[PATCH 1/3] Security: Add disablenetwork interface. (v4)

[Michael Stone <michael@laptop.org>]

Daniel Bernstein has observed [1] that security-conscious userland processes
may benefit from the ability to irrevocably remove their ability to create,
bind, connect to, or send messages except in the case of previously connected
sockets or AF_UNIX filesystem sockets.

This patch provides

   * a new configuration option named CONFIG_SECURITY_DISABLENETWORK,
   * a new prctl option-pair (PR_SET_NETWORK, PR_GET_NETWORK),
   * a new prctl(PR_SET_NETWORK) flag named PR_NETWORK_OFF, and
   * a new task_struct flags field named "network"

Signed-off-by: Michael Stone <michael@laptop.org>
---
  include/linux/prctl.h         |    7 +++++
  include/linux/prctl_network.h |    7 +++++
  include/linux/sched.h         |    4 +++
  kernel/sys.c                  |   53 +++++++++++++++++++++++++++++++++++++++++
  security/Kconfig              |   11 ++++++++
  5 files changed, 82 insertions(+), 0 deletions(-)
  create mode 100644 include/linux/prctl_network.h

diff --git a/include/linux/prctl.h b/include/linux/prctl.h
index a3baeb2..4eb4110 100644
--- a/include/linux/prctl.h
+++ b/include/linux/prctl.h
@@ -102,4 +102,11 @@
  
  #define PR_MCE_KILL_GET 34
  
+/* 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
+
  #endif /* _LINUX_PRCTL_H */
diff --git a/include/linux/prctl_network.h b/include/linux/prctl_network.h
new file mode 100644
index 0000000..d18f8cb
--- /dev/null
+++ b/include/linux/prctl_network.h
@@ -0,0 +1,7 @@
+#ifndef _LINUX_PRCTL_NETWORK_H
+#define _LINUX_PRCTL_NETWORK_H
+
+extern long prctl_get_network(unsigned long*);
+extern long prctl_set_network(unsigned long*);
+
+#endif /* _LINUX_PRCTL_NETWORK_H */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f2f842d..6fcaef8 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1403,6 +1403,10 @@ struct task_struct {
  #endif
  	seccomp_t seccomp;
  
+#ifdef CONFIG_SECURITY_DISABLENETWORK
+  unsigned long network;
+#endif
+
  /* Thread group tracking */
     	u32 parent_exec_id;
     	u32 self_exec_id;
diff --git a/kernel/sys.c b/kernel/sys.c
index 26a6b73..b48f021 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -35,6 +35,7 @@
  #include <linux/cpu.h>
  #include <linux/ptrace.h>
  #include <linux/fs_struct.h>
+#include <linux/prctl_network.h>
  
  #include <linux/compat.h>
  #include <linux/syscalls.h>
@@ -1578,6 +1579,12 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
  			else
  				error = PR_MCE_KILL_DEFAULT;
  			break;
+		case PR_SET_NETWORK:
+			error = prctl_set_network((unsigned long*)arg2);
+			break;
+		case PR_GET_NETWORK:
+			error = prctl_get_network((unsigned long*)arg2);
+			break;
  		default:
  			error = -EINVAL;
  			break;
@@ -1585,6 +1592,52 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
  	return error;
  }
  
+#ifdef CONFIG_SECURITY_DISABLENETWORK
+
+long prctl_get_network(unsigned long* user)
+{
+	return put_user(current->network, user);
+}
+
+long prctl_set_network(unsigned long* user)
+{
+	unsigned long network_flags;
+	long ret;
+
+	ret = -EFAULT;
+	if (copy_from_user(&network_flags, user, sizeof(network_flags)))
+		goto out;
+
+	ret = -EINVAL;
+	if (network_flags & ~PR_NETWORK_ALL_FLAGS)
+		goto out;
+
+	/* only dropping access is permitted */
+	ret = -EPERM;
+        if (current->network & ~network_flags)
+		goto out;
+
+	current->network = network_flags;
+	ret = 0;
+
+out:
+	return ret;
+}
+
+#else
+
+long prctl_get_network(unsigned long* user)
+{
+	return -ENOSYS;
+}
+
+long prctl_set_network(unsigned long* user)
+{
+	return -ENOSYS;
+}
+
+#endif /* ! CONFIG_SECURITY_DISABLENETWORK */
+
  SYSCALL_DEFINE3(getcpu, unsigned __user *, cpup, unsigned __user *, nodep,
  		struct getcpu_cache __user *, unused)
  {
diff --git a/security/Kconfig b/security/Kconfig
index 226b955..afd7f76 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -137,6 +137,17 @@ config LSM_MMAP_MIN_ADDR
  	  this low address space will need the permission specific to the
  	  systems running LSM.
  
+config SECURITY_DISABLENETWORK
+	bool "Socket and networking discretionary access control"
+	depends on SECURITY_NETWORK
+	help
+    This enables processes to drop networking privileges via
+    prctl(PR_SET_NETWORK, PR_NETWORK_OFF).
+
+    See Documentation/disablenetwork.txt for more information.
+
+	  If you are unsure how to answer this question, answer N.
+
  source security/selinux/Kconfig
  source security/smack/Kconfig
  source security/tomoyo/Kconfig
-- 
1.6.6.rc2