On Wed, 10 Jul 2013, Benjamin Tissoires wrote:
> > implement() is setting bytes in LE data stream. In case the data
> > is not aligned to 64bits, it reads past the allocated buffer. It
> > doesn't really change any value there (it's properly bitmasked), but
> > in case that this read past the boundary hits a page boundary, pagefault
> > happens when accessing 64bits of 'x' in implement(), and kernel oopses.
> >
> > This happens much more often when numbered reports are in use, as the
> > initial 8bit skip in the buffer makes the whole process work on values
> > which are not aligned to 64bits.
> >
> > This problem dates back to attempts in 2005 and 2006 to make implement()
> > and extract() as generic as possible, and even back then the problem
> > was realized by Adam Kroperlin, but falsely assumed to be impossible
> > to cause any harm:
> >
> >
> > http://www.mail-archive.com/linux-usb-devel@lists.sourceforge.net/msg47690.html
> >
> > I have made several attempts at fixing it "on the spot" directly in
> > implement(), but the results were horrible; the special casing for
> > processing
> > last 64bit chunk and switching to different math makes it unreadable mess.
> >
> > I therefore took a path to allocate a few bytes more which will never make
> > it into final report, but are there as a cushion for all the 64bit math
> > operations happening in implement() and extract().
> >
> > All callers of hid_output_report() are converted at the same time to
> > allocate
> > the buffer by newly introduced hid_alloc_report_buf() helper.
> >
> > Signed-off-by: Jiri Kosina <jkos...@suse.cz>
> > ---
>
> Thanks for that. It should (I hope) fix the bugs we are seeing from time
> to times under Fedora and that I was not able to answer:
> https://bugzilla.redhat.com/show_bug.cgi?id=965280
> https://bugzilla.redhat.com/show_bug.cgi?id=927488
> https://bugzilla.redhat.com/show_bug.cgi?id=881504
965280 and 881504 absolutely look like an incarnation of this very
problem. The faulting address is pagesize aligned (i.e. the loop just
crossed the boundary), and the faulting code is the
put_unaligned_access_le64().
Exactly the same as the report I had.
927488 seems like a different bug to me -- not an address on page
boundary, and we're not faulting in implement().
> I have a small remark for usbhid:
>
> > drivers/hid/hid-core.c | 19 ++++++++++++++++++-
> > drivers/hid/hid-logitech-dj.c | 12 ++++++++++--
> > drivers/hid/hid-picolcd_debugfs.c | 10 +++++++++-
> > drivers/hid/usbhid/hid-core.c | 4 ++--
> > include/linux/hid.h | 1 +
> > net/bluetooth/hidp/core.c | 14 +++++++++-----
> > 6 files changed, 49 insertions(+), 11 deletions(-)
>
> [snipped]
>
> > diff --git a/drivers/hid/usbhid/hid-core.c b/drivers/hid/usbhid/hid-core.c
> > index 9941828..2b0b96daf 100644
> > --- a/drivers/hid/usbhid/hid-core.c
> > +++ b/drivers/hid/usbhid/hid-core.c
> > @@ -546,7 +546,7 @@ static void __usbhid_submit_report(struct hid_device
> > *hid, struct hid_report *re
> > return;
> > }
> >
> > - usbhid->out[usbhid->outhead].raw_report = kmalloc(len,
> > GFP_ATOMIC);
> > + usbhid->out[usbhid->outhead].raw_report =
> > hid_alloc_report_buf(report, GFP_ATOMIC);
> > if (!usbhid->out[usbhid->outhead].raw_report) {
> > hid_warn(hid, "output queueing failed\n");
> > return;
> > @@ -595,7 +595,7 @@ static void __usbhid_submit_report(struct hid_device
> > *hid, struct hid_report *re
> > }
> >
> > if (dir == USB_DIR_OUT) {
> > - usbhid->ctrl[usbhid->ctrlhead].raw_report = kmalloc(len,
> > GFP_ATOMIC);
> > + usbhid->ctrl[usbhid->ctrlhead].raw_report =
> > hid_alloc_report_buf(report, GFP_ATOMIC);
>
> line 538: int len = ((report->size - 1) >> 3) + 1 + (report->id > 0);
> is not used anywhere after applying the patch. It can be dropped.
Good catch.
> Besides the picolcd problems spotted by Bruno:
> Reviewed-by: Benjamin Tissoires <benjamin.tissoi...@redhat.com>
Thanks.
--
Jiri Kosina
SUSE Labs
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