drm/amdgpu: Fix buffer overflow in INFO ioctl

The values for "se_num" and "sh_num" come from the user in the ioctl.
They can be in the 0-255 range but if they're more than
AMDGPU_GFX_MAX_SE (4) or AMDGPU_GFX_MAX_SH_PER_SE (2) then it results in
an out of bounds read.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -669,8 +669,12 @@ static int amdgpu_info_ioctl(struct drm_device *dev, void *data, struct drm_file
 		 * in the bitfields */
 		if (se_num == AMDGPU_INFO_MMR_SE_INDEX_MASK)
 			se_num = 0xffffffff;
+		else if (se_num >= AMDGPU_GFX_MAX_SE)
+			return -EINVAL;
 		if (sh_num == AMDGPU_INFO_MMR_SH_INDEX_MASK)
 			sh_num = 0xffffffff;
+		else if (sh_num >= AMDGPU_GFX_MAX_SH_PER_SE)
+			return -EINVAL;
 
 		if (info->read_mmr_reg.count > 128)
 			return -EINVAL;