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: ellyjo...@chromium.org
> Signed-off-by: Kees Cook <keesc...@chromium.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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