Exynos Virtual Display driver performs memory allocation/free operations without lock protection, which easily causes concurrency problem.
For example, use-after-free can occur in race scenario like this: ``` CPU0 CPU1 CPU2 ---- ---- ---- vidi_connection_ioctl() if (vidi->connection) // true drm_edid = drm_edid_alloc(); // alloc drm_edid ... ctx->raw_edid = drm_edid; ... drm_mode_getconnector() drm_helper_probe_single_connector_modes() vidi_get_modes() if (ctx->raw_edid) // true drm_edid_dup(ctx->raw_edid); if (!drm_edid) // false ... vidi_connection_ioctl() if (vidi->connection) // false drm_edid_free(ctx->raw_edid); // free drm_edid ... drm_edid_alloc(drm_edid->edid) kmemdup(edid); // UAF!! ... ```
To prevent these vulns, at least in vidi_context, member variables related to memory alloc/free should be protected with ctx->lock.
Cc: stable@vger.kernel.org Signed-off-by: Jeongjun Park aha310510@gmail.com --- drivers/gpu/drm/exynos/exynos_drm_vidi.c | 38 ++++++++++++++++++++---- 1 file changed, 32 insertions(+), 6 deletions(-)
diff --git a/drivers/gpu/drm/exynos/exynos_drm_vidi.c b/drivers/gpu/drm/exynos/exynos_drm_vidi.c index 601406b640c7..37733f2ac0e7 100644 --- a/drivers/gpu/drm/exynos/exynos_drm_vidi.c +++ b/drivers/gpu/drm/exynos/exynos_drm_vidi.c @@ -186,29 +186,37 @@ static ssize_t vidi_store_connection(struct device *dev, const char *buf, size_t len) { struct vidi_context *ctx = dev_get_drvdata(dev); - int ret; + int ret, new_connected;
- ret = kstrtoint(buf, 0, &ctx->connected); + ret = kstrtoint(buf, 0, &new_connected); if (ret) return ret; - - if (ctx->connected > 1) + if (new_connected > 1) return -EINVAL;
+ mutex_lock(&ctx->lock); + /* * Use fake edid data for test. If raw_edid is set then it can't be * tested. */ if (ctx->raw_edid) { DRM_DEV_DEBUG_KMS(dev, "edid data is not fake data.\n"); - return -EINVAL; + ret = -EINVAL; + goto fail; }
+ ctx->connected = new_connected; + mutex_unlock(&ctx->lock); + DRM_DEV_DEBUG_KMS(dev, "requested connection.\n");
drm_helper_hpd_irq_event(ctx->drm_dev);
return len; +fail: + mutex_unlock(&ctx->lock); + return ret; }
static DEVICE_ATTR(connection, 0644, vidi_show_connection, @@ -243,11 +251,14 @@ int vidi_connection_ioctl(struct drm_device *drm_dev, void *data, return -EINVAL; }
+ mutex_lock(&ctx->lock); if (ctx->connected == vidi->connection) { + mutex_unlock(&ctx->lock); DRM_DEV_DEBUG_KMS(ctx->dev, "same connection request.\n"); return -EINVAL; } + mutex_unlock(&ctx->lock);
if (vidi->connection) { const struct drm_edid *drm_edid; @@ -281,14 +292,21 @@ int vidi_connection_ioctl(struct drm_device *drm_dev, void *data, "edid data is invalid.\n"); return -EINVAL; } + mutex_lock(&ctx->lock); ctx->raw_edid = drm_edid; + mutex_unlock(&ctx->lock); } else { /* with connection = 0, free raw_edid */ + mutex_lock(&ctx->lock); drm_edid_free(ctx->raw_edid); ctx->raw_edid = NULL; + mutex_unlock(&ctx->lock); }
+ mutex_lock(&ctx->lock); ctx->connected = vidi->connection; + mutex_unlock(&ctx->lock); + drm_helper_hpd_irq_event(ctx->drm_dev);
return 0; @@ -303,7 +321,7 @@ static enum drm_connector_status vidi_detect(struct drm_connector *connector, * connection request would come from user side * to do hotplug through specific ioctl. */ - return ctx->connected ? connector_status_connected : + return READ_ONCE(ctx->connected) ? connector_status_connected : connector_status_disconnected; }
@@ -326,11 +344,15 @@ static int vidi_get_modes(struct drm_connector *connector) const struct drm_edid *drm_edid; int count;
+ mutex_lock(&ctx->lock); + if (ctx->raw_edid) drm_edid = drm_edid_dup(ctx->raw_edid); else drm_edid = drm_edid_alloc(fake_edid_info, sizeof(fake_edid_info));
+ mutex_unlock(&ctx->lock); + drm_edid_connector_update(connector, drm_edid);
count = drm_edid_connector_add_modes(connector); @@ -482,9 +504,13 @@ static void vidi_remove(struct platform_device *pdev) { struct vidi_context *ctx = platform_get_drvdata(pdev);
+ mutex_lock(&ctx->lock); + drm_edid_free(ctx->raw_edid); ctx->raw_edid = NULL;
+ mutex_unlock(&ctx->lock); + component_del(&pdev->dev, &vidi_component_ops); }
--