[PATCH 2/2] drm/nouveau: Fix NULL pointer dereference in GET_ZCULL_INFO ioctl

[Jim Cromie <jim.cromie@gmail.com>]

When graphics engine firmware fails to load or initialization aborts
early, nvxx_gr(drm) returns NULL. Calling DRM_IOCTL_NOUVEAU_GET_ZCULL_INFO
causes nouveau_abi16_ioctl_get_zcull_info() to dereference gr at offset
0xf0 without checking for NULL, triggering a kernel page fault.

Validate that gr is non-NULL before inspecting gr->has_zcull_info.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
Aug 14 09:21:52 frodo kernel: BUG: kernel NULL pointer dereference, address: 00000000000000f0
Aug 14 09:21:52 frodo kernel: #PF: error_code(0x0000) - not-present page
Aug 14 09:21:52 frodo kernel: Oops: Oops: 0000 [#1] SMP NOPTI
Aug 14 09:21:52 frodo kernel: RIP: 0010:nouveau_abi16_ioctl_get_zcull_info+0x17/0xa0 [nouveau]
Aug 14 09:21:52 frodo kernel: Code: 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 48 8b 47 40 48 8b 00 48 8b 80 70 02 00 00 <80> b8 f0 00 00 00 00 74 72 8b 90 c0 00 00 00 89 16 8b 90 c4 00 00
Aug 14 09:21:52 frodo kernel: Call Trace:
Aug 14 09:21:52 frodo kernel:  <TASK>
Aug 14 09:21:52 frodo kernel:  drm_ioctl_kernel+0xae/0x100
Aug 14 09:21:52 frodo kernel:  drm_ioctl+0x2e0/0x560
Aug 14 09:21:52 frodo kernel:  ? __pfx_nouveau_abi16_ioctl_get_zcull_info+0x10/0x10 [nouveau]
Aug 14 09:21:52 frodo kernel:  nouveau_drm_ioctl+0x58/0xc0 [nouveau]
Aug 14 09:21:52 frodo kernel:  __x64_sys_ioctl+0xb9/0x100
Aug 14 09:21:52 frodo kernel:  do_syscall_64+0xe2/0x560
Aug 14 09:21:52 frodo kernel:  entry_SYSCALL_64_after_hwframe+0x76/0x7e
Aug 14 09:21:52 frodo kernel:  </TASK>
---
 drivers/gpu/drm/nouveau/nouveau_abi16.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_abi16.c b/drivers/gpu/drm/nouveau/nouveau_abi16.c
index c9270c5b0fac..f1026a716ff7 100644
--- a/drivers/gpu/drm/nouveau/nouveau_abi16.c
+++ b/drivers/gpu/drm/nouveau/nouveau_abi16.c
@@ -357,7 +357,7 @@ nouveau_abi16_ioctl_get_zcull_info(ABI16_IOCTL_ARGS)
 	struct nvkm_gr *gr = nvxx_gr(drm);
 	struct drm_nouveau_get_zcull_info *out = data;
 
-	if (gr->has_zcull_info) {
+	if (gr && gr->has_zcull_info) {
 		const struct nvkm_gr_zcull_info *i = &gr->zcull_info;
 
 		out->width_align_pixels = i->width_align_pixels;

-- 
2.55.0