From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Thumshirn Subject: Re: scsi: use-after-free in bio_copy_from_iter Date: Tue, 6 Dec 2016 10:32:57 +0100 Message-ID: <20161206093257.GC4818@linux-x5ow.site> References: <20161203103802.dmvqzzquthwa7kd7@linux-x5ow.site> <20161203181948.GA3322@linux-x5ow.site> <20161205151753.GI8481@linux-x5ow.site> <20161205190339.GK1555@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Return-path: Content-Disposition: inline In-Reply-To: <20161205190339.GK1555@ZenIV.linux.org.uk> Sender: linux-block-owner@vger.kernel.org To: Al Viro Cc: Dmitry Vyukov , syzkaller , Doug Gilbert , jejb@linux.vnet.ibm.com, "Martin K. Petersen" , linux-scsi , LKML , axboe@kernel.dk, linux-block@vger.kernel.org, David Rientjes , Hannes Reinecke , mhocko@suse.cz List-Id: linux-scsi@vger.kernel.org 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@suse.de +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