Re: disablenetwork (v5): Require CAP_SETPCAP to enable disablenetwork.

[Andrew G. Morgan]

On Fri, Jan 15, 2010 at 12:13 AM, Michael Stone <michael@xxxxxxxxxx> wrote:
> We implement this check by allocating a new flag bit in task_struct->network
> and by propagating its semantics throughout the disablenetwork facility.
>
> Signed-off-by: Michael Stone <michael@xxxxxxxxxx>
> ---
>  include/linux/prctl.h     |    8 +++++---
>  kernel/sys.c              |   14 +++++++++++++-
>  security/disablenetwork.c |   15 ++++++++-------
>  3 files changed, 26 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/prctl.h b/include/linux/prctl.h
> index 4eb4110..4fdb417 100644
> --- a/include/linux/prctl.h
> +++ b/include/linux/prctl.h
> @@ -105,8 +105,10 @@
>  /* Get/set process disable-network flags */
>  #define PR_SET_NETWORK        35
>  #define PR_GET_NETWORK        36
> -# define PR_NETWORK_ON        0
> -# define PR_NETWORK_OFF       1
> -# define PR_NETWORK_ALL_FLAGS 1
> +# define PR_NETWORK_ON         0
> +# define PR_NETWORK_ENABLE_DN  1
> +# define PR_NETWORK_OFF        2
> +# define PR_NETWORK_ALL_FLAGS  3
> +# define PR_NETWORK_DN_FLAGS   3
>
>  #endif /* _LINUX_PRCTL_H */
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 1fadf10..4c7ef83 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -1608,7 +1608,19 @@ long prctl_set_network(unsigned long network_flags)
>        if (current->network & ~network_flags)
>                return -EPERM;
>
> -       current->network = network_flags;
> +       /* Only the superuser may permit a process to enable disablenetwork. */
> +       if (!(current->network & PR_NETWORK_ENABLE_DN) &&
> +               network_flags & PR_NETWORK_ENABLE_DN &&
> +               !capable(CAP_SETPCAP))

Please use CAP_NET_ADMIN for this feature (and add the corresponding
comment in include/linux/capabilities.h).

Thanks

Andrew

> +               return -EPERM;
> +
> +       /* Only dn-enabled processes may activate disablenetwork. */
> +       if (!(current->network & PR_NETWORK_OFF) &&
> +               network_flags & PR_NETWORK_OFF &&
> +               !(current->network & PR_NETWORK_ENABLE_DN))
> +               return -EPERM;
> +
> +       current->network |= network_flags;
>        return 0;
>  }
>
> diff --git a/security/disablenetwork.c b/security/disablenetwork.c
> index 27b88d7..02c0150 100644
> --- a/security/disablenetwork.c
> +++ b/security/disablenetwork.c
> @@ -19,10 +19,11 @@
>  #include <net/sock.h>
>  #include <linux/socket.h>
>  #include <linux/disablenetwork.h>
> +#include <linux/prctl.h>
>
> -static inline int maybe_allow(void)
> +static inline int maybe_allow(unsigned long network_flags)
>  {
> -       if (current->network)
> +       if ((network_flags & PR_NETWORK_DN_FLAGS) == PR_NETWORK_DN_FLAGS)
>                return -EPERM;
>        return 0;
>  }
> @@ -32,7 +33,7 @@ int disablenetwork_security_socket_create(int family, int type,
>  {
>        if (family == AF_UNIX)
>                return 0;
> -       return maybe_allow();
> +       return maybe_allow(current->network);
>  }
>
>  int disablenetwork_security_socket_bind(struct socket * sock,
> @@ -41,7 +42,7 @@ int disablenetwork_security_socket_bind(struct socket * sock,
>  {
>        if (address->sa_family == AF_UNIX)
>                return 0;
> -       return maybe_allow();
> +       return maybe_allow(current->network);
>  }
>
>  int disablenetwork_security_socket_connect(struct socket * sock,
> @@ -50,7 +51,7 @@ int disablenetwork_security_socket_connect(struct socket * sock,
>  {
>        if (address->sa_family == AF_UNIX)
>                return 0;
> -       return maybe_allow();
> +       return maybe_allow(current->network);
>  }
>
>  int disablenetwork_security_socket_sendmsg(struct socket * sock,
> @@ -59,14 +60,14 @@ int disablenetwork_security_socket_sendmsg(struct socket * sock,
>        /* permit sockets which are PF_UNIX or connected; check others. */
>        if (sock->sk->sk_family == PF_UNIX || msg->msg_name == NULL)
>                return 0;
> -       return maybe_allow();
> +       return maybe_allow(current->network);
>  }
>
>  int disablenetwork_security_ptrace_access_check(struct task_struct *child,
>                                                  unsigned int mode)
>  {
>        /* does current have networking restrictions not shared by child? */
> -       if (current->network & ~child->network)
> +       if (maybe_allow(current->network) && !maybe_allow(child->network))
>                return -EPERM;
>        return 0;
>  }
> --
> 1.6.6.rc2
>
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