alpic@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 emmits

s/emmits/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
> replaces security_file_ioctl if the CONFIG_COMPAT flag is on. All
> current LSMs have been changed to hook into the compat flag.

It doesn't (or shouldn't) replace security_file_ioctl, and the hook
doesn't appear to be conditional on CONFIG_COMPAT per se.
It is a new hook that is called from the compat ioctl syscall. The old
hook continues to be used from the regular ioctl syscall and
elsewhere.

> 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
> ---
> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> index 83ef66644c21..170687b5985b 100644
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -751,7 +751,11 @@ static int ovl_security_fileattr(const struct path *=
realpath, struct fileattr *f
>         else
>                 cmd =3D fa->fsx_valid ? FS_IOC_FSGETXATTR : FS_IOC_GETFLA=
GS;
>
> +#ifdef CONFIG_COMPAT
> +       err =3D security_file_ioctl_compat(file, cmd, 0);
> +# else
>         err =3D security_file_ioctl(file, cmd, 0);
> +#endif

I don't understand why you made this change, possibly a leftover of an
earlier version of the patch that tried to replace
security_file_ioctl() everywhere?