Re: [PATCH 07/11] vfs: add cross-rename

[Andy Lutomirski]

On Wed, Nov 20, 2013 at 5:01 AM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> From: Miklos Szeredi <mszeredi@xxxxxxx>
>
> If flags contain RENAME_EXCHANGE then exchange source and destination files.
> There's no restriction on the type of the files; e.g. a directory can be
> exchanged with a symlink.

What happens if both RENAME_EXCHANGE and RENAME_NOREPLACE are set?

--Andy

>
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
> ---
>  fs/dcache.c             |  46 +++++++++++++++++----
>  fs/namei.c              | 107 +++++++++++++++++++++++++++++++++---------------
>  include/linux/dcache.h  |   1 +
>  include/uapi/linux/fs.h |   1 +
>  security/security.c     |  16 ++++++++
>  5 files changed, 131 insertions(+), 40 deletions(-)
>
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 0a38ef8d7f00..ea2fca1a2ec9 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -2527,12 +2527,14 @@ static void switch_names(struct dentry *dentry, struct dentry *target)
>                         dentry->d_name.name = dentry->d_iname;
>                 } else {
>                         /*
> -                        * Both are internal.  Just copy target to dentry
> +                        * Both are internal.
>                          */
> -                       memcpy(dentry->d_iname, target->d_name.name,
> -                                       target->d_name.len + 1);
> -                       dentry->d_name.len = target->d_name.len;
> -                       return;
> +                       unsigned int i;
> +                       BUILD_BUG_ON(!IS_ALIGNED(DNAME_INLINE_LEN, sizeof(long)));
> +                       for (i = 0; i < DNAME_INLINE_LEN / sizeof(long); i++) {
> +                               swap(((long *) &dentry->d_iname)[i],
> +                                    ((long *) &target->d_iname)[i]);
> +                       }
>                 }
>         }
>         swap(dentry->d_name.len, target->d_name.len);
> @@ -2589,13 +2591,15 @@ static void dentry_unlock_parents_for_move(struct dentry *dentry,
>   * __d_move - move a dentry
>   * @dentry: entry to move
>   * @target: new dentry
> + * @exchange: exchange the two dentries
>   *
>   * Update the dcache to reflect the move of a file name. Negative
>   * dcache entries should not be moved in this way. Caller must hold
>   * rename_lock, the i_mutex of the source and target directories,
>   * and the sb->s_vfs_rename_mutex if they differ. See lock_rename().
>   */
> -static void __d_move(struct dentry * dentry, struct dentry * target)
> +static void __d_move(struct dentry *dentry, struct dentry *target,
> +                    bool exchange)
>  {
>         if (!dentry->d_inode)
>                 printk(KERN_WARNING "VFS: moving negative dcache entry\n");
> @@ -2619,6 +2623,10 @@ static void __d_move(struct dentry * dentry, struct dentry * target)
>
>         /* Unhash the target: dput() will then get rid of it */
>         __d_drop(target);
> +       if (exchange) {
> +               __d_rehash(target,
> +                          d_hash(dentry->d_parent, dentry->d_name.hash));
> +       }
>
>         list_del(&dentry->d_u.d_child);
>         list_del(&target->d_u.d_child);
> @@ -2645,6 +2653,8 @@ static void __d_move(struct dentry * dentry, struct dentry * target)
>         write_seqcount_end(&dentry->d_seq);
>
>         dentry_unlock_parents_for_move(dentry, target);
> +       if (exchange)
> +               fsnotify_d_move(target);
>         spin_unlock(&target->d_lock);
>         fsnotify_d_move(dentry);
>         spin_unlock(&dentry->d_lock);
> @@ -2662,11 +2672,31 @@ static void __d_move(struct dentry * dentry, struct dentry * target)
>  void d_move(struct dentry *dentry, struct dentry *target)
>  {
>         write_seqlock(&rename_lock);
> -       __d_move(dentry, target);
> +       __d_move(dentry, target, false);
>         write_sequnlock(&rename_lock);
>  }
>  EXPORT_SYMBOL(d_move);
>
> +/*
> + * d_exchange - exchange two dentries
> + * @dentry1: first dentry
> + * @dentry2: second dentry
> + */
> +void d_exchange(struct dentry *dentry1, struct dentry *dentry2)
> +{
> +       write_seqlock(&rename_lock);
> +
> +       WARN_ON(!dentry1->d_inode);
> +       WARN_ON(!dentry2->d_inode);
> +       WARN_ON(IS_ROOT(dentry1));
> +       WARN_ON(IS_ROOT(dentry2));
> +
> +       __d_move(dentry1, dentry2, true);
> +
> +       write_sequnlock(&rename_lock);
> +}
> +
> +
>  /**
>   * d_ancestor - search for an ancestor
>   * @p1: ancestor dentry
> @@ -2714,7 +2744,7 @@ static struct dentry *__d_unalias(struct inode *inode,
>         m2 = &alias->d_parent->d_inode->i_mutex;
>  out_unalias:
>         if (likely(!d_mountpoint(alias))) {
> -               __d_move(alias, dentry);
> +               __d_move(alias, dentry, false);
>                 ret = alias;
>         }
>  out_err:
> diff --git a/fs/namei.c b/fs/namei.c
> index 5b41d4bfecd1..c23621255df0 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -4025,6 +4025,8 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
>         const unsigned char *old_name;
>         struct inode *source = old_dentry->d_inode;
>         struct inode *target = new_dentry->d_inode;
> +       bool new_is_dir = false;
> +       unsigned max_links = new_dir->i_sb->s_max_links;
>
>         if (source == target)
>                 return 0;
> @@ -4033,10 +4035,16 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
>         if (error)
>                 return error;
>
> -       if (!target)
> +       if (!target) {
>                 error = may_create(new_dir, new_dentry);
> -       else
> -               error = may_delete(new_dir, new_dentry, is_dir);
> +       } else {
> +               new_is_dir = d_is_dir(new_dentry);
> +
> +               if (!(flags & RENAME_EXCHANGE))
> +                       error = may_delete(new_dir, new_dentry, is_dir);
> +               else
> +                       error = may_delete(new_dir, new_dentry, new_is_dir);
> +       }
>         if (error)
>                 return error;
>
> @@ -4047,10 +4055,17 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
>          * If we are going to change the parent - check write permissions,
>          * we'll need to flip '..'.
>          */
> -       if (is_dir && new_dir != old_dir) {
> -               error = inode_permission(source, MAY_WRITE);
> -               if (error)
> -                       return error;
> +       if (new_dir != old_dir) {
> +               if (is_dir) {
> +                       error = inode_permission(source, MAY_WRITE);
> +                       if (error)
> +                               return error;
> +               }
> +               if ((flags & RENAME_EXCHANGE) && new_is_dir) {
> +                       error = inode_permission(target, MAY_WRITE);
> +                       if (error)
> +                               return error;
> +               }
>         }
>
>         error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry,
> @@ -4060,25 +4075,24 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
>
>         old_name = fsnotify_oldname_init(old_dentry->d_name.name);
>         dget(new_dentry);
> -       if (!is_dir)
> -               lock_two_nondirectories(source, target);
> -       else if (target)
> -               mutex_lock(&target->i_mutex);
> +       if (!(flags & RENAME_EXCHANGE)) {
> +               if (!is_dir)
> +                       lock_two_nondirectories(source, target);
> +               else if (target)
> +                       mutex_lock(&target->i_mutex);
> +       }
>
>         error = -EBUSY;
>         if (d_mountpoint(old_dentry) || d_mountpoint(new_dentry))
>                 goto out;
>
> -       if (is_dir) {
> -               unsigned max_links = new_dir->i_sb->s_max_links;
> -
> +       if (max_links && new_dir != old_dir) {
>                 error = -EMLINK;
> -               if (max_links && !target && new_dir != old_dir &&
> -                   new_dir->i_nlink >= max_links)
> +               if (is_dir && !new_is_dir && new_dir->i_nlink >= max_links)
> +                       goto out;
> +               if ((flags & RENAME_EXCHANGE) && !is_dir && new_is_dir &&
> +                   old_dir->i_nlink > max_links)
>                         goto out;
> -
> -               if (target)
> -                       shrink_dcache_parent(new_dentry);
>         } else {
>                 error = try_break_deleg(source, delegated_inode);
>                 if (error)
> @@ -4089,27 +4103,40 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
>                                 goto out;
>                 }
>         }
> +       if (is_dir && !(flags & RENAME_EXCHANGE) && target)
> +               shrink_dcache_parent(new_dentry);
>         error = old_dir->i_op->rename(old_dir, old_dentry, new_dir, new_dentry,
>                                       flags);
>         if (error)
>                 goto out;
>
> -       if (target) {
> +       if (!(flags & RENAME_EXCHANGE) && target) {
>                 if (is_dir)
>                         target->i_flags |= S_DEAD;
>                 dont_mount(new_dentry);
>         }
> -       if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE))
> -               d_move(old_dentry, new_dentry);
> +       if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE)) {
> +               if (!(flags & RENAME_EXCHANGE))
> +                       d_move(old_dentry, new_dentry);
> +               else
> +                       d_exchange(old_dentry, new_dentry);
> +       }
>  out:
> -       if (!is_dir)
> -               unlock_two_nondirectories(source, target);
> -       else if (target)
> -               mutex_unlock(&target->i_mutex);
> +       if (!(flags & RENAME_EXCHANGE)) {
> +               if (!is_dir)
> +                       unlock_two_nondirectories(source, target);
> +               else if (target)
> +                       mutex_unlock(&target->i_mutex);
> +       }
>         dput(new_dentry);
> -       if (!error)
> +       if (!error) {
>                 fsnotify_move(old_dir, new_dir, old_name, is_dir,
> -                             target, old_dentry);
> +                             !(flags & RENAME_EXCHANGE) ? target : NULL, old_dentry);
> +               if (flags & RENAME_EXCHANGE) {
> +                       fsnotify_move(new_dir, old_dir, old_dentry->d_name.name,
> +                                     new_is_dir, NULL, new_dentry);
> +               }
> +       }
>         fsnotify_oldname_free(old_name);
>
>         return error;
> @@ -4129,9 +4156,12 @@ SYSCALL_DEFINE5(renameat2, int, olddfd, const char __user *, oldname,
>         bool should_retry = false;
>         int error;
>
> -       if (flags & ~RENAME_NOREPLACE)
> +       if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
>                 return -EOPNOTSUPP;
>
> +       if ((flags & RENAME_NOREPLACE) && (flags & RENAME_EXCHANGE))
> +               return -EINVAL;
> +
>  retry:
>         from = user_path_parent(olddfd, oldname, &oldnd, lookup_flags);
>         if (IS_ERR(from)) {
> @@ -4166,7 +4196,8 @@ retry:
>
>         oldnd.flags &= ~LOOKUP_PARENT;
>         newnd.flags &= ~LOOKUP_PARENT;
> -       newnd.flags |= LOOKUP_RENAME_TARGET;
> +       if (!(flags & RENAME_EXCHANGE))
> +               newnd.flags |= LOOKUP_RENAME_TARGET;
>
>  retry_deleg:
>         trap = lock_rename(new_dir, old_dir);
> @@ -4186,12 +4217,23 @@ retry_deleg:
>         error = -EEXIST;
>         if ((flags & RENAME_NOREPLACE) && d_is_positive(new_dentry))
>                 goto exit5;
> +       if (flags & RENAME_EXCHANGE) {
> +               error = -ENOENT;
> +               if (!new_dentry->d_inode)
> +                       goto exit5;
> +
> +               if (!d_is_dir(new_dentry)) {
> +                       error = -ENOTDIR;
> +                       if (newnd.last.name[newnd.last.len])
> +                               goto exit5;
> +               }
> +       }
>         /* unless the source is a directory trailing slashes give -ENOTDIR */
>         if (!d_is_dir(old_dentry)) {
>                 error = -ENOTDIR;
>                 if (oldnd.last.name[oldnd.last.len])
>                         goto exit5;
> -               if (newnd.last.name[newnd.last.len])
> +               if (!(flags & RENAME_EXCHANGE) && newnd.last.name[newnd.last.len])
>                         goto exit5;
>         }
>         /* source should not be ancestor of target */
> @@ -4199,7 +4241,8 @@ retry_deleg:
>         if (old_dentry == trap)
>                 goto exit5;
>         /* target should not be an ancestor of source */
> -       error = -ENOTEMPTY;
> +       if (!(flags & RENAME_EXCHANGE))
> +               error = -ENOTEMPTY;
>         if (new_dentry == trap)
>                 goto exit5;
>
> diff --git a/include/linux/dcache.h b/include/linux/dcache.h
> index 901616910e0a..87e14e698f89 100644
> --- a/include/linux/dcache.h
> +++ b/include/linux/dcache.h
> @@ -306,6 +306,7 @@ extern void dentry_update_name_case(struct dentry *, struct qstr *);
>
>  /* used for rename() and baskets */
>  extern void d_move(struct dentry *, struct dentry *);
> +extern void d_exchange(struct dentry *, struct dentry *);
>  extern struct dentry *d_ancestor(struct dentry *, struct dentry *);
>
>  /* appendix may either be NULL or be used for transname suffixes */
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 9250f4dd7d96..ca1a11bb4443 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -36,6 +36,7 @@
>  #define SEEK_MAX       SEEK_HOLE
>
>  #define RENAME_NOREPLACE       (1 << 0)        /* Don't overwrite target */
> +#define RENAME_EXCHANGE                (1 << 1)        /* Exchange source and dest */
>
>  struct fstrim_range {
>         __u64 start;
> diff --git a/security/security.c b/security/security.c
> index d00ae28dea76..0ef72cd2255f 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -439,6 +439,14 @@ int security_path_rename(struct path *old_dir, struct dentry *old_dentry,
>         if (unlikely(IS_PRIVATE(old_dentry->d_inode) ||
>                      (new_dentry->d_inode && IS_PRIVATE(new_dentry->d_inode))))
>                 return 0;
> +
> +       if (flags & RENAME_EXCHANGE) {
> +               int err = security_ops->path_rename(new_dir, new_dentry,
> +                                                   old_dir, old_dentry);
> +               if (err)
> +                       return err;
> +       }
> +
>         return security_ops->path_rename(old_dir, old_dentry, new_dir,
>                                          new_dentry);
>  }
> @@ -531,6 +539,14 @@ int security_inode_rename(struct inode *old_dir, struct dentry *old_dentry,
>          if (unlikely(IS_PRIVATE(old_dentry->d_inode) ||
>              (new_dentry->d_inode && IS_PRIVATE(new_dentry->d_inode))))
>                 return 0;
> +
> +       if (flags & RENAME_EXCHANGE) {
> +               int err = security_ops->inode_rename(new_dir, new_dentry,
> +                                                    old_dir, old_dentry);
> +               if (err)
> +                       return err;
> +       }
> +
>         return security_ops->inode_rename(old_dir, old_dentry,
>                                            new_dir, new_dentry);
>  }
> --
> 1.8.1.4
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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