nsenter,unshare: don't use xvfork_parent_waits_and_exits(), it SEGVs on ppc64le

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

3 files changed, 25 insertions, 2 deletions

diff --git a/libbb/xfuncs_printf.c b/libbb/xfuncs_printf.c
index 842d10cd2..d413c81e8 100644
--- a/libbb/xfuncs_printf.c
+++ b/libbb/xfuncs_printf.c
@@ -696,6 +696,14 @@ pid_t FAST_FUNC xfork(void)
 }
 #endif
 
+#if 0
+/* DO NOT DO THIS. This can't be a function.
+ * It works on some arches (x86) but fails on others (ppc64le: SEGV).
+ * The reason is: the child returns from this function
+ * and likely pops up the stack in an arch-dependent way.
+ * When child eventually exits or execs, parent "reappear"
+ * in the now-unwound stack (!) and the behavior is undefined.
+ */
 void FAST_FUNC xvfork_parent_waits_and_exits(void)
 {
 	pid_t pid;
@@ -711,6 +719,7 @@ void FAST_FUNC xvfork_parent_waits_and_exits(void)
 	}
 	/* Child continues */
 }
+#endif
 
 // Useful when we do know that pid is valid, and we just want to wait
 // for it to exit. Not existing pid is fatal. waitpid() status is not returned.
diff --git a/util-linux/nsenter.c b/util-linux/nsenter.c
index 9a250e43c..425d5175f 100644
--- a/util-linux/nsenter.c
+++ b/util-linux/nsenter.c
@@ -251,7 +251,14 @@ int nsenter_main(int argc UNUSED_PARAM, char **argv)
 	 * explicitly requested by the user not to.
 	 */
 	if (!(opts & OPT_nofork) && (opts & OPT_pid)) {
-		xvfork_parent_waits_and_exits();
+		pid_t pid = xvfork();
+		if (pid > 0) {
+			/* Parent */
+			int exit_status = wait_for_exitstatus(pid);
+			if (WIFSIGNALED(exit_status))
+				kill_myself_with_sig(WTERMSIG(exit_status));
+			return WEXITSTATUS(exit_status);
+		}
 		/* Child continues */
 	}
 
diff --git a/util-linux/unshare.c b/util-linux/unshare.c
index a9f56f388..f58cdd93e 100644
--- a/util-linux/unshare.c
+++ b/util-linux/unshare.c
@@ -333,7 +333,14 @@ int unshare_main(int argc UNUSED_PARAM, char **argv)
 	 * that'll become PID 1 in this new namespace.
 	 */
 	if (opts & OPT_fork) {
-		xvfork_parent_waits_and_exits();
+		pid_t pid = xvfork();
+		if (pid > 0) {
+			/* Parent */
+			int exit_status = wait_for_exitstatus(pid);
+			if (WIFSIGNALED(exit_status))
+				kill_myself_with_sig(WTERMSIG(exit_status));
+			return WEXITSTATUS(exit_status);
+		}
 		/* Child continues */
 	}