From f236a6bcf57605aa1e5ce0ea721a5a785b77417b Mon Sep 17 00:00:00 2001
From: Xiaomeng Tong <xiam0nd.tong@gmail.com>
Date: Sun, 27 Mar 2022 15:58:24 +0800
Subject: drm/nouveau/clk: Fix an incorrect NULL check on list iterator
Git-commit: 1c3b2a27def609473ed13b1cd668cb10deab49b4
Patch-mainline: v5.19-rc1
References: jsc#PED-1166 jsc#PED-1168 jsc#PED-1170 jsc#PED-1218 jsc#PED-1220 jsc#PED-1222 jsc#PED-1223 jsc#PED-1225

The bug is here:
	if (nvkm_cstate_valid(clk, cstate, max_volt, clk->temp))
		return cstate;

The list iterator value 'cstate' will *always* be set and non-NULL
by list_for_each_entry_from_reverse(), so it is incorrect to assume
that the iterator value will be unchanged if the list is empty or no
element is found (In fact, it will be a bogus pointer to an invalid
structure object containing the HEAD). Also it missed a NULL check
at callsite and may lead to invalid memory access after that.

To fix this bug, just return 'encoder' when found, otherwise return
NULL. And add the NULL check.

Cc: stable@vger.kernel.org
Fixes: 1f7f3d91ad38a ("drm/nouveau/clk: Respect voltage limits in nvkm_cstate_prog")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220327075824.11806-1-xiam0nd.tong@gmail.com
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
 drivers/gpu/drm/nouveau/nvkm/subdev/clk/base.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/clk/base.c b/drivers/gpu/drm/nouveau/nvkm/subdev/clk/base.c
index 57199be082fd..c2b5cc5f97ed 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/clk/base.c
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/clk/base.c
@@ -135,10 +135,10 @@ nvkm_cstate_find_best(struct nvkm_clk *clk, struct nvkm_pstate *pstate,
 
 	list_for_each_entry_from_reverse(cstate, &pstate->list, head) {
 		if (nvkm_cstate_valid(clk, cstate, max_volt, clk->temp))
-			break;
+			return cstate;
 	}
 
-	return cstate;
+	return NULL;
 }
 
 static struct nvkm_cstate *
@@ -169,6 +169,8 @@ nvkm_cstate_prog(struct nvkm_clk *clk, struct nvkm_pstate *pstate, int cstatei)
 	if (!list_empty(&pstate->list)) {
 		cstate = nvkm_cstate_get(clk, pstate, cstatei);
 		cstate = nvkm_cstate_find_best(clk, pstate, cstate);
+		if (!cstate)
+			return -EINVAL;
 	} else {
 		cstate = &pstate->base;
 	}
-- 
2.38.1