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@xxxxxxxxxx>
---
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
--
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