[PATCH] drm/amdgpu: fix lock leak on ENOMEM in AMDGPU_GEM_OP_GET_MAPPING_INFO

[Michael Bommarito <michael.bommarito@gmail.com>]

The AMDGPU_GEM_OP_GET_MAPPING_INFO branch of amdgpu_gem_op_ioctl()
holds three cleanup-tracked resources before calling kvcalloc():
the drm_gem_object reference from drm_gem_object_lookup(), the
drm_exec lock on the looked-up GEM via drm_exec_lock_obj(), and
the drm_exec lock on the per-process VM root page directory via
amdgpu_vm_lock_pd().  All three are released by the out_exec
label that every other error path in this function jumps to.
The kvcalloc() failure path returns -ENOMEM directly, skipping
out_exec and leaking all three.

The leaked per-process VM root PD dma_resv lock is the
load-bearing leak: any subsequent operation on the same VM
(further GEM ops, command-submission, eviction, TTM shrinker
callbacks) blocks on the held lock.  DRM_IOCTL_AMDGPU_GEM_OP is
DRM_AUTH | DRM_RENDER_ALLOW, so this is an unprivileged-local
denial of service against the caller's GPU context, reachable
by any process with /dev/dri/renderD* access.

Route the failure through out_exec so drm_exec_fini() and
drm_gem_object_put() run.

Reproduced on stock 7.0.0-10, Ryzen 7 5700U / Radeon Vega
(Lucienne): the failing ioctl returns -ENOMEM and a second
GET_MAPPING_INFO on the same fd then blocks in
drm_exec_lock_obj() on the leaked dma_resv.  SIGKILL on the
caller does not reap the task; the fd-release path during
process exit goes through amdgpu_gem_object_close() ->
drm_exec_prepare_obj() on the same lock, leaving the task in D
state until the box is rebooted.  The patched kernel was not
rebuilt and re-tested on this hardware; the fix is mechanical.
Tested on a single Lucienne / Vega box only.

Ziyi Guo posted an independent INT_MAX-bound check for
args->num_entries in the same branch [1]; the two patches are
complementary and can land in either order.

Fixes: 4d82724f7f2b ("drm/amdgpu: Add mapping info option for GEM_OP ioctl")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20260208000255.4073363-1-n7l8m4@u.northwestern.edu/ # [1]
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Assisted-by: Claude:claude-opus-4-7
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
index 9ef80bca4102..8224fb499fdf 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
@@ -1091,8 +1091,10 @@ int amdgpu_gem_op_ioctl(struct drm_device *dev, void *data,
 		 * be retried.
 		 */
 		vm_entries = kvcalloc(args->num_entries, sizeof(*vm_entries), GFP_KERNEL);
-		if (!vm_entries)
-			return -ENOMEM;
+		if (!vm_entries) {
+			r = -ENOMEM;
+			goto out_exec;
+		}
 
 		amdgpu_vm_bo_va_for_each_valid_mapping(bo_va, mapping) {
 			if (num_mappings < args->num_entries) {
-- 
2.53.0