[Mesa-dev] [PATCH 1/5] st/glsl_to_tgsi: fix a use-after-free in merge_two_dsts

[Nicolai Hähnle]

From: Nicolai Hähnle <nicolai.haehnle at amd.com>

Found by address sanitizer.

The loop here tries to be safe, but in doing so, it ends up doing
exactly the wrong thing: the safe foreach is for when the loop
variable (inst) could be deleted and nothing else. However, this
particular can delete inst's successor, but not inst itself.

Fixes: 8c6a0ebaad72 ("st/mesa: add st fp64 support (v7.1)")
---
 src/mesa/state_tracker/st_glsl_to_tgsi.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
index 609920a7a87..f4870a1c606 100644
--- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
@@ -5141,21 +5141,22 @@ glsl_to_tgsi_visitor::eliminate_dead_code(void)
    ralloc_free(write_level);
    ralloc_free(writes);
 
    return removed;
 }
 
 /* merge DFRACEXP instructions into one. */
 void
 glsl_to_tgsi_visitor::merge_two_dsts(void)
 {
-   foreach_in_list_safe(glsl_to_tgsi_instruction, inst, &this->instructions) {
+   /* We never delete inst, but we may delete its successor. */
+   foreach_in_list(glsl_to_tgsi_instruction, inst, &this->instructions) {
       glsl_to_tgsi_instruction *inst2;
       bool merged;
       if (num_inst_dst_regs(inst) != 2)
          continue;
 
       if (inst->dst[0].file != PROGRAM_UNDEFINED &&
           inst->dst[1].file != PROGRAM_UNDEFINED)
          continue;
 
       inst2 = (glsl_to_tgsi_instruction *) inst->next;
-- 
2.11.0