Re: [PATCH v2] devtmpfs: mount with noexec and nosuid

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Nov 20, 2012 at 12:42:38PM -0800, Kees Cook wrote:
> Since devtmpfs is writable, make the default noexec,nosuid as well. This
> protects from the case of a privileged process having an arbitrary file
> write flaw and an argumentless arbitrary execution (i.e. it would lack
> the ability to run "mount -o remount,exec,suid /dev").
> 
> Cc: ellyjones@chromium.org
> Cc: Kay Sievers <kay@vrfy.org>
> Cc: Roland Eggner <edvx1@systemanalysen.net>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> 
> ---
> v2:
> - use CONFIG_DEVTMPFS_SAFE to wrap the logic.

That's better, thanks.

One tiny bikeshead request though:

> --- a/drivers/base/devtmpfs.c
> +++ b/drivers/base/devtmpfs.c
> @@ -340,6 +340,10 @@ static int handle_remove(const char *nodename, struct device *dev)
>  int devtmpfs_mount(const char *mntdir)
>  {
>  	int err;
> +	int mflags = MS_SILENT;
> +#ifdef CONFIG_DEVTMPFS_SAFE
> +	mflags |= MS_NOEXEC | MS_NOSUID;
> +#endif

You duplicate this in two places, which makes the c code harder to read.
How about, at the top of the file, you do:

#ifdef CONFIG_DEVTMPFS_SAFE
#define DEVTMPFS_MFLAGS	MS_SILENT | MS_NOEXEC | MS_NOSUID
#else
#define DEVTMPFS_MFLAGS	MS_SILENT
#endif

And then just use DEVTMPFS_MFLAGS in both places?

That should make the patch smaller, which is always nice :)

thanks,

greg k-h