v4.19.13 snapshot.
diff --git a/fs/fs_struct.c b/fs/fs_struct.c
new file mode 100644
index 0000000..be02507
--- /dev/null
+++ b/fs/fs_struct.c
@@ -0,0 +1,167 @@
+#include <linux/export.h>
+#include <linux/sched/signal.h>
+#include <linux/sched/task.h>
+#include <linux/fs.h>
+#include <linux/path.h>
+#include <linux/slab.h>
+#include <linux/fs_struct.h>
+#include "internal.h"
+
+/*
+ * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
+ * It can block.
+ */
+void set_fs_root(struct fs_struct *fs, const struct path *path)
+{
+ struct path old_root;
+
+ path_get(path);
+ spin_lock(&fs->lock);
+ write_seqcount_begin(&fs->seq);
+ old_root = fs->root;
+ fs->root = *path;
+ write_seqcount_end(&fs->seq);
+ spin_unlock(&fs->lock);
+ if (old_root.dentry)
+ path_put(&old_root);
+}
+
+/*
+ * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
+ * It can block.
+ */
+void set_fs_pwd(struct fs_struct *fs, const struct path *path)
+{
+ struct path old_pwd;
+
+ path_get(path);
+ spin_lock(&fs->lock);
+ write_seqcount_begin(&fs->seq);
+ old_pwd = fs->pwd;
+ fs->pwd = *path;
+ write_seqcount_end(&fs->seq);
+ spin_unlock(&fs->lock);
+
+ if (old_pwd.dentry)
+ path_put(&old_pwd);
+}
+
+static inline int replace_path(struct path *p, const struct path *old, const struct path *new)
+{
+ if (likely(p->dentry != old->dentry || p->mnt != old->mnt))
+ return 0;
+ *p = *new;
+ return 1;
+}
+
+void chroot_fs_refs(const struct path *old_root, const struct path *new_root)
+{
+ struct task_struct *g, *p;
+ struct fs_struct *fs;
+ int count = 0;
+
+ read_lock(&tasklist_lock);
+ do_each_thread(g, p) {
+ task_lock(p);
+ fs = p->fs;
+ if (fs) {
+ int hits = 0;
+ spin_lock(&fs->lock);
+ write_seqcount_begin(&fs->seq);
+ hits += replace_path(&fs->root, old_root, new_root);
+ hits += replace_path(&fs->pwd, old_root, new_root);
+ write_seqcount_end(&fs->seq);
+ while (hits--) {
+ count++;
+ path_get(new_root);
+ }
+ spin_unlock(&fs->lock);
+ }
+ task_unlock(p);
+ } while_each_thread(g, p);
+ read_unlock(&tasklist_lock);
+ while (count--)
+ path_put(old_root);
+}
+
+void free_fs_struct(struct fs_struct *fs)
+{
+ path_put(&fs->root);
+ path_put(&fs->pwd);
+ kmem_cache_free(fs_cachep, fs);
+}
+
+void exit_fs(struct task_struct *tsk)
+{
+ struct fs_struct *fs = tsk->fs;
+
+ if (fs) {
+ int kill;
+ task_lock(tsk);
+ spin_lock(&fs->lock);
+ tsk->fs = NULL;
+ kill = !--fs->users;
+ spin_unlock(&fs->lock);
+ task_unlock(tsk);
+ if (kill)
+ free_fs_struct(fs);
+ }
+}
+
+struct fs_struct *copy_fs_struct(struct fs_struct *old)
+{
+ struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
+ /* We don't need to lock fs - think why ;-) */
+ if (fs) {
+ fs->users = 1;
+ fs->in_exec = 0;
+ spin_lock_init(&fs->lock);
+ seqcount_init(&fs->seq);
+ fs->umask = old->umask;
+
+ spin_lock(&old->lock);
+ fs->root = old->root;
+ path_get(&fs->root);
+ fs->pwd = old->pwd;
+ path_get(&fs->pwd);
+ spin_unlock(&old->lock);
+ }
+ return fs;
+}
+
+int unshare_fs_struct(void)
+{
+ struct fs_struct *fs = current->fs;
+ struct fs_struct *new_fs = copy_fs_struct(fs);
+ int kill;
+
+ if (!new_fs)
+ return -ENOMEM;
+
+ task_lock(current);
+ spin_lock(&fs->lock);
+ kill = !--fs->users;
+ current->fs = new_fs;
+ spin_unlock(&fs->lock);
+ task_unlock(current);
+
+ if (kill)
+ free_fs_struct(fs);
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(unshare_fs_struct);
+
+int current_umask(void)
+{
+ return current->fs->umask;
+}
+EXPORT_SYMBOL(current_umask);
+
+/* to be mentioned only in INIT_TASK */
+struct fs_struct init_fs = {
+ .users = 1,
+ .lock = __SPIN_LOCK_UNLOCKED(init_fs.lock),
+ .seq = SEQCNT_ZERO(init_fs.seq),
+ .umask = 0022,
+};