6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Zhenhao Wan [ Upstream commit b46ddaf0823405f81e681eb26ec98508f3eb9a07 ] The SVM fault handler nouveau_svm_fault() looks up each fault's nouveau_svmm under svm->mutex, caches it in the fault array, then drops svm->mutex and dereferences the svmm across blocking faults (mmu_interval_notifier_insert(), hmm_range_fault()). nouveau_svmm is not refcounted. On DRM file close nouveau_svmm_fini() -> mmu_notifier_put() frees it asynchronously via call_srcu() without waiting for the handler, and mmget_not_zero() pins the mm, not the svmm. flush_work() on the fault buffer otherwise runs only at device removal and suspend, never on close, so a fault handled concurrently with a close can dereference a freed svmm. The instance is already unlinked by nouveau_svmm_part() earlier in the same close, so no new fault can resolve to it. Drain the handler in nouveau_svmm_fini() before the free, guarding the flush with a NULL check on drm->svm: on device teardown nouveau_svm_fini() runs first and frees drm->svm (NULL) after blocking the notify and flushing the buffer, so the handler is already drained; on per-client close drm->svm is alive and the flush runs. Fixes: eeaf06ac1a55 ("drm/nouveau/svm: initial support for shared virtual memory") Reported-by: Yuhao Jiang Assisted-by: Claude:claude-opus-5 Cc: stable@vger.kernel.org Signed-off-by: Zhenhao Wan Reviewed-by: Lyude Paul Signed-off-by: Lyude Paul Link: https://patch.msgid.link/20260814-nouveau-svm-svmm-uaf-v2-1-8e6590519f07@gmail.com Signed-off-by: Sasha Levin --- drivers/gpu/drm/nouveau/nouveau_svm.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c b/drivers/gpu/drm/nouveau/nouveau_svm.c index 6fa387da06371..dc6c79f57a56d 100644 --- a/drivers/gpu/drm/nouveau/nouveau_svm.c +++ b/drivers/gpu/drm/nouveau/nouveau_svm.c @@ -304,6 +304,19 @@ nouveau_svmm_fini(struct nouveau_svmm **psvmm) { struct nouveau_svmm *svmm = *psvmm; if (svmm) { + struct nouveau_svm *svm = svmm->vmm->cli->drm->svm; + + /* The fault handler caches svmm pointers under svm->mutex and + * dereferences them after dropping it, across blocking faults. + * The instance is already unlinked (nouveau_svmm_part), so drain + * the handler before the free to release any in-flight reference. + * + * On device teardown nouveau_svm_fini() ran first and freed + * drm->svm (NULL) after draining the buffer; nothing to flush. + */ + if (svm) + flush_work(&svm->buffer[0].work); + mutex_lock(&svmm->mutex); svmm->vmm = NULL; mutex_unlock(&svmm->mutex); -- 2.53.0