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

net: phy: register phy led_triggers during probe to avoid AB-BA deadlock

There is an AB-BA deadlock when both LEDS_TRIGGER_NETDEV and
LED_TRIGGER_PHY are enabled:

[ 1362.049207] [<8054e4b8>] led_trigger_register+0x5c/0x1fc <-- Trying to get lock "triggers_list_lock" via down_write(&triggers_list_lock);
[ 1362.054536] [<80662830>] phy_led_triggers_register+0xd0/0x234
[ 1362.060329] [<8065e200>] phy_attach_direct+0x33c/0x40c
[ 1362.065489] [<80651fc4>] phylink_fwnode_phy_connect+0x15c/0x23c
[ 1362.071480] [<8066ee18>] mtk_open+0x7c/0xba0
[ 1362.075849] [<806d714c>] __dev_open+0x280/0x2b0
[ 1362.080384] [<806d7668>] __dev_change_flags+0x244/0x24c
[ 1362.085598] [<806d7698>] dev_change_flags+0x28/0x78
[ 1362.090528] [<807150e4>] dev_ioctl+0x4c0/0x654 <-- Hold lock "rtnl_mutex" by calling rtnl_lock();
[ 1362.094985] [<80694360>] sock_ioctl+0x2f4/0x4e0
[ 1362.099567] [<802e9c4c>] sys_ioctl+0x32c/0xd8c
[ 1362.104022] [<80014504>] syscall_common+0x34/0x58

Here LED_TRIGGER_PHY is registering LED triggers during phy_attach
while holding RTNL and then taking triggers_list_lock.

[ 1362.191101] [<806c2640>] register_netdevice_notifier+0x60/0x168 <-- Trying to get lock "rtnl_mutex" via rtnl_lock();
[ 1362.197073] [<805504ac>] netdev_trig_activate+0x194/0x1e4
[ 1362.202490] [<8054e28c>] led_trigger_set+0x1d4/0x360 <-- Hold lock "triggers_list_lock" by down_read(&triggers_list_lock);
[ 1362.207511] [<8054eb38>] led_trigger_write+0xd8/0x14c
[ 1362.212566] [<80381d98>] sysfs_kf_bin_write+0x80/0xbc
[ 1362.217688] [<8037fcd8>] kernfs_fop_write_iter+0x17c/0x28c
[ 1362.223174] [<802cbd70>] vfs_write+0x21c/0x3c4
[ 1362.227712] [<802cc0c4>] ksys_write+0x78/0x12c
[ 1362.232164] [<80014504>] syscall_common+0x34/0x58

Here LEDS_TRIGGER_NETDEV is being enabled on an LED. It first takes
triggers_list_lock and then RTNL. A classical AB-BA deadlock.

phy_led_triggers_registers() does not require the RTNL, it does not
make any calls into the network stack which require protection. There
is also no requirement the PHY has been attached to a MAC, the
triggers only make use of phydev state. This allows the call to
phy_led_triggers_registers() to be placed elsewhere. PHY probe() and
release() don't hold RTNL, so solving the AB-BA deadlock.

En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad:

net: phy: registrar los led_triggers del phy durante la sonda para evitar un interbloqueo AB-BA

Existe un interbloqueo AB-BA cuando tanto LEDS_TRIGGER_NETDEV como LED_TRIGGER_PHY están habilitados:

[ 1362.049207] [&lt;8054e4b8&gt;] led_trigger_register+0x5c/0x1fc &lt;-- Intentando obtener el bloqueo 'triggers_list_lock' a través de down_write(&amp;triggers_list_lock);
[ 1362.054536] [&lt;80662830&gt;] phy_led_triggers_register+0xd0/0x234
[ 1362.060329] [&lt;8065e200&gt;] phy_attach_direct+0x33c/0x40c
[ 1362.065489] [&lt;80651fc4&gt;] phylink_fwnode_phy_connect+0x15c/0x23c
[ 1362.071480] [&lt;8066ee18&gt;] mtk_open+0x7c/0xba0
[ 1362.075849] [&lt;806d714c&gt;] __dev_open+0x280/0x2b0
[ 1362.080384] [&lt;806d7668&gt;] __dev_change_flags+0x244/0x24c
[ 1362.085598] [&lt;806d7698&gt;] dev_change_flags+0x28/0x78
[ 1362.090528] [&lt;807150e4&gt;] dev_ioctl+0x4c0/0x654 &lt;-- Mantiene el bloqueo 'rtnl_mutex' al llamar a rtnl_lock();
[ 1362.094985] [&lt;80694360&gt;] sock_ioctl+0x2f4/0x4e0
[ 1362.099567] [&lt;802e9c4c&gt;] sys_ioctl+0x32c/0xd8c
[ 1362.104022] [&lt;80014504&gt;] syscall_common+0x34/0x58

Aquí LED_TRIGGER_PHY está registrando los disparadores LED durante phy_attach mientras mantiene RTNL y luego toma triggers_list_lock.

[ 1362.191101] [&lt;806c2640&gt;] register_netdevice_notifier+0x60/0x168 &lt;-- Intentando obtener el bloqueo 'rtnl_mutex' a través de rtnl_lock();
[ 1362.197073] [&lt;805504ac&gt;] netdev_trig_activate+0x194/0x1e4
[ 1362.202490] [&lt;8054e28c&gt;] led_trigger_set+0x1d4/0x360 &lt;-- Mantiene el bloqueo 'triggers_list_lock' mediante down_read(&amp;triggers_list_lock);
[ 1362.207511] [&lt;8054eb38&gt;] led_trigger_write+0xd8/0x14c
[ 1362.212566] [&lt;80381d98&gt;] sysfs_kf_bin_write+0x80/0xbc
[ 1362.217688] [&lt;8037fcd8&gt;] kernfs_fop_write_iter+0x17c/0x28c
[ 1362.223174] [&lt;802cbd70&gt;] vfs_write+0x21c/0x3c4
[ 1362.227712] [&lt;802cc0c4&gt;] ksys_write+0x78/0x12c
[ 1362.232164] [&lt;80014504&gt;] syscall_common+0x34/0x58

Aquí LEDS_TRIGGER_NETDEV está siendo habilitado en un LED. Primero toma triggers_list_lock y luego RTNL. Un interbloqueo AB-BA clásico.

phy_led_triggers_registers() no requiere el RTNL, no realiza ninguna llamada a la pila de red que requiera protección. Tampoco existe el requisito de que el PHY haya sido conectado a un MAC, los disparadores solo hacen uso del estado de phydev. Esto permite que la llamada a phy_led_triggers_registers() se coloque en otro lugar. PHY probe() y release() no mantienen RTNL, resolviendo así el interbloqueo AB-BA.