On Thu, Feb 07, 2013 at 10:58:25AM -0500, Chuck Lever wrote: > > On Feb 7, 2013, at 10:02 AM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > > > On Fri, Feb 01, 2013 at 05:43:44PM -0500, Chuck Lever wrote: > >> Clean up. This matches a similar API for the client side, and > >> keeps ULP fingers out the of the GSS mech switch. > >> > >> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx> > >> Acked-by: J. Bruce Fields <bfields@xxxxxxxxxx> > >> --- > >> > >> Bruce- > >> > >> This version of the patch follows the existing logic in > >> nfsd4_do_encode_secinfo(): If the RPC layer can't find GSS info > >> that matches an export security flavor, it assumes the flavor is > >> not a GSS pseudoflavor, and simply puts it on the wire. > >> > >> However, if the below XDR encoding logic is given a legitimate GSS > >> pseudoflavor but the RPC layer says it does not support that > >> pseudoflavor for some reason, then we leak GSS pseudoflavor numbers > >> onto the wire. > >> > >> I confirmed this happens by blacklisting rpcsec_gss_krb5, then > >> attempted a client transition from the pseudo-fs to a Kerberos-only > >> share. The client received a flavor list containing the Kerberos > >> pseudoflavor numbers, rather than GSS tuples. > >> > >> The encoder logic can check that each pseudoflavor is less than > >> MAXFLAVOR before writing it into the buffer, to prevent this. But > >> after "nflavs" is written into the XDR buffer, the encoder can't > >> skip writing flavor information into the buffer when it discovers > >> the RPC layer doesn't support that flavor. > >> > >> Is there some way of writing "nflavs" into the XDR buffer after > >> the loop that writes the flavor information is complete? > > > > Yes, you can save a pointer and then go back and fill that in--see > > encode_fattr for an example. > > Thanks, I will submit an additional patch that describes this issue and fixes it. > > I asked David Noveck, as one of the authors of RFC 3530, whether an NFS server should return a zero-length flavor list or an error if SECINFO can't find any flavors a client is allowed to use. His opinion was to return NFS4_OK and a zero-length flavor list. Fine with me for this code. (In practice though we should probably be warning somewhere (exportfs?) if somebody creates an export like that.) --b. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
