On Wed, 2 Dec 2009, Jeff Layton wrote:
> procfs-style symlinks return a last_type of LAST_BIND without an actual
> path string. This causes __follow_link to skip calling __vfs_follow_link
> and so the dentry isn't revalidated.
>
> This is a problem when the link target sits on NFSv4 as it depends on
> the VFS to revalidate the dentry before using it on an open call. Ensure
> that this occurs by forcing a revalidation of the target dentry of
> LAST_BIND symlinks.
An added advantage is that the symlinks in /proc will show the
invalidated path as "(deleted)". Maybe proc_pid_readlink() should
also call force_reval_path() to get an up-to-date state of the path?
Acked-by: Miklos Szeredi <mszeredi@xxxxxxx>
>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
> fs/namei.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
> 1 files changed, 45 insertions(+), 0 deletions(-)
>
> diff --git a/fs/namei.c b/fs/namei.c
> index 3374917..339789e 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -414,6 +414,46 @@ do_revalidate(struct dentry *dentry, struct nameidata *nd)
> }
>
> /*
> + * force_reval_path - force revalidation of a dentry
> + *
> + * In some situations the path walking code will trust dentries without
> + * revalidating them. This causes problems for filesystems that depend on
> + * d_revalidate to handle file opens (e.g. NFSv4). When FS_REVAL_DOT is set
> + * (which indicates that it's possible for the dentry to go stale), force
> + * a d_revalidate call before proceeding.
> + *
> + * Returns 0 if the revalidation was successful. If the revalidation fails,
> + * either return the error returned by d_revalidate or -ESTALE if the
> + * revalidation it just returned 0. If d_revalidate returns 0, we attempt to
> + * invalidate the dentry. It's up to the caller to handle putting references
> + * to the path if necessary.
> + */
> +static int
> +force_reval_path(struct path *path, struct nameidata *nd)
> +{
> + int status;
> + struct dentry *dentry = path->dentry;
> +
> + /*
> + * only check on filesystems where it's possible for the dentry to
> + * become stale. It's assumed that if this flag is set then the
> + * d_revalidate op will also be defined.
> + */
> + if (!(dentry->d_sb->s_type->fs_flags & FS_REVAL_DOT))
> + return 0;
> +
> + status = dentry->d_op->d_revalidate(dentry, nd);
> + if (status > 0)
> + return 0;
> +
> + if (!status) {
> + d_invalidate(dentry);
> + status = -ESTALE;
> + }
> + return status;
> +}
> +
> +/*
> * Internal lookup() using the new generic dcache.
> * SMP-safe
> */
> @@ -641,6 +681,11 @@ static __always_inline int __do_follow_link(struct path *path, struct nameidata
> error = 0;
> if (s)
> error = __vfs_follow_link(nd, s);
> + else if (nd->last_type == LAST_BIND) {
> + error = force_reval_path(&nd->path, nd);
> + if (error)
> + path_put(&nd->path);
> + }
> if (dentry->d_inode->i_op->put_link)
> dentry->d_inode->i_op->put_link(dentry, nd, cookie);
> }
> --
> 1.5.5.6
>
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