[PATCH 5.7 167/179] drm/amdgpu: Fix NULL dereference in dpm sysfs handlers

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

From: Paweł Gronowski <me@xxxxxxxxxx>

commit 38e0c89a19fd13f28d2b4721035160a3e66e270b upstream.

NULL dereference occurs when string that is not ended with space or
newline is written to some dpm sysfs interface (for example pp_dpm_sclk).
This happens because strsep replaces the tmp with NULL if the delimiter
is not present in string, which is then dereferenced by tmp[0].

Reproduction example:
sudo sh -c 'echo -n 1 > /sys/class/drm/card0/device/pp_dpm_sclk'

Signed-off-by: Paweł Gronowski <me@xxxxxxxxxx>
Signed-off-by: Alex Deucher <alexander.deucher@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_pm.c
@@ -775,8 +775,7 @@ static ssize_t amdgpu_set_pp_od_clk_volt
 		tmp_str++;
 	while (isspace(*++tmp_str));
 
-	while (tmp_str[0]) {
-		sub_str = strsep(&tmp_str, delimiter);
+	while ((sub_str = strsep(&tmp_str, delimiter)) != NULL) {
 		ret = kstrtol(sub_str, 0, &parameter[parameter_size]);
 		if (ret)
 			return -EINVAL;
@@ -1036,8 +1035,7 @@ static ssize_t amdgpu_read_mask(const ch
 	memcpy(buf_cpy, buf, bytes);
 	buf_cpy[bytes] = '\0';
 	tmp = buf_cpy;
-	while (tmp[0]) {
-		sub_str = strsep(&tmp, delimiter);
+	while ((sub_str = strsep(&tmp, delimiter)) != NULL) {
 		if (strlen(sub_str)) {
 			ret = kstrtol(sub_str, 0, &level);
 			if (ret)
@@ -1634,8 +1632,7 @@ static ssize_t amdgpu_set_pp_power_profi
 			i++;
 		memcpy(buf_cpy, buf, count-i);
 		tmp_str = buf_cpy;
-		while (tmp_str[0]) {
-			sub_str = strsep(&tmp_str, delimiter);
+		while ((sub_str = strsep(&tmp_str, delimiter)) != NULL) {
 			ret = kstrtol(sub_str, 0, &parameter[parameter_size]);
 			if (ret)
 				return -EINVAL;