[PATCH 2/2] posix: Clear close-on-exec for posix_spawn adddup2 (BZ#23640)

[adhemerval dot zanella at linaro dot org]

From: Adhemerval Zanella <adhemerval.zanella@linaro.org>

Austin Group issue #411 [1] proposes that posix_spawn file action
posix_spawn_file_actions_adddup2 resets the close-on-exec when
source and destination refer to same file descriptor.

It solves the issue on multi-thread applications which uses
close-on-exec as default, and want to hand-chose specifically
file descriptor to purposefully inherited into a child process.
Current approach to achieve this scenario is to use two adddup2 file
actions and a temporary file description which do not conflict with
any other, coupled with a close file action to avoid leaking the
temporary file descriptor.  This approach, besides being complex,
may fail with EMFILE/ENFILE file descriptor exaustion.

This can be more easily accomplished with an in-place removal of
FD_CLOEXEC.  Although the resulting adddup2 semantic is slight
different than dup2 (equal file descriptors should be handled as
no-op), the proposed possible solution are either more complex
(fcntl action which a limited set of operations) or results in
unrequired operations (dup3 which also returns EINVAL for same
file descriptor).

Checked on aarch64-linux-gnu.

	* posix/tst-spawn.c (do_prepare, handle_restart, do_test): Add
	posix_spawn_file_actions_adddup2 test to check O_CLOCEXEC reset.
	* sysdeps/unix/sysv/linux/spawni.c (__spawni_child): Add
	close-on-exec reset for adddup2 file action.
	* sysdeps/posix/spawni.c (__spawni_child): Likewise.

[1] http://austingroupbugs.net/view.php?id=411
---
 ChangeLog                        |  6 ++++
 posix/tst-spawn.c                | 47 +++++++++++++++++++++++++-------
 sysdeps/posix/spawni.c           | 21 ++++++++++++--
 sysdeps/unix/sysv/linux/spawni.c | 21 ++++++++++++--
 4 files changed, 79 insertions(+), 16 deletions(-)

diff --git a/posix/tst-spawn.c b/posix/tst-spawn.c
index 638ba1ba55..2354417020 100644
--- a/posix/tst-spawn.c
+++ b/posix/tst-spawn.c
@@ -40,17 +40,19 @@ static int restart;
 static char *name1;
 static char *name2;
 static char *name3;
+static char *name5;
 
 /* Descriptors for the temporary files.  */
 static int temp_fd1 = -1;
 static int temp_fd2 = -1;
 static int temp_fd3 = -1;
+static int temp_fd5 = -1;
 
 /* The contents of our files.  */
 static const char fd1string[] = "This file should get closed";
 static const char fd2string[] = "This file should stay opened";
 static const char fd3string[] = "This file will be opened";
-
+static const char fd5string[] = "This file should stay opened (O_CLOEXEC)";
 
 /* We have a preparation function.  */
 static void
@@ -63,24 +65,31 @@ do_prepare (int argc, char *argv[])
   TEST_VERIFY_EXIT ((temp_fd1 = create_temp_file ("spawn", &name1)) != -1);
   TEST_VERIFY_EXIT ((temp_fd2 = create_temp_file ("spawn", &name2)) != -1);
   TEST_VERIFY_EXIT ((temp_fd3 = create_temp_file ("spawn", &name3)) != -1);
+  TEST_VERIFY_EXIT ((temp_fd5 = create_temp_file ("spawn", &name5)) != -1);
+
+  int flags;
+  TEST_VERIFY_EXIT ((flags = fcntl (temp_fd5, F_GETFD, &flags)) != -1);
+  TEST_VERIFY_EXIT (fcntl (temp_fd5, F_SETFD, flags | FD_CLOEXEC) == 0);
 }
 #define PREPARE do_prepare
 
 static int
 handle_restart (const char *fd1s, const char *fd2s, const char *fd3s,
-		const char *fd4s, const char *name)
+		const char *fd4s, const char *name, const char *fd5s)
 {
   char buf[100];
   int fd1;
   int fd2;
   int fd3;
   int fd4;
+  int fd5;
 
   /* First get the descriptors.  */
   fd1 = atol (fd1s);
   fd2 = atol (fd2s);
   fd3 = atol (fd3s);
   fd4 = atol (fd4s);
+  fd5 = atol (fd5s);
 
   /* Sanity check.  */
   TEST_VERIFY_EXIT (fd1 != fd2);
@@ -89,6 +98,7 @@ handle_restart (const char *fd1s, const char *fd2s, const char *fd3s,
   TEST_VERIFY_EXIT (fd2 != fd3);
   TEST_VERIFY_EXIT (fd2 != fd4);
   TEST_VERIFY_EXIT (fd3 != fd4);
+  TEST_VERIFY_EXIT (fd4 != fd5);
 
   /* First the easy part: read from the file descriptor which is
      supposed to be open.  */
@@ -116,6 +126,10 @@ handle_restart (const char *fd1s, const char *fd2s, const char *fd3s,
   TEST_VERIFY_EXIT (read (fd1, buf, sizeof buf) == strlen (fd1string));
   TEST_VERIFY_EXIT (memcmp (fd1string, buf, strlen (fd1string)) == 0);
 
+  TEST_VERIFY_EXIT (lseek (fd5, 0, SEEK_SET) == 0);
+  TEST_VERIFY_EXIT (read (fd5, buf, sizeof buf) == strlen (fd5string));
+  TEST_VERIFY_EXIT (memcmp (fd5string, buf, strlen (fd5string)) == 0);
+
   return 0;
 }
 
@@ -131,6 +145,7 @@ do_test (int argc, char *argv[])
   char fd2name[18];
   char fd3name[18];
   char fd4name[18];
+  char fd5name[18];
   char *name3_copy;
   char *spargv[12];
   int i;
@@ -141,21 +156,24 @@ do_test (int argc, char *argv[])
        + "--library-path"	optional
        + the library path	optional
        + the application name
-     - five parameters left if called through re-execution
+     - six parameters left if called through re-execution
        + file descriptor number which is supposed to be closed
        + the open file descriptor
        + the newly opened file descriptor
-       + thhe duped second descriptor
+       + the duped second descriptor
        + the name of the closed descriptor
+       + the duped fourth dile descriptor which O_CLOEXEC should be
+	 remove by adddup2.
   */
-  if (argc != (restart ? 6 : 2) && argc != (restart ? 6 : 5))
+  if (argc != (restart ? 7 : 2) && argc != (restart ? 7 : 5))
     FAIL_EXIT1 ("wrong number of arguments (%d)", argc);
 
   if (restart)
-    return handle_restart (argv[1], argv[2], argv[3], argv[4], argv[5]);
+    return handle_restart (argv[1], argv[2], argv[3], argv[4], argv[5],
+			   argv[6]);
 
-  /* Prepare the test.  We are creating two files: one which file descriptor
-     will be marked with FD_CLOEXEC, another which is not.  */
+  /* Prepare the test.  We are creating four files: two which file descriptor
+     will be marked with FD_CLOEXEC, another which is not  */
 
   /* Write something in the files.  */
   TEST_VERIFY_EXIT (write (temp_fd1, fd1string, strlen (fd1string))
@@ -164,6 +182,8 @@ do_test (int argc, char *argv[])
 		    == strlen (fd2string));
   TEST_VERIFY_EXIT (write (temp_fd3, fd3string, strlen (fd3string))
 		    == strlen (fd3string));
+  TEST_VERIFY_EXIT (write (temp_fd5, fd5string, strlen (fd5string))
+		    == strlen (fd5string));
 
   /* Close the third file.  It'll be opened by `spawn'.  */
   close (temp_fd3);
@@ -183,17 +203,23 @@ do_test (int argc, char *argv[])
   memset (name3_copy, 'X', strlen (name3_copy));
 
   /* We dup the second descriptor.  */
-  fd4 = MAX (2, MAX (temp_fd1, MAX (temp_fd2, temp_fd3))) + 1;
+  fd4 = MAX (2, MAX (temp_fd1, MAX (temp_fd2, MAX (temp_fd3, temp_fd5)))) + 1;
   TEST_VERIFY_EXIT (posix_spawn_file_actions_adddup2 (&actions, temp_fd2,
 						      fd4) == 0);
 
+  /* We clear the O_CLOEXEC on fourth descriptor, so it should be
+     stay open on child.  */
+  TEST_VERIFY_EXIT (posix_spawn_file_actions_adddup2 (&actions, temp_fd5,
+						      temp_fd5) == 0);
+
   /* Now spawn the process.  */
   snprintf (fd1name, sizeof fd1name, "%d", temp_fd1);
   snprintf (fd2name, sizeof fd2name, "%d", temp_fd2);
   snprintf (fd3name, sizeof fd3name, "%d", temp_fd3);
   snprintf (fd4name, sizeof fd4name, "%d", fd4);
+  snprintf (fd5name, sizeof fd5name, "%d", temp_fd5);
 
-  for (i = 0; i < (argc == (restart ? 6 : 5) ? 4 : 1); i++)
+  for (i = 0; i < (argc == (restart ? 7 : 5) ? 4 : 1); i++)
     spargv[i] = argv[i + 1];
   spargv[i++] = (char *) "--direct";
   spargv[i++] = (char *) "--restart";
@@ -202,6 +228,7 @@ do_test (int argc, char *argv[])
   spargv[i++] = fd3name;
   spargv[i++] = fd4name;
   spargv[i++] = name1;
+  spargv[i++] = fd5name;
   spargv[i] = NULL;
 
   TEST_VERIFY_EXIT (posix_spawn (&pid, argv[1], &actions, NULL, spargv,
diff --git a/sysdeps/posix/spawni.c b/sysdeps/posix/spawni.c
index b138ab4393..d322db5c19 100644
--- a/sysdeps/posix/spawni.c
+++ b/sysdeps/posix/spawni.c
@@ -204,10 +204,25 @@ __spawni_child (void *arguments)
 	      break;
 
 	    case spawn_do_dup2:
-	      if (__dup2 (action->action.dup2_action.fd,
-			  action->action.dup2_action.newfd)
+	      /* Austin Group issue #411 requires adddup2 action with source
+		 and destination being equal to remove close-on-exec flag.  */
+	      if (action->action.dup2_action.fd
 		  != action->action.dup2_action.newfd)
-		goto fail;
+		{
+		  if (__dup2 (action->action.dup2_action.fd,
+			     action->action.dup2_action.newfd)
+		      != action->action.dup2_action.newfd)
+		    goto fail;
+		}
+	      else
+		{
+		  int fd = action->action.dup2_action.newfd;
+		  int flags = __fcntl (fd, F_GETFD, 0);
+		  if (flags == -1)
+		    goto fail;
+		  if (__fcntl (fd, F_SETFD, flags & ~FD_CLOEXEC) == -1)
+		    goto fail;
+		}
 	      break;
 	    }
 	}
diff --git a/sysdeps/unix/sysv/linux/spawni.c b/sysdeps/unix/sysv/linux/spawni.c
index 85239cedbf..b2304ffe60 100644
--- a/sysdeps/unix/sysv/linux/spawni.c
+++ b/sysdeps/unix/sysv/linux/spawni.c
@@ -253,10 +253,25 @@ __spawni_child (void *arguments)
 	      break;
 
 	    case spawn_do_dup2:
-	      if (__dup2 (action->action.dup2_action.fd,
-			  action->action.dup2_action.newfd)
+	      /* Austin Group issue #411 requires adddup2 action with source
+		 and destination being equal to remove close-on-exec flag.  */
+	      if (action->action.dup2_action.fd
 		  != action->action.dup2_action.newfd)
-		goto fail;
+		{
+		  if (__dup2 (action->action.dup2_action.fd,
+			     action->action.dup2_action.newfd)
+		      != action->action.dup2_action.newfd)
+		    goto fail;
+		}
+	      else
+		{
+		  int fd = action->action.dup2_action.newfd;
+		  int flags = __fcntl (fd, F_GETFD, 0);
+		  if (flags == -1)
+		    goto fail;
+		  if (__fcntl (fd, F_SETFD, flags & ~FD_CLOEXEC) == -1)
+		    goto fail;
+		}
 	      break;
 	    }
 	}
-- 
2.17.1