* Re: [scsi] 6aded12b10: kernel_BUG_at_mm/usercopy.c
2022-03-23 15:40 ` [scsi] 6aded12b10: kernel_BUG_at_mm/usercopy.c Kees Cook
@ 2022-03-23 15:42 ` Matthew Wilcox
2022-03-23 22:30 ` Kees Cook
2022-03-23 15:47 ` Christoph Hellwig
2022-03-24 6:48 ` Christoph Hellwig
2 siblings, 1 reply; 6+ messages in thread
From: Matthew Wilcox @ 2022-03-23 15:42 UTC (permalink / raw)
To: Kees Cook
Cc: Christoph Hellwig, kernel test robot, Martin K. Petersen,
Bart Van Assche, John Garry, LKML, lkp, lkp, linux-mm,
linux-hardening
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@infradead.org/
>
> 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
>
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [scsi] 6aded12b10: kernel_BUG_at_mm/usercopy.c
2022-03-23 15:42 ` Matthew Wilcox
@ 2022-03-23 22:30 ` Kees Cook
0 siblings, 0 replies; 6+ messages in thread
From: Kees Cook @ 2022-03-23 22:30 UTC (permalink / raw)
To: Matthew Wilcox
Cc: Christoph Hellwig, kernel test robot, Martin K. Petersen,
Bart Van Assche, John Garry, LKML, lkp, lkp, linux-mm,
linux-hardening
On Wed, Mar 23, 2022 at 03:42:34PM +0000, Matthew Wilcox wrote:
> 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@infradead.org/
> >
> > 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.
LOL. Okay, you'd mentioned another check, so I wasn't sure. I can go
ahead and snag it, but I'll likely wait until the next window and let it
live in -next for a while, unless you think it should get YOLOed in. :)
-Kees
--
Kees Cook
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [scsi] 6aded12b10: kernel_BUG_at_mm/usercopy.c
2022-03-23 15:40 ` [scsi] 6aded12b10: kernel_BUG_at_mm/usercopy.c Kees Cook
2022-03-23 15:42 ` Matthew Wilcox
@ 2022-03-23 15:47 ` Christoph Hellwig
2022-03-23 22:33 ` Kees Cook
2022-03-24 6:48 ` Christoph Hellwig
2 siblings, 1 reply; 6+ messages in thread
From: Christoph Hellwig @ 2022-03-23 15:47 UTC (permalink / raw)
To: Kees Cook
Cc: Christoph Hellwig, kernel test robot, Martin K. Petersen,
Bart Van Assche, John Garry, LKML, lkp, lkp,
Matthew Wilcox (Oracle), linux-mm, linux-hardening
On Wed, Mar 23, 2022 at 08:40:30AM -0700, Kees Cook wrote:
> Regardless, I'm concerned that disabling PAGESPAN will just uncover
> further checks, though. Where is allocation happening? The check is here:
blk_mq_alloc_rqs, using alloc_pages_node. This hasn't actually changed
with this comment. Just the size of the allocation shrunk, probably
leading to the span of pages.
> 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?
scsi_ioctl_reset is the odd one out and does also allocate a request,
but that request is never used for user copies (and that whole hacky
side path needs to go away, there is a huge series that needs to be
finished to sort this out).
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [scsi] 6aded12b10: kernel_BUG_at_mm/usercopy.c
2022-03-23 15:47 ` Christoph Hellwig
@ 2022-03-23 22:33 ` Kees Cook
0 siblings, 0 replies; 6+ messages in thread
From: Kees Cook @ 2022-03-23 22:33 UTC (permalink / raw)
To: Christoph Hellwig
Cc: kernel test robot, Martin K. Petersen, Bart Van Assche,
John Garry, LKML, lkp, lkp, Matthew Wilcox (Oracle), linux-mm,
linux-hardening
On Wed, Mar 23, 2022 at 04:47:39PM +0100, Christoph Hellwig wrote:
> On Wed, Mar 23, 2022 at 08:40:30AM -0700, Kees Cook wrote:
> > Regardless, I'm concerned that disabling PAGESPAN will just uncover
> > further checks, though. Where is allocation happening? The check is here:
>
> blk_mq_alloc_rqs, using alloc_pages_node. This hasn't actually changed
> with this comment. Just the size of the allocation shrunk, probably
> leading to the span of pages.
Okay, the page allocator _should_ be fine for that. In the mean time,
lkp should probably just disable PAGESPAN.
> > 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?
>
> scsi_ioctl_reset is the odd one out and does also allocate a request,
> but that request is never used for user copies (and that whole hacky
> side path needs to go away, there is a huge series that needs to be
> finished to sort this out).
Gotcha!
--
Kees Cook
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [scsi] 6aded12b10: kernel_BUG_at_mm/usercopy.c
2022-03-23 15:40 ` [scsi] 6aded12b10: kernel_BUG_at_mm/usercopy.c Kees Cook
2022-03-23 15:42 ` Matthew Wilcox
2022-03-23 15:47 ` Christoph Hellwig
@ 2022-03-24 6:48 ` Christoph Hellwig
2 siblings, 0 replies; 6+ messages in thread
From: Christoph Hellwig @ 2022-03-24 6:48 UTC (permalink / raw)
To: Kees Cook
Cc: Christoph Hellwig, kernel test robot, Martin K. Petersen,
Bart Van Assche, John Garry, LKML, lkp, lkp,
Matthew Wilcox (Oracle), linux-mm, linux-hardening
On Wed, Mar 23, 2022 at 08:40:30AM -0700, Kees Cook wrote:
> This series removes it:
> https://lore.kernel.org/linux-hardening/20220110231530.665970-1-willy@infradead.org/
If HARDENED_USERCOPY_PAGESPAN is so broken we really should remove it
ASAP independent of the other patches in the series.
^ permalink raw reply [flat|nested] 6+ messages in thread