The devcgroup_inode_permission() hook in the devices whitelist
cgroup has always bypassed access checks on fifos. But the
mknod hook did not. The devices whitelist is only about block
and char devices, and fifos can't even be added to the whitelist,
so fifos can't be created at all except by tasks which have 'a'
in their whitelist (meaning they have access to all devices).
Fix the behavior by bypassing access checks to mkfifo.
Signed-off-by: Serge E. Hallyn <[email protected]>
---
security/device_cgroup.c | 3 +++
1 files changed, 3 insertions(+), 0 deletions(-)
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 5ba7870..df9d491 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -513,6 +513,9 @@ int devcgroup_inode_mknod(int mode, dev_t dev)
struct dev_cgroup *dev_cgroup;
struct dev_whitelist_item *wh;
+ if (!S_ISBLK(mode) && !S_ISCHR(mode))
+ return 0;
+
rcu_read_lock();
dev_cgroup = task_devcgroup(current);
--
1.5.4.3
CC: Andrew
Serge E. Hallyn wrote:
> The devcgroup_inode_permission() hook in the devices whitelist
> cgroup has always bypassed access checks on fifos. But the
> mknod hook did not. The devices whitelist is only about block
> and char devices, and fifos can't even be added to the whitelist,
> so fifos can't be created at all except by tasks which have 'a'
> in their whitelist (meaning they have access to all devices).
>
> Fix the behavior by bypassing access checks to mkfifo.
>
It also bypasses checks to mksock. Should backport this patch?
Reviewed-by: Li Zefan <[email protected]>
> Signed-off-by: Serge E. Hallyn <[email protected]>
> ---
> security/device_cgroup.c | 3 +++
> 1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/security/device_cgroup.c b/security/device_cgroup.c
> index 5ba7870..df9d491 100644
> --- a/security/device_cgroup.c
> +++ b/security/device_cgroup.c
> @@ -513,6 +513,9 @@ int devcgroup_inode_mknod(int mode, dev_t dev)
> struct dev_cgroup *dev_cgroup;
> struct dev_whitelist_item *wh;
>
> + if (!S_ISBLK(mode) && !S_ISCHR(mode))
> + return 0;
> +
> rcu_read_lock();
>
> dev_cgroup = task_devcgroup(current);
Quoting Li Zefan ([email protected]):
> CC: Andrew
>
> Serge E. Hallyn wrote:
> > The devcgroup_inode_permission() hook in the devices whitelist
> > cgroup has always bypassed access checks on fifos. But the
> > mknod hook did not. The devices whitelist is only about block
> > and char devices, and fifos can't even be added to the whitelist,
> > so fifos can't be created at all except by tasks which have 'a'
> > in their whitelist (meaning they have access to all devices).
> >
> > Fix the behavior by bypassing access checks to mkfifo.
> >
>
> It also bypasses checks to mksock. Should backport this patch?
Do you mean push it into -stable?
Couldn't hurt, but it's a DOS to root in a container, not a security
vulnerability, and since noone has complainted until now so at least
it's not panick-worthy.
> Reviewed-by: Li Zefan <[email protected]>
Thanks. I'll go ahead and send to Linus and -stable.
-serge
> > Signed-off-by: Serge E. Hallyn <[email protected]>
> > ---
> > security/device_cgroup.c | 3 +++
> > 1 files changed, 3 insertions(+), 0 deletions(-)
> >
> > diff --git a/security/device_cgroup.c b/security/device_cgroup.c
> > index 5ba7870..df9d491 100644
> > --- a/security/device_cgroup.c
> > +++ b/security/device_cgroup.c
> > @@ -513,6 +513,9 @@ int devcgroup_inode_mknod(int mode, dev_t dev)
> > struct dev_cgroup *dev_cgroup;
> > struct dev_whitelist_item *wh;
> >
> > + if (!S_ISBLK(mode) && !S_ISCHR(mode))
> > + return 0;
> > +
> > rcu_read_lock();
> >
> > dev_cgroup = task_devcgroup(current);