On Wed, Apr 21, 2010 at 06:35:27PM -0400, J. Bruce Fields wrote: > On Tue, Apr 20, 2010 at 03:39:44PM -0400, J. Bruce Fields wrote: > > On Tue, Apr 20, 2010 at 03:24:59PM -0400, William A. (Andy) Adamson wrote: > > > On Tue, Apr 20, 2010 at 12:51 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: > > > > On Tue, Apr 20, 2010 at 12:16:52PM +1000, Neil Brown wrote: > > > >> > > > >> Surely this can never have worked... which implies that the code has > > > >> never been used? > > > >> > > > >> When read_buf is called to move over to the next page in the pagelist > > > >> of an NFSv4 request, it sets argp->end to essentially a random > > > >> number, certainly not an address within the page which argp->p now > > > >> points to. So subsequent calls to READ_BUF will think there is much > > > >> more than a page of spare space (the cast to u32 ensures an unsigned > > > >> comparison) so we can expect to fall off the end of the second > > > >> page. > > > > > > > > Yipes, thanks. > > > > > > > >> I guess we never ever receive requests with any operation starting > > > >> beyond the first page! > > > > > > > > putfh-write-getattr, for example, is common enough. The write decoding > > > > should leave arg->end set correctly. But there are two read_buf()'s in > > > > decode_getattr(), and I can't see why we don't hit this bug on a write > > > > that leaves that final getattr exactly straddling a page boundary. > > > > > > The write data is dumped into the rq_vec which has non-contiguous > > > pages. So the xdr_buf head only holds the putfh result, the short > > > write response header (v4 stateid, offset, how, length, etc), and then > > > the getattr. so there is plenty of space. > > > > This is the server-side write-decoding, so you could see: > > > > > > rpc header | putfh | write ... data ... | getattr > > ^ > > | > > page boundary here > > Hm, I guess even when argp->end is wrong, argp->p is always set to > something sane; so on the next READ_BUF(), when you hit the > > nbytes <= (u32)((char *)argp->end - (char *)argp->p > > case, you do > > p = argp->p; > argp->p += XDR_QUADLEN(nbytes); > > and p is something reasonable. "end" stays wrong, but that won't be a > problem until you run past the end of the *next* page, which it would > take a very unusual compound to do. (Nevertheless: applied, for 2.6.34 and stable.) --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
