On Mon, Dec 05, 2016 at 07:03:39PM +0000, Al Viro wrote: > On Mon, Dec 05, 2016 at 04:17:53PM +0100, Johannes Thumshirn wrote: > > 633 hp = &srp->header; > > [...] > > 646 hp->dxferp = (char __user *)buf + cmd_size; > > > So the memory for hp->dxferp comes from: > > 633 hp = &srp->header; > > ???? > > > >From my debug instrumentation I see that the dxferp ends up in the > > iovec_iter's kvec->iov_base and the faulting address is always dxferp + n * > > 4k with n in [1, 16] (and we're copying 16 4k pages from the iovec into the > > bio). > > _Address_ of hp->dxferp comes from that assignment; the value is 'buf' > argument of sg_write() + small offset. In this case, it should point > inside a pipe buffer, which is, indeed, at a kernel address. Who'd > allocated srp is irrelevant. Yes I realized that as well when I had enough distance between me and the code... > > And if you end up dereferencing more than one page worth there, you do have > a problem - pipe buffers are not going to be that large. Could you slap > WARN_ON((size_t)input_size > count); > right after the calculation of input_size in sg_write() and see if it triggers > on your reproducer? I did and it didn't trigger. What triggers is (as expected) a WARN_ON((size_t)mxsize > count); We have count at 80 and mxsize (which ends in hp->dxfer_len) at 65499. But the 65499 bytes are the len of the data we're suppost to be copying in via the iov. I'm still rather confused what's happening here, sorry. -- Johannes Thumshirn Storage jthumshirn@xxxxxxx +49 911 74053 689 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: Felix Imendörffer, Jane Smithard, Graham Norton HRB 21284 (AG Nürnberg) Key fingerprint = EC38 9CAB C2C4 F25D 8600 D0D0 0393 969D 2D76 0850 -- To unsubscribe from this list: send the line "unsubscribe linux-block" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
