On Wed, Mar 23, 2022 at 08:40:30AM -0700, Kees Cook wrote: > On Wed, Mar 23, 2022 at 08:14:10AM +0100, Christoph Hellwig wrote: > > The actual warning is; > > > > [ 34.496096][ T331] usercopy: Kernel memory overwrite attempt detected to spans multiple pages (off set 0, size 6)! > > > > This is for the cmnd field in struct scsi_cmnd, which is allocated by > > the block layer as part of the request allocator. So with a specific > > packing it can legitimately span pages. > > > > Kees: how can we annotate that this is ok? > > The main problem is that CONFIG_HARDENED_USERCOPY_PAGESPAN=y is broken > (and nothing should be setting it). > > This series removes it: > https://lore.kernel.org/linux-hardening/20220110231530.665970-1-willy@xxxxxxxxxxxxx/ > > Matthew, what's the status of that series? Will it make the current > merge window? I thought you were going to merge it! I haven't put it in any of my public trees. > As for the SCSI changes, I'm a bit worried about type confusion, as I > don't see anything actually validating types/sizes when converting: > > static inline void *blk_mq_rq_to_pdu(struct request *rq) > { > return rq + 1; > } > > But I guess that ship has sailed. :P > > Regardless, I'm concerned that disabling PAGESPAN will just uncover > further checks, though. Where is allocation happening? The check is here: > > static int scsi_fill_sghdr_rq(struct scsi_device *sdev, struct request *rq, > struct sg_io_hdr *hdr, fmode_t mode) > { > struct scsi_cmnd *scmd = blk_mq_rq_to_pdu(rq); > > if (hdr->cmd_len < 6) > return -EMSGSIZE; > if (copy_from_user(scmd->cmnd, hdr->cmdp, hdr->cmd_len)) > return -EFAULT; > ... > } > > I don't see any earlier marking for this copy_from_user(), so I assume > the old allocation was a plain kmalloc(). > > For comparision, a related marking can be seen for a copy_to_user() case > in commit 0afe76e88c57 ("scsi: Define usercopy region in scsi_sense_cache > slab cache") > > I *think* the allocation is happening in scsi_ioctl_reset()? But that's > a plain kmalloc(), so I'm not sure why PAGESPAN would have tripped... > are there other allocation paths? > > -- > Kees Cook >
