On Fri, Nov 16, 2012 at 4:27 PM, Greg Kroah-Hartman
<gre...@linuxfoundation.org> wrote:
> 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?
It doesn't break Chrome OS nor my test VM. The logic for building
/etc/mtab needs updating (it doesn't show nosuid,noexec), but
/proc/mounts reports it correctly.
-Kees
>
> 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
--
Kees Cook
Chrome OS Security
--
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