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binder: remove "invalid inc weak" check

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There are no scenarios where a weak increment is invalid on binder_node.
The only possible case where it could be invalid is if the kernel
delivers BR_DECREFS to the process that owns the node, and then
increments the weak refcount again, effectively "reviving" a dead node.

However, that is not possible: when the BR_DECREFS command is delivered,
the kernel removes and frees the binder_node. The fact that you were
able to call binder_inc_node_nilocked() implies that the node is not yet
destroyed, which implies that BR_DECREFS has not been delivered to
userspace, so incrementing the weak refcount is valid.

Note that it's currently possible to trigger this condition if the owner
calls BINDER_THREAD_EXIT while node->has_weak_ref is true. This causes
BC_INCREFS on binder_ref instances to fail when they should not.

Cc: stable@vger.kernel.org
Fixes: 457b9a6f09 ("Staging: android: add binder driver")
Reported-by: Yu-Ting Tseng <yutingtseng@google.com>
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20251015-binder-weak-inc-v1-1-7914b092c371@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Alice Ryhl
2025-10-15 14:26:55 +00:00
committed by Greg Kroah-Hartman
parent 2463ae285e
commit d90eeb8ecd
1 changed files with 1 additions and 10 deletions
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11
drivers/android/binder.c
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@@ -851,17 +851,8 @@ static int binder_inc_node_nilocked(struct binder_node *node, int strong,
} else {
if (!internal)
node->local_weak_refs++;
if (!node->has_weak_ref && list_empty(&node->work.entry)) {
if (target_list == NULL) {
pr_err("invalid inc weak node for %d\n",
node->debug_id);
return -EINVAL;
}
/*
* See comment above
*/
if (!node->has_weak_ref && target_list && list_empty(&node->work.entry))
binder_enqueue_work_ilocked(&node->work, target_list);
}
}
return 0;
}