On Thu, Jul 30, 2020 at 03:48:34PM +0000, Rick Macklem wrote: > 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.
Thank you for all the analysis. I'd initially changed all the uses of bad to use xdr_int(), but switched to this "fix" because it's what NetBSD and OpenBSD have been using for over a decade (and there was less churn). I'm happy to flip it the other way if that seems more correct/less confusing. The previous code does in fact cause a 64-bit load of a pointer to an int on 64-bit platforms. I hit this in CheriBSD because that pointer had 4-byte bounds. -- Brooks
signature.asc
Description: PGP signature