nsenter,unshare: share common code; fix a bug of not closing all fds

function                                             old     new   delta
xvfork_parent_waits_and_exits                          -      64     +64
exec_prog_or_SHELL                                     -      39     +39
unshare_main                                         873     810     -63
nsenter_main                                         663     596     -67
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 0/2 up/down: 106/-130)          Total: -27 bytes

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

5 files changed, 38 insertions, 35 deletions

diff --git a/include/libbb.h b/include/libbb.h
index 5b4280e34..64e61cd26 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -992,9 +992,10 @@ int BB_EXECVP(const char *file, char *const argv[]) FAST_FUNC;
 #define BB_EXECVP(prog,cmd)     execvp(prog,cmd)
 #define BB_EXECLP(prog,cmd,...) execlp(prog,cmd,__VA_ARGS__)
 #endif
-int BB_EXECVP_or_die(char **argv) NORETURN FAST_FUNC;
+void BB_EXECVP_or_die(char **argv) NORETURN FAST_FUNC;
+void exec_prog_or_SHELL(char **argv) NORETURN FAST_FUNC;
 
-/* xvfork() can't be a _function_, return after vfork mangles stack
+/* xvfork() can't be a _function_, return after vfork in child mangles stack
  * in the parent. It must be a macro. */
 #define xvfork() \
 ({ \
@@ -1006,6 +1007,7 @@ int BB_EXECVP_or_die(char **argv) NORETURN FAST_FUNC;
 #if BB_MMU
 pid_t xfork(void) FAST_FUNC;
 #endif
+void xvfork_parent_waits_and_exits(void) FAST_FUNC;
 
 /* NOMMU friendy fork+exec: */
 pid_t spawn(char **argv) FAST_FUNC;
diff --git a/libbb/executable.c b/libbb/executable.c
index 85ecc3e6c..05e70312f 100644
--- a/libbb/executable.c
+++ b/libbb/executable.c
@@ -83,10 +83,19 @@ int FAST_FUNC BB_EXECVP(const char *file, char *const argv[])
 }
 #endif
 
-int FAST_FUNC BB_EXECVP_or_die(char **argv)
+void FAST_FUNC BB_EXECVP_or_die(char **argv)
 {
         BB_EXECVP(argv[0], argv);
         /* SUSv3-mandated exit codes */
         xfunc_error_retval = (errno == ENOENT) ? 127 : 126;
         bb_perror_msg_and_die("can't execute '%s'", argv[0]);
 }
+
+/* Typical idiom for applets which exec *optional* PROG [ARGS] */
+void FAST_FUNC exec_prog_or_SHELL(char **argv)
+{
+        if (argv[0]) {
+                BB_EXECVP_or_die(argv);
+        }
+        run_shell(getenv("SHELL"), /*login:*/ 1, NULL, NULL);
+}
diff --git a/libbb/xfuncs_printf.c b/libbb/xfuncs_printf.c
index 4aa1b5ce2..e9222f690 100644
--- a/libbb/xfuncs_printf.c
+++ b/libbb/xfuncs_printf.c
@@ -659,3 +659,19 @@ pid_t FAST_FUNC xfork(void)
         return pid;
 }
 #endif
+
+void FAST_FUNC xvfork_parent_waits_and_exits(void)
+{
+        pid_t pid;
+
+        fflush_all();
+        pid = xvfork();
+        if (pid > 0) {
+                /* Parent */
+                int exit_status = wait_for_exitstatus(pid);
+                if (WIFSIGNALED(exit_status))
+                        kill_myself_with_sig(WTERMSIG(exit_status));
+                _exit(WEXITSTATUS(exit_status));
+        }
+        /* Child continues */
+}
diff --git a/util-linux/nsenter.c b/util-linux/nsenter.c
index 9c1dabaa8..0dad595cd 100644
--- a/util-linux/nsenter.c
+++ b/util-linux/nsenter.c
@@ -230,7 +230,7 @@ int nsenter_main(int argc UNUSED_PARAM, char **argv)
                                 ns->ns_nsfile8 + 3 /* skip over "ns/" */
                         );
                 }
-                /*close(ns_ctx->fd);*/
+                close(ns_ctx->fd); /* should close fds, to not confuse exec'ed PROG */
                 /*ns_ctx->fd = -1;*/
         }
 
@@ -244,13 +244,13 @@ int nsenter_main(int argc UNUSED_PARAM, char **argv)
                 }
                 xfchdir(root_fd);
                 xchroot(".");
-                /*close(root_fd);*/
+                close(root_fd);
                 /*root_fd = -1;*/
         }
 
         if (wd_fd >= 0) {
                 xfchdir(wd_fd);
-                /*close(wd_fd);*/
+                close(wd_fd);
                 /*wd_fd = -1;*/
         }
 
@@ -259,14 +259,7 @@ int nsenter_main(int argc UNUSED_PARAM, char **argv)
          * explicitly requested by the user not to.
          */
         if (!(opts & OPT_nofork) && (opts & OPT_pid)) {
-                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);
-                }
+                xvfork_parent_waits_and_exits();
                 /* Child continues */
         }
 
@@ -278,9 +271,5 @@ int nsenter_main(int argc UNUSED_PARAM, char **argv)
         if (opts & OPT_setuid)
                 xsetuid(uid);
 
-        if (*argv) {
-                BB_EXECVP_or_die(argv);
-        }
-
-        run_shell(getenv("SHELL"), /*login:*/ 1, NULL, NULL);
+        exec_prog_or_SHELL(argv);
 }
diff --git a/util-linux/unshare.c b/util-linux/unshare.c
index 2a5bea5a6..95a7cb647 100644
--- a/util-linux/unshare.c
+++ b/util-linux/unshare.c
@@ -281,7 +281,7 @@ int unshare_main(int argc UNUSED_PARAM, char **argv)
 
         if (fdp.wr >= 0) {
                 close(fdp.wr); /* Release child */
-                /*close(fdp.rd);*/
+                close(fdp.rd); /* should close fd, to not confuse exec'ed PROG */
         }
 
         if (need_mount) {
@@ -307,14 +307,7 @@ int unshare_main(int argc UNUSED_PARAM, char **argv)
          * that'll become PID 1 in this new namespace.
          */
         if (opts & OPT_fork) {
-                pid_t pid = xfork();
-                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);
-                }
+                xvfork_parent_waits_and_exits();
                 /* Child continues */
         }
 
@@ -354,11 +347,5 @@ int unshare_main(int argc UNUSED_PARAM, char **argv)
                 mount_or_die("proc", proc_mnt_target, "proc", MS_NOSUID | MS_NOEXEC | MS_NODEV);
         }
 
-        if (argv[0]) {
-                BB_EXECVP_or_die(argv);
-        }
-        /* unshare from util-linux 2.27.1, despite not documenting it,
-         * runs a login shell (argv0="-sh") if no PROG is given
-         */
-        run_shell(getenv("SHELL"), /*login:*/ 1, NULL, NULL);
+        exec_prog_or_SHELL(argv);
 }