drm/amd/pm: Handle non-terminated overdrive commands.

The incoming strings might not be terminated by a newline
or a 0.

(found while testing a program that just wrote the string
 itself, causing a crash)

Cc: stable@vger.kernel.org
Fixes: e3933f26b6 ("drm/amd/pp: Add edit/commit/show OD clock/voltage support in sysfs")
Signed-off-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/pm/amdgpu_pm.c

@@ -761,7 +761,7 @@ static ssize_t amdgpu_set_pp_od_clk_voltage(struct device *dev,
 	if (adev->in_suspend && !adev->in_runpm)
 		return -EPERM;
 
-	if (count > 127)
+	if (count > 127 || count == 0)
 		return -EINVAL;
 
 	if (*buf == 's')
@@ -781,7 +781,8 @@ static ssize_t amdgpu_set_pp_od_clk_voltage(struct device *dev,
 	else
 		return -EINVAL;
 
-	memcpy(buf_cpy, buf, count+1);
+	memcpy(buf_cpy, buf, count);
+	buf_cpy[count] = 0;
 
 	tmp_str = buf_cpy;
 
@@ -798,6 +799,9 @@ static ssize_t amdgpu_set_pp_od_clk_voltage(struct device *dev,
 			return -EINVAL;
 		parameter_size++;
 
+		if (!tmp_str)
+			break;
+
 		while (isspace(*tmp_str))
 			tmp_str++;
 	}