drm/crtc: Fix uninit-value bug in drm_mode_setcrtc

[ 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@syzkaller.appspotmail.com
Signed-off-by: Ziqi Zhao <astrajoan@yahoo.com>
Reported-and-tested-by: syzbot+4fad2e57beb6397ab2fc@syzkaller.appspotmail.com
Tested-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Link: https://lore.kernel.org/r/20230721161446.8602-1-astrajoan@yahoo.com
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index df9bf3c9206e717bdb7409ee0c99574df947ed0b..d718c17ab1e9f7edbd85423e94288d63a41044cb 100644 (file)
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -715,8 +715,7 @@ 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 -EOPNOTSUPP;
@@ -851,6 +850,7 @@ 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;
@@ -871,6 +871,7 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
                                        connector->name);
 
                        connector_set[i] = connector;
+                       num_connectors++;
                }
        }
 
@@ -879,7 +880,7 @@ 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;
 
        if (drm_drv_uses_atomic_modeset(dev))
@@ -892,7 +893,7 @@ out:
                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]);
                }