svn commit: r363625 - stable/12/usr.sbin/mountd

[Rick Macklem]

Rick Macklem wrote:
>Ian Lepore wrote:
>>On Thu, 2020-07-30 at 01:52 +0000, Rick Macklem wrote:
>>> Brooks Davis wrote:
>>> > Author: brooks
>>> > Date: Mon Jul 27 23:18:14 2020
>>> > New Revision: 363625
>>> > URL: https://svnweb.freebsd.org/changeset/base/363625
>>> >
>>> > Log:
>>> >  MFC r363439:
>>> >
>>> >  Correct a type-mismatch between xdr_long and the variable "bad".
>>> >
>>> > [...]
>>> --> I can't see how the xdr.c code would work for a machine that is
>>> BIG_ENDIAN and where "long" is 64bits, but we don't have any of
>>> those.
>>>
>>
>>mips64 and powerpc64 are both big endian with 64-bit long.
>Oops, I didn't know that. In the past, I've run PowerPC and MIPS, but thought
>they both were little endian. (I recall the arches can be run either way.)
>
>Anyhow, take a look at head/lib/libc/xdr/xdr.c and it looks to me like it
>has been broken "forever" (ever since we stopped using a K&R compiler
>that would have always made "long" 32bits).
OK, I took another look at xdr.c and it isn't broken as I thought.

xdr_long() takes a "long *" argument ("long" in Sun XDR is 32bits),
but then it only passes it as an argument to XDR_PUTLONG(), which is actually
a call to xdrmem_putlong_aligned() or xdrmem_putlong_unaligned().
For xdrmem_putlong_aligned(), the line is:
       *(u_int32_t *)xdrs->x_private = htonl((u_int32_t)*lp);
      --> where lp is a "long *"

I'll admit I'm not 100% sure if "(u_int32_t)*lp" gets the correct 32bits of a 64bit
long pointer for all arches? (I'm not very good at knowing what type casts do.)
If this is the equivalent of "u_int32_t t; t = *lp; htonl(t); then I think the code is ok?
(At least it makes it clear that it is using 32bits of the value pointed to by the
 argument.)

For xdrmem_putlong_unaligned(), it does the same thing via:
        u_int32_t l;
        ….
        l = htonl((u_int32_t)*lp);

--> At least the man page for xdr_long() should be clarified to note it
      puts a 32bit quantity on the wire.

>If anyone has either of these and can set up an NFS server on one of
>them and then try and do an NFSv3 mount that is not allowed, it would
>be interesting to see the packet trace and if the MNT RPC fails, because
>it looks like it will put the high order 32bits on the wire and they'll
>always be 0?
It would still be interesting to test this on a 64bit big endian, but so long as
the above cast works, it does look like it works for all arches.

>Just to clarify. The behaviour wasn't broken by this commit. I just
>don't see how the commit fixes anything?
My mistake. Sorry for the noise.

I now think the commit is correct since it uses "*lp" to get the value before
casting it down to 32bits. Passing in an "int *" was incorrect.

The code does seem to handle "long *" for 64bit arches, although it
only puts 32bits "on-the-wire".

rick, who was confused because he knew there was only supposed to be
        32bits go on the wire.

-- Ian