On-list because the cat is out of the bag and we're clearly not good
enough to figure this out in private. The story thus far:
5e28b7b94408 ("drm: Set old handle to NULL before prime swap in
change_handle") tried to fix a race condition between the gem_close and
gem_change_handle ioctls, but got a few things wrong:
- There's a confusion with the local variable handle, which is actually
the new handle, and so the two-stage trick was actually applied to the
wrong idr slot. 7164d78559b0 ("drm/gem: fix race between
change_handle and handle_delete") tried to fix that by adding yet
another code block, but forgot to add the error handling. Which meant
we now have two paths, both kinda wrong.
- dc366607c41c ("drm: Replace old pointer to new idr") tried to apply
another fix, but inconsistently, again because of the handle confusion
- this would be the right fix (kinda, somewhat, it's a mess) if we'd
do the two-stage approach for the new handle. Except that wasn't the
intent of the original fix.
We also didn't have an igt merged for the original ioctl, which is a big
no-go. This was attempted to address off-list in the original bugfix,
and amd QA people claimed the bug was fixed now. Very clearly that's not
the case. Here's my attempt to sort this out:
- Rename the local variable to new_handle, the old aliasing with
args->handle is just too dangerously confusing.
- Merge the gem obj lookup with the two-stage idr_replace so that we
avoid getting ourselves confused there.
- This means we don't have a surplus temporary reference anymore, only
an inherited from the idr. A concurrent gem_close on the new_handle
could steal that. Fix that with the same two-stage approach
create_tail uses. This is a bit overkill as documented in the comment,
but I also don't trust my ability to understand this all correctly, so
go with the established pattern we have from other ioctls instead for
maximum paranoia.
- Adjust error paths. I've tried to make the error and success paths
common, because they are identical except for which handle is removed
and on which we call idr_replace to (re)install the object again. But
that made things messier to read, so I've left it at the more verbose
version, which unfortunately hides the symmetry in the entire code
flow a bit.
- While at it, also replace the 7 space indent with 1 tab.
And finally, because I flat out don't trust my abilities here at all
anymore:
- Disable the ioctl until we have the igt situation and everything else
sorted out on-list and with full consensus.
v2:
Sashiko noticed that I didn't handle the error path for idr_replace
correctly, it must be checked with IS_ERR_OR_NULL like in
gem_handle_delete. So yeah, definitely should just the existing paths
1:1 because this is endless amounts of tricky.
Also add the Fixes: line for the original ioctl, I forgot that too.
Reported-by: DARKNAVY (@DarkNavyOrg) <[email protected]>
Signed-off-by: Simona Vetter <[email protected]>
Fixes: dc366607c41c ("drm: Replace old pointer to new idr")
Cc: [email protected]
Cc: [email protected]
Cc: Edward Adam Davis <[email protected]>
Cc: Dave Airlie <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Maxime Ripard <[email protected]>
Cc: Thomas Zimmermann <[email protected]>
Fixes: 5e28b7b94408 ("drm: Set old handle to NULL before prime swap in
change_handle")
Cc: David Francis <[email protected]>
Cc: Puttimet Thammasaeng <[email protected]>
Cc: Christian Koenig <[email protected]>
Fixes: 7164d78559b0 ("drm/gem: fix race between change_handle and
handle_delete")
Cc: Zhenghang Xiao <[email protected]>
Fixes: 5e28b7b94408 ("drm: Set old handle to NULL before prime swap in
change_handle")
---
drivers/gpu/drm/drm_gem.c | 62 +++++++++++++------------------------
drivers/gpu/drm/drm_ioctl.c | 2 +-
2 files changed, 23 insertions(+), 41 deletions(-)
diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index e12cdf91f4dc..f49f1724eda5 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -1019,8 +1019,8 @@ int drm_gem_change_handle_ioctl(struct drm_device *dev,
void *data,
struct drm_file *file_priv)
{
struct drm_gem_change_handle *args = data;
- struct drm_gem_object *obj, *idrobj;
- int handle, ret;
+ struct drm_gem_object *obj;
+ int new_handle, ret;
if (!drm_core_check_feature(dev, DRIVER_GEM))
return -EOPNOTSUPP;
@@ -1028,52 +1028,36 @@ int drm_gem_change_handle_ioctl(struct drm_device *dev,
void *data,
/* idr_alloc() limitation. */
if (args->new_handle > INT_MAX)
return -EINVAL;
- handle = args->new_handle;
-
- obj = drm_gem_object_lookup(file_priv, args->handle);
- if (!obj)
- return -ENOENT;
+ new_handle = args->new_handle;
- if (args->handle == handle) {
- ret = 0;
- goto out;
- }
+ if (args->handle == new_handle)
+ return 0;
mutex_lock(&file_priv->prime.lock);
-
spin_lock(&file_priv->table_lock);
-
- /* When create_tail allocs an obj idr, it needs to first alloc as NULL,
- * then later replace with the correct object. This is not necessary
- * here, because the only operations that could race are drm_prime
- * bookkeeping, and we hold the prime lock.
- */
- ret = idr_alloc(&file_priv->object_idr, obj, handle, handle + 1,
+ ret = idr_alloc(&file_priv->object_idr, NULL, new_handle, new_handle +
1,
GFP_NOWAIT);
- if (ret < 0) {
- spin_unlock(&file_priv->table_lock);
- goto out_unlock;
- }
-
- idrobj = idr_replace(&file_priv->object_idr, NULL, handle);
- if (idrobj != obj) {
- idr_replace(&file_priv->object_idr, idrobj, handle);
- idr_remove(&file_priv->object_idr, args->new_handle);
- spin_unlock(&file_priv->table_lock);
- ret = -ENOENT;
- goto out_unlock;
- }
-
- idr_replace(&file_priv->object_idr, NULL, args->handle);
+ if (ret < 0) {
+ spin_unlock(&file_priv->table_lock);
+ goto out_unlock;
+ }
+
+ obj = idr_replace(&file_priv->object_idr, NULL, args->handle);
+ if (IS_ERR_OR_NULL(obj)) {
+ idr_remove(&file_priv->object_idr, new_handle);
+ spin_unlock(&file_priv->table_lock);
+ ret = -ENOENT;
+ goto out_unlock;
+ }
spin_unlock(&file_priv->table_lock);
if (obj->dma_buf) {
ret = drm_prime_add_buf_handle(&file_priv->prime, obj->dma_buf,
- handle);
+ new_handle);
if (ret < 0) {
spin_lock(&file_priv->table_lock);
- idr_remove(&file_priv->object_idr, handle);
+ idr_remove(&file_priv->object_idr, new_handle);
idr_replace(&file_priv->object_idr, obj, args->handle);
spin_unlock(&file_priv->table_lock);
goto out_unlock;
@@ -1086,14 +1070,12 @@ int drm_gem_change_handle_ioctl(struct drm_device *dev,
void *data,
spin_lock(&file_priv->table_lock);
idr_remove(&file_priv->object_idr, args->handle);
- idrobj = idr_replace(&file_priv->object_idr, obj, handle);
+ obj = idr_replace(&file_priv->object_idr, obj, new_handle);
spin_unlock(&file_priv->table_lock);
- WARN_ON(idrobj != NULL);
+ WARN_ON(obj != NULL);
out_unlock:
mutex_unlock(&file_priv->prime.lock);
-out:
- drm_gem_object_put(obj);
return ret;
}
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index ff193155129e..937fc1e2c017 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -660,7 +660,7 @@ static const struct drm_ioctl_desc drm_ioctls[] = {
DRM_IOCTL_DEF(DRM_IOCTL_GEM_CLOSE, drm_gem_close_ioctl,
DRM_RENDER_ALLOW),
DRM_IOCTL_DEF(DRM_IOCTL_GEM_FLINK, drm_gem_flink_ioctl, DRM_AUTH),
DRM_IOCTL_DEF(DRM_IOCTL_GEM_OPEN, drm_gem_open_ioctl, DRM_AUTH),
- DRM_IOCTL_DEF(DRM_IOCTL_GEM_CHANGE_HANDLE, drm_gem_change_handle_ioctl,
DRM_RENDER_ALLOW),
+ DRM_IOCTL_DEF(DRM_IOCTL_GEM_CHANGE_HANDLE, drm_invalid_op,
DRM_RENDER_ALLOW),
DRM_IOCTL_DEF(DRM_IOCTL_MODE_GETRESOURCES, drm_mode_getresources, 0),
--
2.53.0
