openssh/openssh-7.2p2-chroot-capabilities.patch

diff --git a/configure.ac b/configure.ac
index aeef42a..d01e67e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -4998,6 +4998,37 @@ if test -n "$conf_lastlog_location"; then
 		[Define if you want to specify the path to your lastlog file])
 fi
 
+AC_ARG_WITH(libcap-ng,
+	[  --with-libcap-ng=[auto/yes/no]  Add Libcap-ng support [default=auto]],,
+	with_libcap_ng=auto)
+
+dnl libcap-ng detection
+if test x$with_libcap_ng = xno ; then
+	have_libcap_ng=no;
+else
+	# Start by checking for header file
+	AC_CHECK_HEADER(cap-ng.h, capng_headers=yes, capng_headers=no)
+
+	# See if we have libcap-ng library
+	AC_CHECK_LIB(cap-ng, capng_clear, CAPNG_LDADD=-lcap-ng,)
+
+	# Check results are usable
+	if test x$with_libcap_ng = xyes -a x$CAPNG_LDADD = x ; then
+	AC_MSG_ERROR(libcap-ng support was requested and the library was not found)
+	fi
+	if test x$CAPNG_LDADD != x -a $capng_headers = no ; then
+	AC_MSG_ERROR(libcap-ng libraries found but headers are missing)
+	fi
+fi
+AC_MSG_CHECKING(whether to use libcap-ng)
+if test x$CAPNG_LDADD != x ; then
+	AC_DEFINE(HAVE_LIBCAP_NG,1,[libcap-ng support])
+	SSHDLIBS="$SSHDLIBS -lcap-ng"
+	AC_MSG_RESULT(yes)
+else
+	AC_MSG_RESULT(no)
+fi
+
 dnl utmp detection
 AC_MSG_CHECKING([if your system defines UTMP_FILE])
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
diff --git a/session.c b/session.c
index 6cfcba4..80d2806 100644
--- a/session.c
+++ b/session.c
@@ -96,6 +96,10 @@
 #include "monitor_wrap.h"
 #include "sftp.h"
 
+#ifdef HAVE_LIBCAP_NG
+#include <cap-ng.h>
+#endif
+
 #if defined(KRB5) && defined(USE_AFS)
 #include <kafs.h>
 #endif
@@ -1586,6 +1590,7 @@ void
 do_setusercontext(struct passwd *pw)
 {
 	char *chroot_path, *tmp;
+	int dropped_suid = -1;
 
 	platform_setusercontext(pw);
 
@@ -1619,10 +1624,25 @@ do_setusercontext(struct passwd *pw)
 			    pw->pw_uid);
 			chroot_path = percent_expand(tmp, "h", pw->pw_dir,
 			    "u", pw->pw_name, (char *)NULL);
+#ifdef HAVE_LIBCAP_NG
+			/* drop suid soon, retain SYS_CHROOT capability */
+			capng_clear(CAPNG_SELECT_BOTH);
+			capng_update(CAPNG_ADD, CAPNG_EFFECTIVE|CAPNG_PERMITTED, CAP_SYS_CHROOT);
+			if (pw->pw_uid != 0 &&
+			    (dropped_suid = capng_change_id(pw->pw_uid, pw->pw_gid, CAPNG_INIT_SUPP_GRP)) != 0)
+				logit("capng_change_id() = %d (failure): Try to drop UID later", dropped_suid);
+#endif
 #ifdef WITH_SELINUX
 			sshd_selinux_copy_context();
 #endif
 			safely_chroot(chroot_path, pw->pw_uid);
+#ifdef HAVE_LIBCAP_NG
+			/* Drop chroot capability. Already used */
+			if (dropped_suid == 0) {
+				capng_clear(CAPNG_SELECT_BOTH);
+				capng_apply(CAPNG_SELECT_BOTH);
+			}
+#endif
 			free(tmp);
 			free(chroot_path);
 			/* Make sure we don't attempt to chroot again */
@@ -1654,8 +1673,9 @@ do_setusercontext(struct passwd *pw)
 		if (!in_chroot && set_id(pw->pw_name) != 0)
 			fatal("set_id(%s) Failed", pw->pw_name);
 # endif /* USE_LIBIAF */
-		/* Permanently switch to the desired uid. */
-		permanently_set_uid(pw);
+		/* Permanently switch to the desired uid if not yet done. */
+		if (dropped_suid != 0)
+			permanently_set_uid(pw);
 #endif
 
 #ifdef WITH_SELINUX