[NFS] [PATCH] knfsd : export : Fix bug of svc_export_parse()

[Wei Yongjun]

Nobody replied yet, but I think this is really a BUG of exportfs.
exportfs command does not check so strictly, so maybe some unreasonable
fh.key can be add to /proc/net/rpc/nfsd.fh/channel, but used this key to
find fh.handle, this always be fail and still retry.

It's this correct?

> When I export /dev/null as root, and mount it from client, mount ntf4 command will frozen.
>
> You can test it by following command:
> #exportfs -i -o fsid=0,no_root_squash,insecure,rw,async *:/dev/null
> #mount -t nfs4 127.0.0.1:/ /tmp
>
> This is because in svc_export_parse() function, if check_export return 
> false, after we reject the file handle, we must do cleanup the cache, 
> which is not a format error of file handle.
>
> Signed-off-by: Wei Yongjun <yjwei at cn.fujitsu.com>
>
> --- fs/nfsd/export.c.orig	2007-02-20 20:59:22.000000000 -0500
> +++ fs/nfsd/export.c	2007-03-16 01:04:16.000000000 -0400
> @@ -543,12 +543,13 @@ static int svc_export_parse(struct cache
>  		if (err) goto out;
>  		exp.ex_fsid = an_int;
>  
> -		err = check_export(nd.dentry->d_inode, exp.ex_flags);
> -		if (err) goto out;
> -
>  		err = fsloc_parse(&mesg, buf, &exp.ex_fslocs);
>  		if (err)
>  			goto out;
> +
> +		err = check_export(nd.dentry->d_inode, exp.ex_flags);
> +		if (err)
> +			set_bit(CACHE_NEGATIVE, &exp.h.flags);
>  	}
>  
>  	expp = svc_export_lookup(&exp);
>