Overview
About vulnerability
In the Linux kernel, the following vulnerability has been resolved:
net: dsa: mxl862xx: fix use-after-free of DSA ports in crc_err_work
Upon an MDIO CRC error mxl862xx_crc_err_work_fn() walks the DSA ports and closes the CPU port conduits:
dsa_switch_for_each_cpu_port(dp, priv->ds) dev_close(dp->conduit);
mxl862xx_remove() unregisters the switch before cancelling this work:
set_bit(MXL862XX_FLAG_WORK_STOPPED, &priv->flags); cancel_delayed_work_sync(&priv->stats_work); dsa_unregister_switch(ds); mxl862xx_host_shutdown(priv);
dsa_unregister_switch() frees the dsa_port objects. If a CRC error schedules the work during teardown it can run after the ports have been freed and dereference freed memory.
Guard the port walk with MXL862XX_FLAG_WORK_STOPPED, which is already set before dsa_unregister_switch(). DSA tears the ports down under rtnl_lock(), so checking the flag under rtnl_lock() means the work either runs before teardown and sees valid ports, or runs afterwards, observes the flag and skips the walk. This mirrors the host_flood_work handler, which skips torn-down ports under rtnl_lock().
Details
- Affected product:
- Debian 10 ELS
- Affected packages:
- linux @ 4.19.0