Francisco Casas : vkd3d-shader: Return a valid pointer when count=0 in param allocator (ubsan).

[Alexandre Julliard]

Module: vkd3d
Branch: master
Commit: 5b7191280b7709d51b585c4f517e7ede763e01b5
URL:    https://gitlab.winehq.org/wine/vkd3d/-/commit/5b7191280b7709d51b585c4f517e7e...

Author: Francisco Casas <fcasas(a)codeweavers.com>
Date:   Mon May  6 16:51:36 2024 -0400

vkd3d-shader: Return a valid pointer when count=0 in param allocator (ubsan).

After compiling and linking with '-fsanitize=undefined' the following
error pops up in many tests:

    vkd3d_shader_main.c:2024:12: runtime error: member access within null pointer of type 'struct vkd3d_shader_param_node'

This happens in the scenario where shader_param_allocator_get() gets
called with 'count = 0' but no allocation has been made yet, so
allocator->current is NULL.

In this case the result of the function, given by:

    params = &allocator->current->param[allocator->index * allocator->stride];

is an invalid non-NULL pointer.

Functions like shader_sm4_read_instruction() may call
vsir_program_get_src_params() or vsir_program_get_dst_params() with 0
counts for various DCL_ instructions, as well as things like NOP,
ELSE, and SYNC.

We could avoid calling the functions in question with 0 counts, but it
doesn't seem worth the effort.

Alternatively, we could just return NULL on 'count == 0', but this is
also complicated because NULL is interpreted as a memory allocation
failure on the callers.

So we force allocation of the next node even if 'count = 0' when
allocator->current is NULL.

---

 libs/vkd3d-shader/vkd3d_shader_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libs/vkd3d-shader/vkd3d_shader_main.c b/libs/vkd3d-shader/vkd3d_shader_main.c
index a7b42217..18456480 100644
--- a/libs/vkd3d-shader/vkd3d_shader_main.c
+++ b/libs/vkd3d-shader/vkd3d_shader_main.c
@@ -2004,7 +2004,7 @@ void *shader_param_allocator_get(struct vkd3d_shader_param_allocator *allocator,
 {
     void *params;
 
-    if (count > allocator->count - allocator->index)
+    if (!allocator->current || count > allocator->count - allocator->index)
     {
         struct vkd3d_shader_param_node *next;