linux-kernel - Re: [PATCH] devtmpfs: mount with noexec and nosuid

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Date:	Fri, 16 Nov 2012 16:27:53 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Kees Cook <keescook@...omium.org>, Kay Sievers <kay@...y.org>
Cc:	linux-kernel@...r.kernel.org, ellyjones@...omium.org
Subject: Re: [PATCH] devtmpfs: mount with noexec and nosuid

On Fri, Nov 16, 2012 at 04:20:16PM -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"), with a system
> that already has nosuid,noexec on all other writable mounts.
> 
> Cc: ellyjones@...omium.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  drivers/base/devtmpfs.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)

Have you tested this to verify that it doesn't break anything?

Kay, could this cause any problems that you could think of?

thanks,

greg k-h

> 
> diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
> index 147d1a4..b7e2e57 100644
> --- a/drivers/base/devtmpfs.c
> +++ b/drivers/base/devtmpfs.c
> @@ -340,6 +340,7 @@ static int handle_remove(const char *nodename, struct device *dev)
>  int devtmpfs_mount(const char *mntdir)
>  {
>  	int err;
> +	int mflags = MS_SILENT | MS_NOEXEC | MS_NOSUID;
>  
>  	if (!mount_dev)
>  		return 0;
> @@ -347,7 +348,7 @@ int devtmpfs_mount(const char *mntdir)
>  	if (!thread)
>  		return 0;
>  
> -	err = sys_mount("devtmpfs", (char *)mntdir, "devtmpfs", MS_SILENT, NULL);
> +	err = sys_mount("devtmpfs", (char *)mntdir, "devtmpfs", mflags, NULL);
>  	if (err)
>  		printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
>  	else
> @@ -368,11 +369,12 @@ static int handle(const char *name, umode_t mode, struct device *dev)
>  static int devtmpfsd(void *p)
>  {
>  	char options[] = "mode=0755";
> +	int mflags = MS_SILENT | MS_NOEXEC | MS_NOSUID;
>  	int *err = p;
>  	*err = sys_unshare(CLONE_NEWNS);
>  	if (*err)
>  		goto out;
> -	*err = sys_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, options);
> +	*err = sys_mount("devtmpfs", "/", "devtmpfs", mflags, options);
>  	if (*err)
>  		goto out;
>  	sys_chdir("/.."); /* will traverse into overmounted root */
> -- 
> 1.7.9.5
> 
> 
> -- 
> Kees Cook
> Chrome OS Security
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