[PATCH v3 2/4] drm/nouveau/clk: don't use the pstate cursor after the loop

[Francesco Magazzu]

nvkm_pstate_prog() walks clk->states looking for the entry at index
'pstatei' and then keeps using the list_for_each_entry cursor after the
loop.  This is not triggerable today: every caller clamps the index
against clk->state_nr before calling, so the loop always breaks on a real
entry.  It is safe by virtue of what the callers happen to do, not by
anything the function itself checks.

Should a caller ever pass an index that is not on the list, the cursor
would point at the list head rather than at a pstate, and the
pstate->base.domain[] and pstate->fanspeed accesses that follow would read
past it.  Rather than leave that trap in place for the next caller, track
whether the entry was found and return -EINVAL if it was not.

No functional change.

Signed-off-by: Francesco Magazzu <postadelmaga@xxxxxxxxx>
Reviewed-by: Lyude Paul <lyude@xxxxxxxxxx>
---
 drivers/gpu/drm/nouveau/nvkm/subdev/clk/base.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/clk/base.c b/drivers/gpu/drm/nouveau/nvkm/subdev/clk/base.c
index 5da82db71..a43246ae6 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/clk/base.c
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/clk/base.c
@@ -270,13 +270,19 @@ nvkm_pstate_prog(struct nvkm_clk *clk, int pstatei)
 	struct nvkm_fb *fb = subdev->device->fb;
 	struct nvkm_pci *pci = subdev->device->pci;
 	struct nvkm_pstate *pstate;
+	bool found = false;
 	int ret, idx = 0;
 
 	list_for_each_entry(pstate, &clk->states, head) {
-		if (idx++ == pstatei)
+		if (idx++ == pstatei) {
+			found = true;
 			break;
+		}
 	}
 
+	if (!found)
+		return -EINVAL;
+
 	nvkm_debug(subdev, "setting performance state %d\n", pstatei);
 	clk->pstate = pstatei;
 
-- 
2.55.0