- make pidfd_create() static.

- Don't pass O_RDWR | O_CLOEXEC to __pidfd_prepare() in copy_process(),
  __pidfd_prepare() adds these flags unconditionally.

- Kill the flags check in __pidfd_prepare(). sys_pidfd_open() checks the
  flags itself, all other users of pidfd_prepare() pass flags = 0.

  If we need a sanity check for those other in kernel users then
  WARN_ON_ONCE(flags & ~PIDFD_NONBLOCK) makes more sense.

- Don't pass O_RDWR to get_unused_fd_flags(), it ignores everything except
  O_CLOEXEC.

- Don't pass O_CLOEXEC to anon_inode_getfile(), it ignores everything except
  O_ACCMODE | O_NONBLOCK.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 include/linux/pid.h | 1 -
 kernel/fork.c       | 9 +++------
 kernel/pid.c        | 2 +-
 3 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/include/linux/pid.h b/include/linux/pid.h
index 395cacce1179..e6a041cb8bac 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -73,7 +73,6 @@ struct file;
 extern struct pid *pidfd_pid(const struct file *file);
 struct pid *pidfd_get_pid(unsigned int fd, unsigned int *flags);
 struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags);
-int pidfd_create(struct pid *pid, unsigned int flags);
 int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret);
 
 static inline struct pid *get_pid(struct pid *pid)
diff --git a/kernel/fork.c b/kernel/fork.c
index c981fa6171c1..347641398f9d 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2130,15 +2130,12 @@ static int __pidfd_prepare(struct pid *pid, unsigned int flags, struct file **re
 	int pidfd;
 	struct file *pidfd_file;
 
-	if (flags & ~(O_NONBLOCK | O_RDWR | O_CLOEXEC))
-		return -EINVAL;
-
-	pidfd = get_unused_fd_flags(O_RDWR | O_CLOEXEC);
+	pidfd = get_unused_fd_flags(O_CLOEXEC);
 	if (pidfd < 0)
 		return pidfd;
 
 	pidfd_file = anon_inode_getfile("[pidfd]", &pidfd_fops, pid,
-					flags | O_RDWR | O_CLOEXEC);
+					flags | O_RDWR);
 	if (IS_ERR(pidfd_file)) {
 		put_unused_fd(pidfd);
 		return PTR_ERR(pidfd_file);
@@ -2524,7 +2521,7 @@ __latent_entropy struct task_struct *copy_process(
 	 */
 	if (clone_flags & CLONE_PIDFD) {
 		/* Note that no task has been attached to @pid yet. */
-		retval = __pidfd_prepare(pid, O_RDWR | O_CLOEXEC, &pidfile);
+		retval = __pidfd_prepare(pid, 0, &pidfile);
 		if (retval < 0)
 			goto bad_fork_free_pid;
 		pidfd = retval;
diff --git a/kernel/pid.c b/kernel/pid.c
index b52b10865454..c7a3e359f8f5 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -595,7 +595,7 @@ struct task_struct *pidfd_get_task(int pidfd, unsigned int *flags)
  * Return: On success, a cloexec pidfd is returned.
  *         On error, a negative errno number will be returned.
  */
-int pidfd_create(struct pid *pid, unsigned int flags)
+static int pidfd_create(struct pid *pid, unsigned int flags)
 {
 	int pidfd;
 	struct file *pidfd_file;
-- 
2.25.1.362.g51ebf55

On Thu, 25 Jan 2024 17:17:34 +0100, Oleg Nesterov wrote:
> - make pidfd_create() static.
> 
> - Don't pass O_RDWR | O_CLOEXEC to __pidfd_prepare() in copy_process(),
>   __pidfd_prepare() adds these flags unconditionally.
> 
> - Kill the flags check in __pidfd_prepare(). sys_pidfd_open() checks the
>   flags itself, all other users of pidfd_prepare() pass flags = 0.
> 
> [...]

Thanks!

---

Applied to the vfs.misc branch of the vfs/vfs.git tree.
Patches in the vfs.misc branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.misc

[1/1] pidfd: cleanup the usage of __pidfd_prepare's flags
      https://git.kernel.org/vfs/vfs/c/2502da713861

On 01/25, Christian Brauner wrote:
>
> Applied to the vfs.misc branch of the vfs/vfs.git tree.

OK, thanks.

This can also simplify the possible PIDFD_THREAD change we discuss.

Oleg.

On Thu, Jan 25, 2024 at 05:53:22PM +0100, Oleg Nesterov wrote:
> On 01/25, Christian Brauner wrote:
> >
> > Applied to the vfs.misc branch of the vfs/vfs.git tree.
> 
> OK, thanks.
> 
> This can also simplify the possible PIDFD_THREAD change we discuss.

Sounds good. Thanks for cleaning the flags bit up.