[PATCH] HID: core: Correctly handle ReportSize being zero

[PATCH] HID: core: Correctly handle ReportSize being zero

[Marc Zyngier]

It appears that a ReportSize value of zero is legal, even if a bit
non-sensical. Most of the HID code seems to handle that gracefully,
except when computing the total size in bytes. When fed as input to
memset, this leads to some funky outcomes.

Detect the corner case and correctly compute the size.

Cc: stable@vger.kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 drivers/hid/hid-core.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index 359616e3efbb..d2ecc9c45255 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -1597,6 +1597,17 @@ static void hid_output_field(const struct hid_device *hid,
 	}
 }
 
+/*
+ * Compute the size of a report.
+ */
+static size_t hid_compute_report_size(struct hid_report *report)
+{
+	if (report->size)
+		return ((report->size - 1) >> 3) + 1;
+
+	return 0;
+}
+
 /*
  * Create a report. 'data' has to be allocated using
  * hid_alloc_report_buf() so that it has proper size.
@@ -1609,7 +1620,7 @@ void hid_output_report(struct hid_report *report, __u8 *data)
 	if (report->id > 0)
 		*data++ = report->id;
 
-	memset(data, 0, ((report->size - 1) >> 3) + 1);
+	memset(data, 0, hid_compute_report_size(report));
 	for (n = 0; n < report->maxfield; n++)
 		hid_output_field(report->device, report->field[n], data);
 }
@@ -1739,7 +1750,7 @@ int hid_report_raw_event(struct hid_device *hid, int type, u8 *data, u32 size,
 		csize--;
 	}
 
-	rsize = ((report->size - 1) >> 3) + 1;
+	rsize = hid_compute_report_size(report);
 
 	if (report_enum->numbered && rsize >= HID_MAX_BUFFER_SIZE)
 		rsize = HID_MAX_BUFFER_SIZE - 1;
-- 
2.27.0

Re: [PATCH] HID: core: Correctly handle ReportSize being zero

[Jiri Kosina]

On Sat, 29 Aug 2020, Marc Zyngier wrote:

> It appears that a ReportSize value of zero is legal, even if a bit
> non-sensical. Most of the HID code seems to handle that gracefully,
> except when computing the total size in bytes. When fed as input to
> memset, this leads to some funky outcomes.
> 
> Detect the corner case and correctly compute the size.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Marc Zyngier <maz@kernel.org>

Thanks Marc; Benjamin will be pushing this patch through his regression 
testing machinery, and if all is good, I'll push it for 5.9-rc still.

-- 
Jiri Kosina
SUSE Labs

Re: [PATCH] HID: core: Correctly handle ReportSize being zero

[Benjamin Tissoires]

On Tue, Sep 1, 2020 at 10:14 AM Jiri Kosina <jikos@kernel.org> wrote:
>
> On Sat, 29 Aug 2020, Marc Zyngier wrote:
>
> > It appears that a ReportSize value of zero is legal, even if a bit
> > non-sensical. Most of the HID code seems to handle that gracefully,
> > except when computing the total size in bytes. When fed as input to
> > memset, this leads to some funky outcomes.
> >
> > Detect the corner case and correctly compute the size.
> >
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
>
> Thanks Marc; Benjamin will be pushing this patch through his regression
> testing machinery, and if all is good, I'll push it for 5.9-rc still.

Test results were good. I have now pushed this patch to for-5.9/upstream-fixes

Cheers,
Benjamin

>
> --
> Jiri Kosina
> SUSE Labs
>