drm/amdgpu: Prevent random memory access in FRU code

Prevent random memory access in the FRU EEPROM code by passing the size of
the destination buffer to the reading routine, and reading no more than the
size of the buffer.

Cc: Kent Russell <kent.russell@amd.com>
Cc: Alex Deucher <Alexander.Deucher@amd.com>
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Acked-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
Reviewed-by: Kent Russell <kent.russell@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_fru_eeprom.c

@@ -30,7 +30,6 @@
 #include "amdgpu_eeprom.h"
 
 #define FRU_EEPROM_MADDR        0x60000
-#define I2C_PRODUCT_INFO_OFFSET 0xC0
 
 static bool is_fru_eeprom_supported(struct amdgpu_device *adev)
 {
@@ -77,9 +76,10 @@ static bool is_fru_eeprom_supported(struct amdgpu_device *adev)
 }
 
 static int amdgpu_fru_read_eeprom(struct amdgpu_device *adev, uint32_t addrptr,
-				  unsigned char *buf)
+				  unsigned char *buf, size_t buf_size)
 {
-	int ret, size;
+	int ret;
+	u8 size;
 
 	ret = amdgpu_eeprom_read(adev->pm.fru_eeprom_i2c_bus, addrptr, buf, 1);
 	if (ret < 1) {
@@ -90,9 +90,11 @@ static int amdgpu_fru_read_eeprom(struct amdgpu_device *adev, uint32_t addrptr,
 	/* The size returned by the i2c requires subtraction of 0xC0 since the
 	 * size apparently always reports as 0xC0+actual size.
 	 */
-	size = buf[0] - I2C_PRODUCT_INFO_OFFSET;
+	size = buf[0] & 0x3F;
+	size = min_t(size_t, size, buf_size);
 
-	ret = amdgpu_eeprom_read(adev->pm.fru_eeprom_i2c_bus, addrptr + 1, buf, size);
+	ret = amdgpu_eeprom_read(adev->pm.fru_eeprom_i2c_bus, addrptr + 1,
+				 buf, size);
 	if (ret < 1) {
 		DRM_WARN("FRU: Failed to get data field");
 		return ret;
@@ -129,7 +131,7 @@ int amdgpu_fru_get_product_info(struct amdgpu_device *adev)
 	 * and the language field, so just start from 0xb, manufacturer size
 	 */
 	addrptr = FRU_EEPROM_MADDR + 0xb;
-	size = amdgpu_fru_read_eeprom(adev, addrptr, buf);
+	size = amdgpu_fru_read_eeprom(adev, addrptr, buf, sizeof(buf));
 	if (size < 1) {
 		DRM_ERROR("Failed to read FRU Manufacturer, ret:%d", size);
 		return -EINVAL;
@@ -139,7 +141,7 @@ int amdgpu_fru_get_product_info(struct amdgpu_device *adev)
 	 * size field being 1 byte. This pattern continues below.
 	 */
 	addrptr += size + 1;
-	size = amdgpu_fru_read_eeprom(adev, addrptr, buf);
+	size = amdgpu_fru_read_eeprom(adev, addrptr, buf, sizeof(buf));
 	if (size < 1) {
 		DRM_ERROR("Failed to read FRU product name, ret:%d", size);
 		return -EINVAL;
@@ -155,7 +157,7 @@ int amdgpu_fru_get_product_info(struct amdgpu_device *adev)
 	adev->product_name[len] = '\0';
 
 	addrptr += size + 1;
-	size = amdgpu_fru_read_eeprom(adev, addrptr, buf);
+	size = amdgpu_fru_read_eeprom(adev, addrptr, buf, sizeof(buf));
 	if (size < 1) {
 		DRM_ERROR("Failed to read FRU product number, ret:%d", size);
 		return -EINVAL;
@@ -173,7 +175,7 @@ int amdgpu_fru_get_product_info(struct amdgpu_device *adev)
 	adev->product_number[len] = '\0';
 
 	addrptr += size + 1;
-	size = amdgpu_fru_read_eeprom(adev, addrptr, buf);
+	size = amdgpu_fru_read_eeprom(adev, addrptr, buf, sizeof(buf));
 
 	if (size < 1) {
 		DRM_ERROR("Failed to read FRU product version, ret:%d", size);
@@ -181,7 +183,7 @@ int amdgpu_fru_get_product_info(struct amdgpu_device *adev)
 	}
 
 	addrptr += size + 1;
-	size = amdgpu_fru_read_eeprom(adev, addrptr, buf);
+	size = amdgpu_fru_read_eeprom(adev, addrptr, buf, sizeof(buf));
 
 	if (size < 1) {
 		DRM_ERROR("Failed to read FRU serial number, ret:%d", size);