Re: [autofs] [PATCH 1/7] autofs4: Save autofs trigger's vfsmount in super block info

[Ian Kent]

On Wed, Dec 23, 2009 at 03:36:57PM -0800, Valerie Aurora wrote:
> From: Jan Blunck <jblu...@suse.de>
> 
> This is a bugfix/replacement for commit
> 051d381259eb57d6074d02a6ba6e90e744f1a29f:
> 
>     During a path walk if an autofs trigger is mounted on a dentry,
>     when the follow_link method is called, the nameidata struct
>     contains the vfsmount and mountpoint dentry of the parent mount
>     while the dentry that is passed in is the root of the autofs
>     trigger mount.  I believe it is impossible to get the vfsmount of
>     the trigger mount, within the follow_link method, when only the
>     parent vfsmount and the root dentry of the trigger mount are
>     known.
> 
> The solution in this commit was to replace the path embedded in the
> parent's nameidata with the path of the link itself in
> __do_follow_link().  This is a relatively harmless misuse of the
> field, but union mounts ran into a bug during follow_link() caused by
> the nameidata containing the wrong path (we count on it being what it
> is all other places - the path of the parent).
> 
> A cleaner and easier to understand solution is to save the necessary
> vfsmount in the autofs superblock info when it is mounted.  Then we
> can easily update the vfsmount in autofs4_follow_link().
> 
> Signed-off-by: Jan Blunck <jblu...@suse.de>
> Signed-off-by: Valerie Aurora <vaur...@redhat.com>
Acked-by: <ra...@themaw.net>

Don't know how I missed such an obvious solution when I did this.
Thanks, Ian

> Cc: Ian Kent <ra...@themaw.net>
> Cc: autofs@linux.kernel.org
> Cc: Alexander Viro <v...@zeniv.linux.org.uk>
> ---
>  fs/autofs4/autofs_i.h |    1 +
>  fs/autofs4/init.c     |   11 ++++++++++-
>  fs/autofs4/root.c     |    6 ++++++
>  fs/namei.c            |    7 ++-----
>  4 files changed, 19 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h
> index 8f7cdde..db2bfce 100644
> --- a/fs/autofs4/autofs_i.h
> +++ b/fs/autofs4/autofs_i.h
> @@ -130,6 +130,7 @@ struct autofs_sb_info {
>       int reghost_enabled;
>       int needs_reghost;
>       struct super_block *sb;
> +     struct vfsmount *mnt;
>       struct mutex wq_mutex;
>       spinlock_t fs_lock;
>       struct autofs_wait_queue *queues; /* Wait queue pointer */
> diff --git a/fs/autofs4/init.c b/fs/autofs4/init.c
> index 9722e4b..5e0dcd7 100644
> --- a/fs/autofs4/init.c
> +++ b/fs/autofs4/init.c
> @@ -17,7 +17,16 @@
>  static int autofs_get_sb(struct file_system_type *fs_type,
>       int flags, const char *dev_name, void *data, struct vfsmount *mnt)
>  {
> -     return get_sb_nodev(fs_type, flags, data, autofs4_fill_super, mnt);
> +     struct autofs_sb_info *sbi;
> +     int ret;
> +
> +     ret = get_sb_nodev(fs_type, flags, data, autofs4_fill_super, mnt);
> +     if (ret)
> +             return ret;
> +
> +     sbi = autofs4_sbi(mnt->mnt_sb);
> +     sbi->mnt = mnt;
> +     return 0;
>  }
>  
>  static struct file_system_type autofs_fs_type = {
> diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
> index b96a3c5..cb991b8 100644
> --- a/fs/autofs4/root.c
> +++ b/fs/autofs4/root.c
> @@ -179,6 +179,12 @@ static void *autofs4_follow_link(struct dentry *dentry, 
> struct nameidata *nd)
>       DPRINTK("dentry=%p %.*s oz_mode=%d nd->flags=%d",
>               dentry, dentry->d_name.len, dentry->d_name.name, oz_mode,
>               nd->flags);
> +
> +     dput(nd->path.dentry);
> +     mntput(nd->path.mnt);
> +     nd->path.mnt = mntget(sbi->mnt);
> +     nd->path.dentry = dget(dentry);
> +
>       /*
>        * For an expire of a covered direct or offset mount we need
>        * to break out of follow_down() at the autofs mount trigger
> diff --git a/fs/namei.c b/fs/namei.c
> index d11f404..c768444 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -629,11 +629,8 @@ static __always_inline int __do_follow_link(struct path 
> *path, struct nameidata
>       touch_atime(path->mnt, dentry);
>       nd_set_link(nd, NULL);
>  
> -     if (path->mnt != nd->path.mnt) {
> -             path_to_nameidata(path, nd);
> -             dget(dentry);
> -     }
> -     mntget(path->mnt);
> +     if (path->mnt == nd->path.mnt)
> +             mntget(nd->path.mnt);
>       cookie = dentry->d_inode->i_op->follow_link(dentry, nd);
>       error = PTR_ERR(cookie);
>       if (!IS_ERR(cookie)) {
> -- 
> 1.5.6.5
> 

_______________________________________________
autofs mailing list
autofs@linux.kernel.org
http://linux.kernel.org/mailman/listinfo/autofs