st/theme-node: Fix potential NULL pointer dereferences

If the new CSS functions added in commit c593aecbde3
are used wrongly, an expected argument may be missing.

The code checks for that, but only after dereferencing
it to assign the next argument. Fix that by splitting
up the checks.

Spotted by coverity.
CID: #462818
Fixes: c593aecbde ("st/theme-node: Implement extensions for accent
color")

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3380>

diff --git a/src/st/st-theme-node.c b/src/st/st-theme-node.c
index 9ea539e31fe8ea25f4ea6e42c03fefd72dc3788a..0817e51fc78ed16ab266ac78017da316123298d4 100644 (file)
--- a/src/st/st-theme-node.c
+++ b/src/st/st-theme-node.c
@@ -617,13 +617,17 @@ get_color_from_transparentize_term (StThemeNode *node,
                                     CRTerm      *term,
                                     CoglColor   *color)
 {
-  CRTerm *color_arg = term->ext_content.func_param;
-  CRTerm *amount_arg = color_arg->next;
+  CRTerm *color_arg, *amount_arg;
   CoglColor base_color;
   CRNum *amount_num;
   double amount;
 
-  if (!color_arg || !amount_arg)
+  color_arg = term->ext_content.func_param;
+  if (!color_arg)
+    return VALUE_NOT_FOUND;
+
+  amount_arg = color_arg->next;
+  if (!amount_arg)
     return VALUE_NOT_FOUND;
 
   if (get_color_from_term (node, color_arg, &base_color) != VALUE_FOUND)
@@ -656,14 +660,21 @@ get_color_from_mix_term (StThemeNode *node,
                          CRTerm      *term,
                          CoglColor   *color)
 {
-  CRTerm *color1_arg = term->ext_content.func_param;
-  CRTerm *color2_arg = color1_arg->next;
-  CRTerm *factor_arg = color2_arg->next;
+  CRTerm *color1_arg, *color2_arg, *factor_arg;
   CoglColor color1, color2;
   CRNum *factor_num;
   double factor;
 
-  if (!color1_arg || !color2_arg || !factor_arg)
+  color1_arg = term->ext_content.func_param;
+  if (!color1_arg)
+    return VALUE_NOT_FOUND;
+
+  color2_arg = color1_arg->next;
+  if (!color2_arg)
+    return VALUE_NOT_FOUND;
+
+  factor_arg = color2_arg->next;
+  if (!factor_arg)
     return VALUE_NOT_FOUND;
 
   if (get_color_from_term (node, color1_arg, &color1) != VALUE_FOUND ||
@@ -706,14 +717,18 @@ get_color_from_lighten_term (StThemeNode *node,
                              CRTerm      *term,
                              CoglColor   *color)
 {
-  CRTerm *color_arg = term->ext_content.func_param;
-  CRTerm *factor_arg = color_arg->next;
+  CRTerm *color_arg, *factor_arg;
   CoglColor base_color;
   CRNum *factor_num;
   double factor;
   float hue, luminance, saturation;
 
-  if (!color_arg || !factor_arg)
+  color_arg = term->ext_content.func_param;
+  if (!color_arg)
+    return VALUE_NOT_FOUND;
+
+  factor_arg = color_arg->next;
+  if (!factor_arg)
     return VALUE_NOT_FOUND;
 
   if (get_color_from_term (node, color_arg, &base_color) != VALUE_FOUND)
@@ -746,14 +761,18 @@ get_color_from_darken_term (StThemeNode *node,
                             CRTerm      *term,
                             CoglColor   *color)
 {
-  CRTerm *color_arg = term->ext_content.func_param;
-  CRTerm *factor_arg = color_arg->next;
+  CRTerm *color_arg, *factor_arg;
   CoglColor base_color;
   CRNum *factor_num;
   double factor;
   float hue, luminance, saturation;
 
-  if (!color_arg || !factor_arg)
+  color_arg = term->ext_content.func_param;
+  if (!color_arg)
+    return VALUE_NOT_FOUND;
+
+  factor_arg = color_arg->next;
+  if (!factor_arg)
     return VALUE_NOT_FOUND;
 
   if (get_color_from_term (node, color_arg, &base_color) != VALUE_FOUND)