From e2446fda6e7cdb1b9462162b81b0e50fd6efaf56 Mon Sep 17 00:00:00 2001
From: Chuck Lever <chuck.lever@oracle.com>
Date: Thu, 14 Jan 2010 12:24:34 -0500
Subject: [PATCH] libnsm.a: retain CAP_NET_BIND when dropping privileges

I'm about to switch the order of listener creation and dropping root
privileges.  rpc.statd will drop privileges first, then create its
listeners.  The reason for the new ordering is explained in a
subsequent patch.

However, for non-TI-RPC builds, rpc_init() needs to use a privileged
port to do pmap registrations.  For both TI-RPC and non-TI-RPC builds,
CAP_NET_BIND is required in case the admin requests a privileged
listener port on the statd command line.

So that these requirements are met, nsm_drop_privileges() will now
retain CAP_NET_BIND while dropping root.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 aclocal/libcap.m4       | 15 +++++++++++++++
 configure.ac            |  3 +++
 support/nsm/file.c      | 41 ++++++++++++++++++++++++++++++++++++++++-
 utils/statd/Makefile.am |  4 ++--
 4 files changed, 60 insertions(+), 3 deletions(-)
 create mode 100644 aclocal/libcap.m4

diff --git a/aclocal/libcap.m4 b/aclocal/libcap.m4
new file mode 100644
index 0000000..eabe507
--- /dev/null
+++ b/aclocal/libcap.m4
@@ -0,0 +1,15 @@
+dnl Checks for libcap.so
+dnl
+AC_DEFUN([AC_LIBCAP], [
+
+  dnl look for prctl
+  AC_CHECK_FUNC([prctl], , )
+
+  dnl look for the library; do not add to LIBS if found
+  AC_CHECK_LIB([cap], [cap_get_proc], [LIBCAP=-lcap], ,)
+  AC_SUBST(LIBCAP)
+
+  AC_CHECK_HEADERS([sys/capability.h], ,
+                   [AC_MSG_ERROR([libcap headers not found.])])
+
+])dnl
diff --git a/configure.ac b/configure.ac
index ea6f4d9..c77c5ba 100644
--- a/configure.ac
+++ b/configure.ac
@@ -166,6 +166,9 @@ fi
 dnl Check for TI-RPC library and headers
 AC_LIBTIRPC
 
+dnl Check for -lcap
+AC_LIBCAP
+
 # Check whether user wants TCP wrappers support
 AC_TCP_WRAPPERS
 
diff --git a/support/nsm/file.c b/support/nsm/file.c
index 8796705..d469219 100644
--- a/support/nsm/file.c
+++ b/support/nsm/file.c
@@ -67,6 +67,8 @@
 #endif
 
 #include <sys/types.h>
+#include <sys/capability.h>
+#include <sys/prctl.h>
 #include <sys/stat.h>
 
 #include <ctype.h>
@@ -335,6 +337,34 @@ nsm_is_default_parentdir(void)
 	return strcmp(nsm_base_dirname, NSM_DEFAULT_STATEDIR) == 0;
 }
 
+/*
+ * Clear all capabilities but CAP_NET_BIND_SERVICE.  This permits
+ * callers to acquire privileged source ports, but all other root
+ * capabilities are disallowed.
+ *
+ * Returns true if successful, or false if some error occurred.
+ */
+static _Bool
+nsm_clear_capabilities(void)
+{
+	cap_t caps;
+
+	caps = cap_from_text("cap_net_bind_service=ep");
+	if (caps == NULL) {
+		xlog(L_ERROR, "Failed to allocate capability: %m");
+		return false;
+	}
+
+	if (cap_set_proc(caps) == -1) {
+		xlog(L_ERROR, "Failed to set capability flags: %m");
+		(void)cap_free(caps);
+		return false;
+	}
+
+	(void)cap_free(caps);
+	return true;
+}
+
 /**
  * nsm_drop_privileges - drop root privileges
  * @pidfd: file descriptor of a pid file
@@ -382,6 +412,14 @@ nsm_drop_privileges(const int pidfd)
 		if (fchown(pidfd, st.st_uid, st.st_gid) == -1)
 			xlog_warn("Failed to change owner of pidfile: %m");
 
+	/*
+	 * Don't clear capabilities when dropping root.
+	 */
+        if (prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0) == -1) {
+                xlog(L_ERROR, "prctl(PR_SET_KEEPCAPS) failed: %m");
+		return 0;
+	}
+
 	if (setgroups(0, NULL) == -1) {
 		xlog(L_ERROR, "Failed to drop supplementary groups: %m");
 		return false;
@@ -399,7 +437,8 @@ nsm_drop_privileges(const int pidfd)
 	}
 
 	xlog(D_CALL, "Effective UID, GID: %u, %u", st.st_uid, st.st_gid);
-	return true;
+
+	return nsm_clear_capabilities();
 }
 
 /**
diff --git a/utils/statd/Makefile.am b/utils/statd/Makefile.am
index a94c012..1744791 100644
--- a/utils/statd/Makefile.am
+++ b/utils/statd/Makefile.am
@@ -15,10 +15,10 @@ BUILT_SOURCES = $(GENFILES)
 statd_LDADD = ../../support/nsm/libnsm.a \
 	      ../../support/nfs/libnfs.a \
 	      ../../support/misc/libmisc.a \
-	      $(LIBWRAP) $(LIBNSL)
+	      $(LIBWRAP) $(LIBNSL) $(LIBCAP)
 sm_notify_LDADD = ../../support/nsm/libnsm.a \
 		  ../../support/nfs/libnfs.a \
-		  $(LIBNSL)
+		  $(LIBNSL) $(LIBCAP)
 
 EXTRA_DIST = sim_sm_inter.x $(man8_MANS) COPYRIGHT simulate.c
 
-- 
2.39.5