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Date: Tue, 19 Jan 2016 12:31:18 +0100
From: Benjamin Tissoires <benjamin.tissoires@...hat.com>
To: Dmitry Torokhov <dtor@...omium.org>
Cc: Jiri Kosina <jikos@...nel.org>, linux-input@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] HID: fix out of bound access in extract and implement
On Jan 18 2016 or thereabouts, Dmitry Torokhov wrote:
> extract() and implement() access buffer containing reports in 64-bit
> chunks, but there is no guarantee that buffers are padded to 64 bit
> boundary. In fact, KASAN has caught such OOB access with i2c-hid and
> Synaptics touch controller.
>
> Instead of trying to hunt all parties that allocate buffers and make
> sure they are padded, let's switch extract() and implement() to byte
> access. It is a bit slower, bit we are not dealing with super fast
> devices here.
>
> Also let's fix link to the HID spec while we are at it.
>
> Signed-off-by: Dmitry Torokhov <dtor@...omium.org>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
Thanks Dmitry!
Speaking about KASAN, I recently had a weird bug report for a Logitech
T650 which switched by itself back into the mouse emulation mode. I run
KASAN today and found a followup patch in hid_input_field() which
prevent some out of bound readings. I'll send this this afternoon.
Cheers,
Benjamin
> ---
> drivers/hid/hid-core.c | 90 ++++++++++++++++++++++++++++++++++++--------------
> 1 file changed, 66 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
> index 9e182e4..9f1019d 100644
> --- a/drivers/hid/hid-core.c
> +++ b/drivers/hid/hid-core.c
> @@ -1075,7 +1075,7 @@ static u32 s32ton(__s32 value, unsigned n)
> * Extract/implement a data field from/to a little endian report (bit array).
> *
> * Code sort-of follows HID spec:
> - * http://www.usb.org/developers/devclass_docs/HID1_11.pdf
> + * http://www.usb.org/developers/hidpage/HID1_11.pdf
> *
> * While the USB HID spec allows unlimited length bit fields in "report
> * descriptors", most devices never use more than 16 bits.
> @@ -1083,20 +1083,37 @@ static u32 s32ton(__s32 value, unsigned n)
> * Search linux-kernel and linux-usb-devel archives for "hid-core extract".
> */
>
> -__u32 hid_field_extract(const struct hid_device *hid, __u8 *report,
> - unsigned offset, unsigned n)
> -{
> - u64 x;
> +static u32 __extract(u8 *report, unsigned offset, int n)
> +{
> + unsigned int idx = offset / 8;
> + unsigned int bit_nr = 0;
> + unsigned int bit_shift = offset % 8;
> + int bits_to_copy = 8 - bit_shift;
> + u32 value = 0;
> + u32 mask = n < 32 ? (1U << n) - 1 : ~0U;
> +
> + while (n > 0) {
> + value |= ((u32)report[idx] >> bit_shift) << bit_nr;
> + n -= bits_to_copy;
> + bit_nr += bits_to_copy;
> + bits_to_copy = 8;
> + bit_shift = 0;
> + idx++;
> + }
> +
> + return value & mask;
> +}
>
> - if (n > 32)
> +u32 hid_field_extract(const struct hid_device *hid, u8 *report,
> + unsigned offset, unsigned n)
> +{
> + if (n > 32) {
> hid_warn(hid, "hid_field_extract() called with n (%d) > 32! (%s)\n",
> n, current->comm);
> + n = 32;
> + }
>
> - report += offset >> 3; /* adjust byte index */
> - offset &= 7; /* now only need bit offset into one byte */
> - x = get_unaligned_le64(report);
> - x = (x >> offset) & ((1ULL << n) - 1); /* extract bit field */
> - return (u32) x;
> + return __extract(report, offset, n);
> }
> EXPORT_SYMBOL_GPL(hid_field_extract);
>
> @@ -1106,31 +1123,56 @@ EXPORT_SYMBOL_GPL(hid_field_extract);
> * The data mangled in the bit stream remains in little endian
> * order the whole time. It make more sense to talk about
> * endianness of register values by considering a register
> - * a "cached" copy of the little endiad bit stream.
> + * a "cached" copy of the little endian bit stream.
> */
> -static void implement(const struct hid_device *hid, __u8 *report,
> - unsigned offset, unsigned n, __u32 value)
> +
> +static void __implement(u8 *report, unsigned offset, int n, u32 value)
> +{
> + unsigned int idx = offset / 8;
> + unsigned int size = offset + n;
> + unsigned int bit_shift = offset % 8;
> + int bits_to_set = 8 - bit_shift;
> + u8 bit_mask = 0xff << bit_shift;
> +
> + while (n - bits_to_set >= 0) {
> + report[idx] &= ~bit_mask;
> + report[idx] |= value << bit_shift;
> + value >>= bits_to_set;
> + n -= bits_to_set;
> + bits_to_set = 8;
> + bit_mask = 0xff;
> + bit_shift = 0;
> + idx++;
> + }
> +
> + /* last nibble */
> + if (n) {
> + if (size % 8)
> + bit_mask &= (1U << (size % 8)) - 1;
> + report[idx] &= ~bit_mask;
> + report[idx] |= (value << bit_shift) & bit_mask;
> + }
> +}
> +
> +static void implement(const struct hid_device *hid, u8 *report,
> + unsigned offset, unsigned n, u32 value)
> {
> - u64 x;
> - u64 m = (1ULL << n) - 1;
> + u64 m;
>
> - if (n > 32)
> + if (n > 32) {
> hid_warn(hid, "%s() called with n (%d) > 32! (%s)\n",
> __func__, n, current->comm);
> + n = 32;
> + }
>
> + m = (1ULL << n) - 1;
> if (value > m)
> hid_warn(hid, "%s() called with too large value %d! (%s)\n",
> __func__, value, current->comm);
> WARN_ON(value > m);
> value &= m;
>
> - report += offset >> 3;
> - offset &= 7;
> -
> - x = get_unaligned_le64(report);
> - x &= ~(m << offset);
> - x |= ((u64)value) << offset;
> - put_unaligned_le64(x, report);
> + __implement(report, offset, n, value);
> }
>
> /*
> --
> 2.6.0.rc2.230.g3dd15c0
>
>
> --
> Dmitry
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