Some applications, like gdb, are able to ptrace both children or other
completely unrelated tasks.  We would like to be able to discern these two
things and to be able to allow gdb to ptrace it's children, but not to be
able to ptrace unrelated tasks for security reasons.
 
Upstream is a bit weary of this patch as it may be incomplete.  They are
not fundamentally opposed to the patch, I was just ask to see if I could
flush out any needed refinement in Fedora where we already had the
problem.  We may find that we need to emulate the YAMA non-child
registration module in order to completely deal with 'normal' ptrace on
a system.  At the moment however, this patch will at least let us get
gdb working for many users in Fedora (See fedora-devel-list for a
discussion of the current issues people are complaining about in F17
without this)
 
---
 
 security/selinux/hooks.c            |   38 +++++++++++++++++++++++++++++++++++
 security/selinux/include/classmap.h |    2 +-
 security/selinux/include/security.h |    2 ++
 security/selinux/selinuxfs.c        |    3 ++-
 security/selinux/ss/services.c      |    3 +++
 5 files changed, 46 insertions(+), 2 deletions(-)
 
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 1a4acf4..b226f26 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1805,6 +1805,39 @@ static inline u32 open_file_to_av(struct file *file)
 
 /* Hook functions begin here. */
 
+/**
+ * task_is_descendant - walk up a process family tree looking for a match
+ * @parent: the process to compare against while walking up from child
+ * @child: the process to start from while looking upwards for parent
+ *
+ * Returns 1 if child is a descendant of parent, 0 if not.
+ */
+static int task_is_descendant(struct task_struct *parent,
+			      struct task_struct *child)
+{
+	int rc = 0;
+	struct task_struct *walker = child;
+
+	if (!parent || !child)
+		return 0;
+
+	rcu_read_lock();
+	if (!thread_group_leader(parent))
+		parent = rcu_dereference(parent->group_leader);
+	while (walker->pid > 0) {
+		if (!thread_group_leader(walker))
+			walker = rcu_dereference(walker->group_leader);
+		if (walker == parent) {
+			rc = 1;
+			break;
+		}
+		walker = rcu_dereference(walker->real_parent);
+	}
+	rcu_read_unlock();
+
+	return rc;
+}
+
 static int selinux_ptrace_access_check(struct task_struct *child,
 				     unsigned int mode)
 {
@@ -1820,6 +1853,9 @@ static int selinux_ptrace_access_check(struct task_struct *child,
 		return avc_has_perm(sid, csid, SECCLASS_FILE, FILE__READ, NULL);
 	}
 
+
+	if (selinux_policycap_ptrace_child && task_is_descendant(current, child))
+		return current_has_perm(child, PROCESS__PTRACE_CHILD);
 	return current_has_perm(child, PROCESS__PTRACE);
 }
 
@@ -1831,6 +1867,8 @@ static int selinux_ptrace_traceme(struct task_struct *parent)
 	if (rc)
 		return rc;
 
+	if (selinux_policycap_ptrace_child && task_is_descendant(parent, current))
+		return task_has_perm(parent, current, PROCESS__PTRACE_CHILD);
 	return task_has_perm(parent, current, PROCESS__PTRACE);
 }
 
diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
index 39e678c..72c08b9 100644
--- a/security/selinux/include/classmap.h
+++ b/security/selinux/include/classmap.h
@@ -29,7 +29,7 @@ struct security_class_mapping secclass_map[] = {
 	    "getattr", "setexec", "setfscreate", "noatsecure", "siginh",
 	    "setrlimit", "rlimitinh", "dyntransition", "setcurrent",
 	    "execmem", "execstack", "execheap", "setkeycreate",
-	    "setsockcreate", NULL } },
+	    "setsockcreate", "ptrace_child", NULL } },
 	{ "system",
 	  { "ipc_info", "syslog_read", "syslog_mod",
 	    "syslog_console", "module_request", NULL } },
diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index dde2005..ac14b0a 100644
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -68,12 +68,14 @@ extern int selinux_enabled;
 enum {
 	POLICYDB_CAPABILITY_NETPEER,
 	POLICYDB_CAPABILITY_OPENPERM,
+	POLICYDB_CAPABILITY_PTRACE_CHILD,
 	__POLICYDB_CAPABILITY_MAX
 };
 #define POLICYDB_CAPABILITY_MAX (__POLICYDB_CAPABILITY_MAX - 1)
 
 extern int selinux_policycap_netpeer;
 extern int selinux_policycap_openperm;
+extern int selinux_policycap_ptrace_child;
 
 /*
  * type_datum properties
diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index 4e93f9e..3379765 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -44,7 +44,8 @@
 /* Policy capability filenames */
 static char *policycap_names[] = {
 	"network_peer_controls",
-	"open_perms"
+	"open_perms",
+	"ptrace_child",
 };
 
 unsigned int selinux_checkreqprot = CONFIG_SECURITY_SELINUX_CHECKREQPROT_VALUE;
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 9b7e7ed..4d12a6e 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -72,6 +72,7 @@
 
 int selinux_policycap_netpeer;
 int selinux_policycap_openperm;
+int selinux_policycap_ptrace_child;
 
 static DEFINE_RWLOCK(policy_rwlock);
 
@@ -1812,6 +1813,8 @@ static void security_load_policycaps(void)
 						  POLICYDB_CAPABILITY_NETPEER);
 	selinux_policycap_openperm = ebitmap_get_bit(&policydb.policycaps,
 						  POLICYDB_CAPABILITY_OPENPERM);
+	selinux_policycap_ptrace_child = ebitmap_get_bit(&policydb.policycaps,
+						  POLICYDB_CAPABILITY_PTRACE_CHILD);
 }
 
 static int security_preserve_bools(struct policydb *p);
 
 
 
 
_______________________________________________
kernel mailing list
kernel@lists.fedoraproject.org
https://admin.fedoraproject.org/mailman/listinfo/kernel