From 805334b26c7e6e83557234f2008497c72176a6cd Mon Sep 17 00:00:00 2001 From: Adhemerval Zanella Date: Wed, 19 Sep 2018 12:14:34 -0700 Subject: posix: Clear close-on-exec for posix_spawn adddup2 (BZ#23640) 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. [BZ #23640] * 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 --- sysdeps/unix/sysv/linux/spawni.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) (limited to 'sysdeps/unix/sysv') diff --git a/sysdeps/unix/sysv/linux/spawni.c b/sysdeps/unix/sysv/linux/spawni.c index c497869a74..353bcf5b33 100644 --- a/sysdeps/unix/sysv/linux/spawni.c +++ b/sysdeps/unix/sysv/linux/spawni.c @@ -253,9 +253,21 @@ __spawni_child (void *arguments) break; case spawn_do_dup2: - if (__dup2 (action->action.dup2_action.fd, - action->action.dup2_action.newfd) - != 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) + { + 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; + } + else if (__dup2 (action->action.dup2_action.fd, + action->action.dup2_action.newfd) + != action->action.dup2_action.newfd) goto fail; break; -- cgit 1.4.1