[PATCH] mount.cifs: properly prune the capabilities bounding set

...libcap-ng does this in a much easier fashion. If that's not
available, then we have to do it manually.

Signed-off-by: Jeff Layton <[email protected]>
---
 configure.ac |    3 +++
 mount.cifs.c |   37 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 39 insertions(+), 1 deletions(-)

diff --git a/configure.ac b/configure.ac
index 857b0d8..d734d62 100644
--- a/configure.ac
+++ b/configure.ac
@@ -100,6 +100,9 @@ AC_FUNC_STRNLEN
 # check for required functions
 AC_CHECK_FUNCS([alarm atexit endpwent getmntent getpass gettimeofday inet_ntop memset realpath setenv strchr strdup strerror strncasecmp strndup strpbrk strrchr strstr strtol strtoul uname], , [AC_MSG_ERROR([necessary functions(s) not found])])
 
+# check for prctl
+AC_CHECK_FUNCS([prctl])
+
 # ugly, but I'm not sure how to check for functions in a library that's not in $LIBS
 cu_saved_libs=$LIBS
 LIBS="$LIBS $KRB5_LDADD"
diff --git a/mount.cifs.c b/mount.cifs.c
index 1ff1846..712a8fe 100644
--- a/mount.cifs.c
+++ b/mount.cifs.c
@@ -47,6 +47,9 @@
 #ifdef HAVE_LIBCAP_NG
 #include <cap-ng.h>
 #else /* HAVE_LIBCAP_NG */
+#ifdef HAVE_PRCTL
+#include <sys/prctl.h>
+#endif /* HAVE_PRCTL */
 #ifdef HAVE_LIBCAP
 #include <sys/capability.h>
 #endif /* HAVE_LIBCAP */
@@ -364,14 +367,46 @@ toggle_cap_dac_override(int enable)
 	return 0;
 }
 #else /* HAVE_LIBCAP_NG */
+#ifdef HAVE_PRCTL
+static int
+prune_bounding_set(void)
+{
+	int i, rc = 0;
+	static int bounding_set_cleared;
+
+	if (bounding_set_cleared)
+		return 0;
+
+	for (i = 0; i < CAP_LAST_CAP && rc == 0; ++i)
+		rc = prctl(PR_CAPBSET_DROP, i);
+
+	if (rc != 0) {
+		fprintf(stderr, "Unable to clear capability bounding set: %d\n", rc);
+		return EX_SYSERR;
+	}
+
+	++bounding_set_cleared;
+	return 0;
+}
+#else /* HAVE_PRCTL */
+static int
+prune_bounding_set(void)
+{
+	return 0;
+}
+#endif /* HAVE_PRCTL */
 #ifdef HAVE_LIBCAP
 static int
 drop_capabilities(int parent)
 {
-	int rc = 0, ncaps;
+	int rc, ncaps;
 	cap_t caps;
 	cap_value_t cap_list[2];
 
+	rc = prune_bounding_set();
+	if (rc)
+		return rc;
+
 	caps = cap_get_proc();
 	if (caps == NULL) {
 		fprintf(stderr, "Unable to get current capability set: %s\n",
-- 
1.6.6.1