CVE-2022-50214 — coresight: Clear the connection field properly

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

coresight: Clear the connection field properly

coresight devices track their connections (output connections) and hold a reference to the fwnode. When a device goes away, we walk through the devices on the coresight bus and make sure that the references are dropped. This happens both ways: a) For all output connections from the device, drop the reference to the target device via coresight_release_platform_data()

b) Iterate over all the devices on the coresight bus and drop the reference to fwnode if *this* device is the target of the output connection, via coresight_remove_conns()->coresight_remove_match().

However, the coresight_remove_match() doesn't clear the fwnode field, after dropping the reference, this causes use-after-free and additional refcount drops on the fwnode.

e.g., if we have two devices, A and B, with a connection, A -> B. If we remove B first, B would clear the reference on B, from A via coresight_remove_match(). But when A is removed, it still has a connection with fwnode still pointing to B. Thus it tries to drops the reference in coresight_release_platform_data(), raising the bells like :

[ 91.990153] ------------[ cut here ]------------ [ 91.990163] refcount_t: addition on 0; use-after-free. [ 91.990212] WARNING: CPU: 0 PID: 461 at lib/refcount.c:25 refcount_warn_saturate+0xa0/0x144 [ 91.990260] Modules linked in: coresight_funnel coresight_replicator coresigh…

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CVE-2022-50214 — coresight: Clear the connection field properly