pidfs: move O_RDWR into pidfs_alloc_file()

Since all pidfds must be O_RDWR currently enfore that directly in the
file allocation function itself instead of letting callers specify it.

Link: https://lore.kernel.org/[email protected]
Tested-by: Luca Boccassi <[email protected]>
Reviewed-by: Oleg Nesterov <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

Author: brauner

fs/pidfs.c

@@ -892,6 +892,7 @@ struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags)
 		return ERR_PTR(-ESRCH);
 
 	flags &= ~PIDFD_STALE;
+	flags |= O_RDWR;
 	pidfd_file = dentry_open(&path, flags, current_cred());
 	/* Raise PIDFD_THREAD explicitly as do_dentry_open() strips it. */
 	if (!IS_ERR(pidfd_file))