Re: [PATCH v2 2/2] drm/bridge: ti-sn65dsi86: Never store more than msg->size bytes in AUX xfer

[Robert Foss]

On Thu, Dec 14, 2023 at 9:32 PM Douglas Anderson  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 
> ---
>
> 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, );
> +   ret = regmap_read(pdata->regmap, SN_AUX_LENGTH_REG, 
> _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
>
>

Reviewed-by: Robert Foss 

[PATCH v2 2/2] drm/bridge: ti-sn65dsi86: Never store more than msg->size bytes in AUX xfer

[Douglas Anderson]

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 
---

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, );
+   ret = regmap_read(pdata->regmap, SN_AUX_LENGTH_REG, _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