[PATCH v16 01/20] drm/shmem-helper: Fix UAF in error path when freeing SGT of imported GEM

[Dmitry Osipenko]

Freeing drm-shmem GEM right after creating it using
drm_gem_shmem_prime_import_sg_table() frees SGT of the imported dma-buf
and then dma-buf frees this SGT second time.

The v3d_prime_import_sg_table() is example of a error code path where
dma-buf's SGT is freed by drm-shmem and then it's freed second time by
dma_buf_unmap_attachment() in drm_gem_prime_import_dev().

Add drm-shmem GEM flag telling that this is imported SGT shall not be
treated as own SGT, fixing the use-after-free bug.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 2194a63a818d ("drm: Add library for shmem backed GEM objects")
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 13 ++++++++++++-
 include/drm/drm_gem_shmem_helper.h     |  7 +++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index e435f986cd13..6693d4061ca1 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -141,7 +141,7 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
 
 	if (obj->import_attach) {
 		drm_prime_gem_destroy(obj, shmem->sgt);
-	} else {
+	} else if (!shmem->imported_sgt) {
 		dma_resv_lock(shmem->base.resv, NULL);
 
 		drm_WARN_ON(obj->dev, shmem->vmap_use_count);
@@ -765,6 +765,17 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
 
 	shmem->sgt = sgt;
 
+	/*
+	 * drm_gem_shmem_prime_import_sg_table() can be called from a
+	 * driver specific ->import_sg_table() implementations that
+	 * may fail, in that case drm_gem_shmem_free() will be invoked
+	 * without assigned drm_gem_object::import_attach.
+	 *
+	 * This flag lets drm_gem_shmem_free() differentiate whether
+	 * SGT belongs to dmabuf and shall not be freed by drm-shmem.
+	 */
+	shmem->imported_sgt = true;
+
 	drm_dbg_prime(dev, "size = %zu\n", size);
 
 	return &shmem->base;
diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index bf0c31aa8fbe..ec70a98a8fe1 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -73,6 +73,13 @@ struct drm_gem_shmem_object {
 	 */
 	unsigned int vmap_use_count;
 
+	/**
+	 * @imported_sgt:
+	 *
+	 * True if SG table belongs to imported dma-buf.
+	 */
+	bool imported_sgt : 1;
+
 	/**
 	 * @pages_mark_dirty_on_put:
 	 *
-- 
2.41.0