linux-kernel - [PATCH AUTOSEL 4.14 3/6] drm/crtc: Fix uninit-value bug in drm_mode

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Date: Mon, 18 Dec 2023 07:47:20 -0500
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Ziqi Zhao <astrajoan@...oo.com>,
	syzbot+4fad2e57beb6397ab2fc@...kaller.appspotmail.com,
	Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>,
	Maxime Ripard <mripard@...nel.org>,
	Sasha Levin <sashal@...nel.org>,
	maarten.lankhorst@...ux.intel.com,
	tzimmermann@...e.de,
	airlied@...il.com,
	daniel@...ll.ch,
	dri-devel@...ts.freedesktop.org
Subject: [PATCH AUTOSEL 4.14 3/6] drm/crtc: Fix uninit-value bug in drm_mode_setcrtc

From: Ziqi Zhao <astrajoan@...oo.com>

[ Upstream commit 3823119b9c2b5f9e9b760336f75bc989b805cde6 ]

The connector_set contains uninitialized values when allocated with
kmalloc_array. However, in the "out" branch, the logic assumes that any
element in connector_set would be equal to NULL if failed to
initialize, which causes the bug reported by Syzbot. The fix is to use
an extra variable to keep track of how many connectors are initialized
indeed, and use that variable to decrease any refcounts in the "out"
branch.

Reported-by: syzbot+4fad2e57beb6397ab2fc@...kaller.appspotmail.com
Signed-off-by: Ziqi Zhao <astrajoan@...oo.com>
Reported-and-tested-by: syzbot+4fad2e57beb6397ab2fc@...kaller.appspotmail.com
Tested-by: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
Link: https://lore.kernel.org/r/20230721161446.8602-1-astrajoan@yahoo.com
Signed-off-by: Maxime Ripard <mripard@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/gpu/drm/drm_crtc.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 5af25ce5bf7c2..5ae3adfbc5e80 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -556,8 +556,7 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
 	struct drm_mode_set set;
 	uint32_t __user *set_connectors_ptr;
 	struct drm_modeset_acquire_ctx ctx;
-	int ret;
-	int i;
+	int ret, i, num_connectors;
 
 	if (!drm_core_check_feature(dev, DRIVER_MODESET))
 		return -EINVAL;
@@ -672,6 +671,7 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
 			goto out;
 		}
 
+		num_connectors = 0;
 		for (i = 0; i < crtc_req->count_connectors; i++) {
 			connector_set[i] = NULL;
 			set_connectors_ptr = (uint32_t __user *)(unsigned long)crtc_req->set_connectors_ptr;
@@ -692,6 +692,7 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
 					connector->name);
 
 			connector_set[i] = connector;
+			num_connectors++;
 		}
 	}
 
@@ -700,7 +701,7 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
 	set.y = crtc_req->y;
 	set.mode = mode;
 	set.connectors = connector_set;
-	set.num_connectors = crtc_req->count_connectors;
+	set.num_connectors = num_connectors;
 	set.fb = fb;
 	ret = __drm_mode_set_config_internal(&set, &ctx);
 
@@ -709,7 +710,7 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
 		drm_framebuffer_put(fb);
 
 	if (connector_set) {
-		for (i = 0; i < crtc_req->count_connectors; i++) {
+		for (i = 0; i < num_connectors; i++) {
 			if (connector_set[i])
 				drm_connector_put(connector_set[i]);
 		}
-- 
2.43.0