pidfs: support FS_IOC_GETVERSION

This will allow 32 bit userspace to detect when a given inode number has
been recycled and also to construct a unique 64 bit identifier.

Link: https://lore.kernel.org/r/20241129-work-pidfs-v2-3-61043d66fbce@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/pidfs.c b/fs/pidfs.c
index 71af820eafa5b798663789ce7758a7ffa9942aa2..8d62d900d20d37cab1de8879a6ce9f5f20b9e304 100644 (file)
--- a/fs/pidfs.c
+++ b/fs/pidfs.c
@@ -271,6 +271,14 @@ static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
        struct ns_common *ns_common = NULL;
        struct pid_namespace *pid_ns;
 
+       if (cmd == FS_IOC_GETVERSION) {
+               if (!arg)
+                       return -EINVAL;
+
+               __u32 __user *argp = (__u32 __user *)arg;
+               return put_user(file_inode(file)->i_generation, argp);
+       }
+
        task = get_pid_task(pid, PIDTYPE_PID);
        if (!task)
                return -ESRCH;