Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

Pull proc fix from Eric Biederman:
 "A brown paper bag slipped through my proc changes, and syzcaller
  caught it when the code ended up in your tree.

  I have opted to fix it the simplest cleanest way I know how, so there
  is no reasonable chance for the bug to repeat"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
  proc: Use a dedicated lock in struct pid

fs/proc/base.c

@@ -1839,9 +1839,9 @@ void proc_pid_evict_inode(struct proc_inode *ei)
 	struct pid *pid = ei->pid;
 
 	if (S_ISDIR(ei->vfs_inode.i_mode)) {
-		spin_lock(&pid->wait_pidfd.lock);
+		spin_lock(&pid->lock);
 		hlist_del_init_rcu(&ei->sibling_inodes);
-		spin_unlock(&pid->wait_pidfd.lock);
+		spin_unlock(&pid->lock);
 	}
 
 	put_pid(pid);
@@ -1877,9 +1877,9 @@ struct inode *proc_pid_make_inode(struct super_block * sb,
 	/* Let the pid remember us for quick removal */
 	ei->pid = pid;
 	if (S_ISDIR(mode)) {
-		spin_lock(&pid->wait_pidfd.lock);
+		spin_lock(&pid->lock);
 		hlist_add_head_rcu(&ei->sibling_inodes, &pid->inodes);
-		spin_unlock(&pid->wait_pidfd.lock);
+		spin_unlock(&pid->lock);
 	}
 
 	task_dump_owner(task, 0, &inode->i_uid, &inode->i_gid);
@@ -3273,7 +3273,7 @@ static const struct inode_operations proc_tgid_base_inode_operations = {
 
 void proc_flush_pid(struct pid *pid)
 {
-	proc_invalidate_siblings_dcache(&pid->inodes, &pid->wait_pidfd.lock);
+	proc_invalidate_siblings_dcache(&pid->inodes, &pid->lock);
 	put_pid(pid);
 }
 

include/linux/pid.h

@@ -60,6 +60,7 @@ struct pid
 {
 	refcount_t count;
 	unsigned int level;
+	spinlock_t lock;
 	/* lists of tasks that use this pid */
 	struct hlist_head tasks[PIDTYPE_MAX];
 	struct hlist_head inodes;

kernel/pid.c

@@ -256,6 +256,7 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
 
 	get_pid_ns(ns);
 	refcount_set(&pid->count, 1);
+	spin_lock_init(&pid->lock);
 	for (type = 0; type < PIDTYPE_MAX; ++type)
 		INIT_HLIST_HEAD(&pid->tasks[type]);