On Fri, 2008-05-02 at 11:56 -0400, J. Bruce Fields wrote:
> On Fri, May 02, 2008 at 11:34:39AM -0400, Christoph Hellwig wrote:
> > On Fri, May 02, 2008 at 05:16:46PM +0200, Frank van Maarseveen wrote:
> > > A privileged process on an NFS client which drops privileges after using
> > > them to change the current working directory, will experience incorrect
> > > EACCES after an NFS server reboot. This problem can also occur after
> > > memory pressure on the server, particularly when the client side is
> > > quiet for some time.
> > >
> > > This patch removes the x-bit check during dentry tree reconstruction at
> > > the server by exportfs on behalf of nfsd.
> >
> > I'm still against adding this crap,
>
> The only statements I've seen against the change so far have been of the
> form "you should not do that", without explaining why not.
>
> It's entirely possible that you're right, but I need some argument.
AFAICS, the real problem here is that nfsd is dropping its privileged
mode too early. Why can't you call reconnect_path() using nfsd's root
permissions instead of dropping permissions checks altogether?
> > and even when I get overruled that
> > doesn't make the comments on lookup_one_noperm any less true,
>
> We do need to at least update it to reflect the addition of a new
> caller.
>
> > not does it give you a permit to break the kerneldoc generation.
>
> Oops; here's a version that should make kerneldoc happy. It also adds a
> little more explanation, and leaves alone the editorializing on sysfs
> (on which I have no opinion).
>
> --b.
>
> commit ccdfe77dc49a07c298bb9e2107290267492f16b3
> Author: Frank van Maarseveen <frankvm@xxxxxxxxxxx>
> Date: Fri May 2 17:16:46 2008 +0200
>
> exportfs: fix incorrect EACCES in reconnect_path()
>
> A privileged process on an NFS client which drops privileges after using
> them to change the current working directory, will experience incorrect
> EACCES after an NFS server reboot. This problem can also occur after
> memory pressure on the server, particularly when the client side is
> quiet for some time.
>
> This patch removes the x-bit check during dentry tree reconstruction at
> the server by exportfs on behalf of nfsd.
>
> Signed-off-by: Frank van Maarseveen <frankvm@xxxxxxxxxxx>
> Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxxxxxx>
>
> diff --git a/fs/exportfs/expfs.c b/fs/exportfs/expfs.c
> index 109ab5e..89dc7ae 100644
> --- a/fs/exportfs/expfs.c
> +++ b/fs/exportfs/expfs.c
> @@ -170,7 +170,7 @@ reconnect_path(struct vfsmount *mnt, struct dentry *target_dir)
> }
> dprintk("%s: found name: %s\n", __FUNCTION__, nbuf);
> mutex_lock(&ppd->d_inode->i_mutex);
> - npd = lookup_one_len(nbuf, ppd, strlen(nbuf));
> + npd = lookup_one_noperm(nbuf, ppd);
> mutex_unlock(&ppd->d_inode->i_mutex);
> if (IS_ERR(npd)) {
> err = PTR_ERR(npd);
> @@ -447,8 +447,7 @@ struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
> err = exportfs_get_name(mnt, target_dir, nbuf, result);
> if (!err) {
> mutex_lock(&target_dir->d_inode->i_mutex);
> - nresult = lookup_one_len(nbuf, target_dir,
> - strlen(nbuf));
> + nresult = lookup_one_noperm(nbuf, target_dir);
> mutex_unlock(&target_dir->d_inode->i_mutex);
> if (!IS_ERR(nresult)) {
> if (nresult->d_inode) {
> diff --git a/fs/namei.c b/fs/namei.c
> index e179f71..c00150c 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -1391,7 +1391,7 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
> }
>
> /**
> - * lookup_one_noperm - bad hack for sysfs
> + * lookup_one_noperm - bad hack for sysfs and nfsd
> * @name: pathname component to lookup
> * @base: base directory to lookup from
> *
> @@ -1399,7 +1399,12 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len)
> * checks. It's a horrible hack to work around the braindead sysfs
> * architecture and should not be used anywhere else.
> *
> - * DON'T USE THIS FUNCTION EVER, thanks.
> + * It is also used by nfsd via exports to reconstruct the dentry tree
> + * for directory handles (e.g. when a client requests a directory by
> + * filehandle after a server reboot has cleared the dentry cache of that
> + * directory's parents).
> + *
> + * DON'T USE THIS FUNCTION ANYWHERE ELSE, thanks.
> */
> struct dentry *lookup_one_noperm(const char *name, struct dentry *base)
> {
How about if exportfs is compiled as a module?
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