FAILED: patch "[PATCH] drm/nouveau/svm: drain fault handler before freeing svmm" failed to apply to 6.1-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x b46ddaf0823405f81e681eb26ec98508f3eb9a07
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107054047-failed-6.1-b46ddaf08234@kernel.org' --subject-prefix 'PATCH 6.1.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From b46ddaf0823405f81e681eb26ec98508f3eb9a07 Mon Sep 17 00:00:00 2001
From: Zhenhao Wan <whi4ed0g@gmail.com>
Date: Fri, 14 Aug 2026 18:00:05 +0800
Subject: [PATCH] drm/nouveau/svm: drain fault handler before freeing svmm

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 <danisjiang@gmail.com>
Assisted-by: Claude:claude-opus-5
Cc: stable@vger.kernel.org
Signed-off-by: Zhenhao Wan <whi4ed0g@gmail.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patch.msgid.link/20260814-nouveau-svm-svmm-uaf-v2-1-8e6590519f07@gmail.com
---
 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 dcc92131488ea..a87406d3da300 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