[Mesa-dev] [PATCH v2] glsl: fix heap-use-after-free in ast_declarator_list::hir()

[Samuel Iglesias Gonsálvez]

The get_variable_being_redeclared() function can free 'var' because
a re-declaration of an unsized array variable can establish the size, so
we set the array type to the 'earlier' declaration and free 'var' as it is
not needed anymore.

However, the same 'var' is referenced later in ast_declarator_list::hir().

This patch fixes it by assign the pointer 'var' to the pointer 'earlier'.

This error was detected by Address Sanitizer.

v2:

* Pointer-to-pointer assignment (Bartosz Tomczyk)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99677
Signed-off-by: Samuel Iglesias Gonsálvez <siglesias at igalia.com>
---

Another possibility is to use reference-to-pointer but it is a C++
thing. IIRC, we agreed on avoiding C++-specific features to make it
easy for C developers, but I have no strong opinion for either option.

 src/compiler/glsl/ast_to_hir.cpp | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/compiler/glsl/ast_to_hir.cpp b/src/compiler/glsl/ast_to_hir.cpp
index b31b61d1ed6..93ba1d510fa 100644
--- a/src/compiler/glsl/ast_to_hir.cpp
+++ b/src/compiler/glsl/ast_to_hir.cpp
@@ -3958,10 +3958,12 @@ apply_type_qualifier_to_variable(const struct ast_type_qualifier *qual,
  * is a redeclaration, \c NULL otherwise.
  */
 static ir_variable *
-get_variable_being_redeclared(ir_variable *var, YYLTYPE loc,
+get_variable_being_redeclared(ir_variable **var_pointer, YYLTYPE loc,
                               struct _mesa_glsl_parse_state *state,
                               bool allow_all_redeclarations)
 {
+   ir_variable *var = *var_pointer;
+
    /* Check if this declaration is actually a re-declaration, either to
     * resize an array or add qualifiers to an existing variable.
     *
@@ -3999,7 +4001,7 @@ get_variable_being_redeclared(ir_variable *var, YYLTYPE loc,
 
       earlier->type = var->type;
       delete var;
-      var = NULL;
+      *var_pointer = earlier;
    } else if ((state->ARB_fragment_coord_conventions_enable ||
               state->is_version(150, 0))
               && strcmp(var->name, "gl_FragCoord") == 0
@@ -5207,7 +5209,7 @@ ast_declarator_list::hir(exec_list *instructions,
       bool var_is_gl_id = is_gl_identifier(var->name);
 
       ir_variable *earlier =
-         get_variable_being_redeclared(var, decl->get_location(), state,
+         get_variable_being_redeclared(&var, decl->get_location(), state,
                                        false /* allow_all_redeclarations */);
       if (earlier != NULL) {
          if (var_is_gl_id &&
@@ -7873,7 +7875,7 @@ ast_interface_block::hir(exec_list *instructions,
 
          if (redeclaring_per_vertex) {
             ir_variable *earlier =
-               get_variable_being_redeclared(var, loc, state,
+               get_variable_being_redeclared(&var, loc, state,
                                              true /* allow_all_redeclarations */);
             if (!var_is_gl_id || earlier == NULL) {
                _mesa_glsl_error(&loc, state,
-- 
2.11.0