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Fri, 28 Aug 2026 07:58:06 -0700 (PDT) From: "Jonghyuk Kim(MalHyuk)" To: Matthew Brost , Danilo Krummrich , Philipp Stanner Cc: =?UTF-8?q?Christian=20K=C3=B6nig?= , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, "Jonghyuk Kim(MalHyuk)" Subject: [PATCH v1 1/2] drm/sched: cache the timeline name to fix a use-after-free Date: Fri, 28 Aug 2026 23:57:56 +0900 Message-ID: X-Mailer: git-send-email 2.43.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit drm_sched_fence_get_timeline_name() returns fence->sched->name, and the drm_sched_fence ops keep a .release callback, so the fence is not ops-detached on signalling (dma_fence_signal_timestamp_locked() only clears ->ops for fences without .release/.wait). The callback therefore stays reachable on a long-signalled, userspace-held finished fence and unconditionally dereferences fence->sched. A driver that allocates a drm_gpu_scheduler at per-context/per-queue/ per-VM granularity and frees it on an unprivileged context/fd close, while exporting the resulting finished fence to userspace (drm_syncobj / sync_file / dma_resv), leaves fence->sched dangling after the free. A subsequent SYNC_IOC_FILE_INFO ioctl (which calls get_timeline_name()) then reads the freed scheduler: BUG: KASAN: slab-use-after-free in drm_sched_fence_get_timeline_name This is the same class as CVE-2025-38703 (drm/xe) and CVE-2025-71302 (drm/panthor), which were fixed per-driver. amdxdna, nouveau and msm (VM_BIND) are still affected in mainline, so fix it in the core to cover any per-context-scheduler driver at once. Scheduler names are persistent strings (string literals passed to drm_sched_init()), so cache the name pointer in the fence at init time, while the scheduler is guaranteed alive, and return the cached value from get_timeline_name() without dereferencing fence->sched. Signed-off-by: Jonghyuk Kim(MalHyuk) --- drivers/gpu/drm/scheduler/sched_fence.c | 16 +++++++++++++++- include/drm/gpu_scheduler.h | 11 +++++++++++ 2 files changed, 26 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/scheduler/sched_fence.c b/drivers/gpu/drm/scheduler/sched_fence.c index 85ee3d694dc9..280a2d036ffd 100644 --- a/drivers/gpu/drm/scheduler/sched_fence.c +++ b/drivers/gpu/drm/scheduler/sched_fence.c @@ -92,7 +92,13 @@ static const char *drm_sched_fence_get_driver_name(struct dma_fence *fence) static const char *drm_sched_fence_get_timeline_name(struct dma_fence *f) { struct drm_sched_fence *fence = to_drm_sched_fence(f); - return (const char *)fence->sched->name; + + /* + * Do not dereference fence->sched here: a userspace-held finished + * fence can outlive a per-context scheduler. Return the name cached + * in drm_sched_fence_init() instead. + */ + return fence->sched_name; } static void drm_sched_fence_free_rcu(struct rcu_head *rcu) @@ -228,6 +234,14 @@ void drm_sched_fence_init(struct drm_sched_fence *fence, unsigned seq; fence->sched = container_of(entity->rq, typeof(*fence->sched), rq); + /* + * Cache the scheduler's timeline name: the finished fence may be + * exported to userspace and outlive @sched (per-context schedulers + * are freed on context teardown), so get_timeline_name() must not + * dereference @sched. Scheduler names are persistent (string + * literals passed to drm_sched_init()). + */ + fence->sched_name = fence->sched->name; seq = atomic_inc_return(&entity->fence_seq); dma_fence_init(&fence->scheduled, &drm_sched_fence_ops_scheduled, &fence->lock, entity->fence_context, seq); diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h index d61c19e78182..4f780d70acb6 100644 --- a/include/drm/gpu_scheduler.h +++ b/include/drm/gpu_scheduler.h @@ -305,6 +305,17 @@ struct drm_sched_fence { * belongs to. */ struct drm_gpu_scheduler *sched; + /** + * @sched_name: the timeline name of @sched, cached at init time. + * + * &drm_sched_fence.finished may be exported to userspace (via a + * sync_file or drm_syncobj) and can outlive @sched: a driver using a + * per-context scheduler frees it on context teardown while a + * userspace-held finished fence still references it. The + * get_timeline_name() callback must therefore not dereference @sched; + * it returns this cached name instead. + */ + const char *sched_name; /** * @lock: the lock used by the scheduled and the finished fences. */ -- 2.43.0