[PATCH v2 2/3] drm/nouveau/uvmm: fix premature region free on failed OP_UNMAP_SPARSE

[Zhenhao Wan]

In nouveau_uvmm_bind_job_submit()'s OP_UNMAP_SPARSE arm, op->reg is set
from nouveau_uvma_region_find(), which only looks the region up and takes
no reference; a region's sole reference is its membership in
uvmm->region_mt. Two failure paths leave op->reg set: the -ENOENT check
when the region is busy, and the drm_gpuvm_sm_unmap_ops_create() failure.
The sibling nouveau_uvmm_sm_unmap_prepare() failure just below clears
op->reg; these two do not.

unwind_continue steps back one op, so the failing op is skipped by the
unwind loop and its op->reg stays set. nouveau_uvmm_bind_job_cleanup()
then enters its if (op->reg) branch and calls nouveau_uvma_region_remove()
and nouveau_uvma_region_put() on it, dropping the tree's sole reference
and freeing a region this job never created. The comment above the
cleanup loop documents the broken invariant: op->reg must be NULL on
submit failure.

This frees a live region on an unrelated failure, reachable single-job
when drm_gpuvm_sm_unmap_ops_create() returns -ENOMEM; if another job owns
the same region, its cleanup then removes and puts the freed region, a
use-after-free. Clear op->reg on both failure paths.

Fixes: b88baab82871 ("drm/nouveau: implement new VM_BIND uAPI")
Reported-by: Yuhao Jiang <danisjiang@xxxxxxxxx>
Assisted-by: Claude:claude-opus-5
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Zhenhao Wan <whi4ed0g@xxxxxxxxx>
---
 drivers/gpu/drm/nouveau/nouveau_uvmm.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/nouveau_uvmm.c b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
index 849bf42c124e..3412200b21fd 100644
--- a/drivers/gpu/drm/nouveau/nouveau_uvmm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_uvmm.c
@@ -1319,6 +1319,7 @@ nouveau_uvmm_bind_job_submit(struct nouveau_job *job,
 							   op->va.range);
 			if (!op->reg || op->reg->dirty) {
 				ret = -ENOENT;
+				op->reg = NULL;
 				goto unwind_continue;
 			}
 
@@ -1327,6 +1328,7 @@ nouveau_uvmm_bind_job_submit(struct nouveau_job *job,
 								op->va.range);
 			if (IS_ERR(op->ops)) {
 				ret = PTR_ERR(op->ops);
+				op->reg = NULL;
 				goto unwind_continue;
 			}
 

-- 
2.34.1