svn commit: r350464 - in head/sys: compat/cloudabi kern

[Kyle Evans]

Author: kevans
Date: Wed Jul 31 15:16:51 2019
New Revision: 350464
URL: https://svnweb.freebsd.org/changeset/base/350464

Log:
  kern_shm_open: push O_CLOEXEC into caller control
  
  The motivation for this change is to allow wrappers around shm to be written
  that don't set CLOEXEC. kern_shm_open currently accepts O_CLOEXEC but sets
  it unconditionally. kern_shm_open is used by the shm_open(2) syscall, which
  is mandated by POSIX to set CLOEXEC, and CloudABI's sys_fd_create1().
  Presumably O_CLOEXEC is intended in the latter caller, but it's unclear from
  the context.
  
  sys_shm_open() now unconditionally sets O_CLOEXEC to meet POSIX
  requirements, and a comment has been dropped in to kern_fd_open() to explain
  the situation and add a pointer to where O_CLOEXEC setting is maintained for
  shm_open(2) correctness. CloudABI's sys_fd_create1() also unconditionally
  sets O_CLOEXEC to match previous behavior.
  
  This also has the side-effect of making flags correctly reflect the
  O_CLOEXEC status on this fd for the rest of kern_shm_open(), but a
  glance-over leads me to believe that it didn't really matter.
  
  Reviewed by:	kib, markj
  MFC after:	1 week
  Differential Revision:	https://reviews.freebsd.org/D21119

Modified:
  head/sys/compat/cloudabi/cloudabi_fd.c
  head/sys/kern/uipc_shm.c

Modified: head/sys/compat/cloudabi/cloudabi_fd.c
==============================================================================
--- head/sys/compat/cloudabi/cloudabi_fd.c	Wed Jul 31 05:38:39 2019	(r350463)
+++ head/sys/compat/cloudabi/cloudabi_fd.c	Wed Jul 31 15:16:51 2019	(r350464)
@@ -94,7 +94,8 @@ cloudabi_sys_fd_create1(struct thread *td,
 	case CLOUDABI_FILETYPE_SHARED_MEMORY:
 		cap_rights_init(&fcaps.fc_rights, CAP_FSTAT, CAP_FTRUNCATE,
 		    CAP_MMAP_RWX);
-		return (kern_shm_open(td, SHM_ANON, O_RDWR, 0, &fcaps));
+		return (kern_shm_open(td, SHM_ANON, O_RDWR | O_CLOEXEC, 0,
+		    &fcaps));
 	default:
 		return (EINVAL);
 	}

Modified: head/sys/kern/uipc_shm.c
==============================================================================
--- head/sys/kern/uipc_shm.c	Wed Jul 31 05:38:39 2019	(r350463)
+++ head/sys/kern/uipc_shm.c	Wed Jul 31 15:16:51 2019	(r350464)
@@ -729,7 +729,14 @@ kern_shm_open(struct thread *td, const char *userpath,
 	fdp = td->td_proc->p_fd;
 	cmode = (mode & ~fdp->fd_cmask) & ACCESSPERMS;
 
-	error = falloc_caps(td, &fp, &fd, O_CLOEXEC, fcaps);
+	/*
+	 * shm_open(2) created shm should always have O_CLOEXEC set, as mandated
+	 * by POSIX.  We allow it to be unset here so that an in-kernel
+	 * interface may be written as a thin layer around shm, optionally not
+	 * setting CLOEXEC.  For shm_open(2), O_CLOEXEC is set unconditionally
+	 * in sys_shm_open() to keep this implementation compliant.
+	 */
+	error = falloc_caps(td, &fp, &fd, flags & O_CLOEXEC, fcaps);
 	if (error)
 		return (error);
 
@@ -844,7 +851,8 @@ int
 sys_shm_open(struct thread *td, struct shm_open_args *uap)
 {
 
-	return (kern_shm_open(td, uap->path, uap->flags, uap->mode, NULL));
+	return (kern_shm_open(td, uap->path, uap->flags | O_CLOEXEC, uap->mode,
+	    NULL));
 }
 
 int