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 --- 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 df9bf3c9206e..d718c17ab1e9 100644 --- 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 @@ 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]); }