diff mbox series

[v3,2/2] drm/bridge: ti-sn65dsi86: Never store more than msg->size bytes in AUX xfer

Message ID 20231214123752.v3.2.I7b83c0f31aeedc6b1dc98c7c741d3e1f94f040f8@changeid
State New
Headers
Series [v3,1/2] drm/bridge: parade-ps8640: Never store more than msg->size bytes in AUX xfer |

Commit Message

Doug Anderson Dec. 14, 2023, 8:37 p.m. UTC 
  For aux reads, the value `msg->size` indicates the size of the buffer
provided by `msg->buffer`. We should never in any circumstances write
more bytes to the buffer since it may overflow the buffer.

In the ti-sn65dsi86 driver there is one code path that reads the
transfer length from hardware. Even though it's never been seen to be
a problem, we should make extra sure that the hardware isn't
increasing the length since doing so would cause us to overrun the
buffer.

Fixes: 982f589bde7a ("drm/bridge: ti-sn65dsi86: Update reply on aux failures")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

(no changes since v2)

Changes in v2:
- Updated patch subject to match ps8640 patch.

 drivers/gpu/drm/bridge/ti-sn65dsi86.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Comments

Guenter Roeck Dec. 14, 2023, 9:28 p.m. UTC | #1 
On Thu, Dec 14, 2023 at 12:38 PM Douglas Anderson <dianders@chromium.org> wrote:
>
> For aux reads, the value `msg->size` indicates the size of the buffer
> provided by `msg->buffer`. We should never in any circumstances write
> more bytes to the buffer since it may overflow the buffer.
>
> In the ti-sn65dsi86 driver there is one code path that reads the
> transfer length from hardware. Even though it's never been seen to be
> a problem, we should make extra sure that the hardware isn't
> increasing the length since doing so would cause us to overrun the
> buffer.
>
> Fixes: 982f589bde7a ("drm/bridge: ti-sn65dsi86: Update reply on aux failures")
> Signed-off-by: Douglas Anderson <dianders@chromium.org>

Reviewed-by: Guenter Roeck <groeck@chromium.org>

> ---
>
> (no changes since v2)
>
> Changes in v2:
> - Updated patch subject to match ps8640 patch.
>
>  drivers/gpu/drm/bridge/ti-sn65dsi86.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> index 9095d1453710..62cc3893dca5 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> @@ -527,6 +527,7 @@ static ssize_t ti_sn_aux_transfer(struct drm_dp_aux *aux,
>         u32 request_val = AUX_CMD_REQ(msg->request);
>         u8 *buf = msg->buffer;
>         unsigned int len = msg->size;
> +       unsigned int short_len;
>         unsigned int val;
>         int ret;
>         u8 addr_len[SN_AUX_LENGTH_REG + 1 - SN_AUX_ADDR_19_16_REG];
> @@ -600,7 +601,8 @@ static ssize_t ti_sn_aux_transfer(struct drm_dp_aux *aux,
>         }
>
>         if (val & AUX_IRQ_STATUS_AUX_SHORT) {
> -               ret = regmap_read(pdata->regmap, SN_AUX_LENGTH_REG, &len);
> +               ret = regmap_read(pdata->regmap, SN_AUX_LENGTH_REG, &short_len);
> +               len = min(len, short_len);
>                 if (ret)
>                         goto exit;
>         } else if (val & AUX_IRQ_STATUS_NAT_I2C_FAIL) {
> --
> 2.43.0.472.g3155946c3a-goog
>
Stephen Boyd Dec. 17, 2023, 1:08 a.m. UTC | #2 
Quoting Douglas Anderson (2023-12-14 12:37:52)
> For aux reads, the value `msg->size` indicates the size of the buffer
> provided by `msg->buffer`. We should never in any circumstances write
> more bytes to the buffer since it may overflow the buffer.
>
> In the ti-sn65dsi86 driver there is one code path that reads the
> transfer length from hardware. Even though it's never been seen to be
> a problem, we should make extra sure that the hardware isn't
> increasing the length since doing so would cause us to overrun the
> buffer.
>
> Fixes: 982f589bde7a ("drm/bridge: ti-sn65dsi86: Update reply on aux failures")
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---

Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Doug Anderson Dec. 18, 2023, 4:48 p.m. UTC | #3 
Hi,

On Thu, Dec 14, 2023 at 12:38 PM Douglas Anderson <dianders@chromium.org> wrote:
>
> For aux reads, the value `msg->size` indicates the size of the buffer
> provided by `msg->buffer`. We should never in any circumstances write
> more bytes to the buffer since it may overflow the buffer.
>
> In the ti-sn65dsi86 driver there is one code path that reads the
> transfer length from hardware. Even though it's never been seen to be
> a problem, we should make extra sure that the hardware isn't
> increasing the length since doing so would cause us to overrun the
> buffer.
>
> Fixes: 982f589bde7a ("drm/bridge: ti-sn65dsi86: Update reply on aux failures")
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
>
> (no changes since v2)
>
> Changes in v2:
> - Updated patch subject to match ps8640 patch.
>
>  drivers/gpu/drm/bridge/ti-sn65dsi86.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)

Since the patch fixes a potential crash, has two Reviews (even if
they're both from @chromium), and doesn't seem controversial, I didn't
want a full week and just landed it in drm-misc-fixes. If anyone is
upset by this then please shout and we can revert or I can post a
followup patch.

Pushed to drm-misc-fixes:

aca58eac52b8 drm/bridge: ti-sn65dsi86: Never store more than msg->size
bytes in AUX xfer
diff mbox series

Patch

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
index 9095d1453710..62cc3893dca5 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
@@ -527,6 +527,7 @@  static ssize_t ti_sn_aux_transfer(struct drm_dp_aux *aux,
 	u32 request_val = AUX_CMD_REQ(msg->request);
 	u8 *buf = msg->buffer;
 	unsigned int len = msg->size;
+	unsigned int short_len;
 	unsigned int val;
 	int ret;
 	u8 addr_len[SN_AUX_LENGTH_REG + 1 - SN_AUX_ADDR_19_16_REG];
@@ -600,7 +601,8 @@  static ssize_t ti_sn_aux_transfer(struct drm_dp_aux *aux,
 	}
 
 	if (val & AUX_IRQ_STATUS_AUX_SHORT) {
-		ret = regmap_read(pdata->regmap, SN_AUX_LENGTH_REG, &len);
+		ret = regmap_read(pdata->regmap, SN_AUX_LENGTH_REG, &short_len);
+		len = min(len, short_len);
 		if (ret)
 			goto exit;
 	} else if (val & AUX_IRQ_STATUS_NAT_I2C_FAIL) {