CVE-2024-26725

En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: dpll: soluciona un posible punto muerto durante la operación de volcado de netlink Recientemente, he estado recibiendo la siguiente advertencia de punto muerto durante el volcado de pin de dpll: [52804.637962] =========== =========================================== [52804.638536] ADVERTENCIA: posible circular dependencia de bloqueo detectada [52804.639111] 6.8.0-rc2jiri+ #1 No contaminado [52804.639529] -------------------------------- ---------------------- [52804.640104] python3/2984 está intentando adquirir el bloqueo: [52804.640581] ffff88810e642678 (nlk_cb_mutex-GENERIC){+.+.}- {3:3}, en: netlink_dump+0xb3/0x780 [52804.641417] pero la tarea ya mantiene el bloqueo: [52804.642010] ffffffff83bde4c8 (dpll_lock){+.+.}-{3:3}, en: dpll_lock_dumpit+0x13/0x20 [52804.642747] qué bloqueo ya depende del nuevo bloqueo. [52804.643551] la cadena de dependencia existente (en orden inverso) es: [52804.644259] -> #1 (dpll_lock){+.+.}-{3:3}: [52804.644836] lock_acquire+0x174/0x3e0 [52804.645271] __mutex_lock+ 0x119/0x1150 [52804.645723] dpll_lock_dumpit+0x13/0x20 [52804.646169] genl_start+0x266/0x320 [52804.646578] __netlink_dump_start+0x321/0x450 [52804.647056 ] genl_family_rcv_msg_dumpit+0x155/0x1e0 [52804.647575] genl_rcv_msg+0x1ed/0x3b0 [52804.648001] netlink_rcv_skb+0xdc/ 0x210 [52804.648440] genl_rcv+0x24/0x40 [52804.648831] netlink_unicast+0x2f1/0x490 [52804.649290] netlink_sendmsg+0x36d/0x660 [52804.649742] __sock_sendmsg +0x73/0xc0 [52804.650165] __sys_sendto+0x184/0x210 [52804.650597] __x64_sys_sendto+0x72/0x80 [ 52804.651045] do_syscall_64+0x6f/0x140 [52804.651474] Entry_SYSCALL_64_after_hwframe+0x46/0x4e [52804.652001] -> #0 (nlk_cb_mutex-GENERIC){+.+.}-{3:3}: [52804.6 52650] check_prev_add+0x1ae/0x1280 [52804.653107 ] __lock_acquire+0x1ed3/0x29a0 [52804.653559] lock_acquire+0x174/0x3e0 [52804.653984] __mutex_lock+0x119/0x1150 [52804.654423] netlink_dump+0xb3/0x780 [52804.654 845] __netlink_dump_start+0x389/0x450 [52804.655321] genl_family_rcv_msg_dumpit+0x155/0x1e0 [52804.655842] genl_rcv_msg +0x1ed/0x3b0 [52804.656272] netlink_rcv_skb+0xdc/0x210 [52804.656721] genl_rcv+0x24/0x40 [52804.657119] netlink_unicast+0x2f1/0x490 [52804.657570] netlink_sendm sg+0x36d/0x660 [52804.658022] __sock_sendmsg+0x73/0xc0 [52804.658450] __sys_sendto+0x184 /0x210 [52804.658877] __x64_sys_sendto+0x72/0x80 [52804.659322] do_syscall_64+0x6f/0x140 [52804.659752] Entry_SYSCALL_64_after_hwframe+0x46/0x4e [52804.66 0281] otra información que podría ayudarnos a depurar esto: [52804.661077] Posible escenario de bloqueo inseguro: [52804.661671] CPU0 CPU1 [52804.662129] ---- ---- [52804.662577] bloqueo(dpll_lock); [52804.662924] bloqueo (nlk_cb_mutex-GENERIC); [52804.663538] bloqueo(dpll_lock); [52804.664073] bloqueo (nlk_cb_mutex-GENERIC); [52804.664490] El problema es el siguiente: __netlink_dump_start() llama a control->start(cb) con nlk->cb_mutex retenido. En control->start(cb) se toma dpll_lock. Luego, nlk->cb_mutex se libera y se toma nuevamente en netlink_dump(), mientras dpll_lock aún se mantiene. Eso lleva a un punto muerto de ABBA cuando otra CPU corre con la misma operación. Solucione este problema moviendo dpll_lock a la devolución de llamada dumpit(), lo que garantiza el orden correcto de toma de bloqueo.

A vulnerability was found in the Linux kernel, where an ABBA deadlock condition may be created if multiple CPUs attempt a DPLL netlink dump operation simultaneously. This deadlock could lead to performance issues.

In the Linux kernel, the following vulnerability has been resolved: dpll: fix possible deadlock during netlink dump operation Recently, I've been hitting following deadlock warning during dpll pin dump: [52804.637962] ====================================================== [52804.638536] WARNING: possible circular locking dependency detected [52804.639111] 6.8.0-rc2jiri+ #1 Not tainted [52804.639529] ------------------------------------------------------ [52804.640104] python3/2984 is trying to acquire lock: [52804.640581] ffff88810e642678 (nlk_cb_mutex-GENERIC){+.+.}-{3:3}, at: netlink_dump+0xb3/0x780 [52804.641417] but task is already holding lock: [52804.642010] ffffffff83bde4c8 (dpll_lock){+.+.}-{3:3}, at: dpll_lock_dumpit+0x13/0x20 [52804.642747] which lock already depends on the new lock. [52804.643551] the existing dependency chain (in reverse order) is: [52804.644259] -> #1 (dpll_lock){+.+.}-{3:3}: [52804.644836] lock_acquire+0x174/0x3e0 [52804.645271] __mutex_lock+0x119/0x1150 [52804.645723] dpll_lock_dumpit+0x13/0x20 [52804.646169] genl_start+0x266/0x320 [52804.646578] __netlink_dump_start+0x321/0x450 [52804.647056] genl_family_rcv_msg_dumpit+0x155/0x1e0 [52804.647575] genl_rcv_msg+0x1ed/0x3b0 [52804.648001] netlink_rcv_skb+0xdc/0x210 [52804.648440] genl_rcv+0x24/0x40 [52804.648831] netlink_unicast+0x2f1/0x490 [52804.649290] netlink_sendmsg+0x36d/0x660 [52804.649742] __sock_sendmsg+0x73/0xc0 [52804.650165] __sys_sendto+0x184/0x210 [52804.650597] __x64_sys_sendto+0x72/0x80 [52804.651045] do_syscall_64+0x6f/0x140 [52804.651474] entry_SYSCALL_64_after_hwframe+0x46/0x4e [52804.652001] -> #0 (nlk_cb_mutex-GENERIC){+.+.}-{3:3}: [52804.652650] check_prev_add+0x1ae/0x1280 [52804.653107] __lock_acquire+0x1ed3/0x29a0 [52804.653559] lock_acquire+0x174/0x3e0 [52804.653984] __mutex_lock+0x119/0x1150 [52804.654423] netlink_dump+0xb3/0x780 [52804.654845] __netlink_dump_start+0x389/0x450 [52804.655321] genl_family_rcv_msg_dumpit+0x155/0x1e0 [52804.655842] genl_rcv_msg+0x1ed/0x3b0 [52804.656272] netlink_rcv_skb+0xdc/0x210 [52804.656721] genl_rcv+0x24/0x40 [52804.657119] netlink_unicast+0x2f1/0x490 [52804.657570] netlink_sendmsg+0x36d/0x660 [52804.658022] __sock_sendmsg+0x73/0xc0 [52804.658450] __sys_sendto+0x184/0x210 [52804.658877] __x64_sys_sendto+0x72/0x80 [52804.659322] do_syscall_64+0x6f/0x140 [52804.659752] entry_SYSCALL_64_after_hwframe+0x46/0x4e [52804.660281] other info that might help us debug this: [52804.661077] Possible unsafe locking scenario: [52804.661671] CPU0 CPU1 [52804.662129] ---- ---- [52804.662577] lock(dpll_lock); [52804.662924] lock(nlk_cb_mutex-GENERIC); [52804.663538] lock(dpll_lock); [52804.664073] lock(nlk_cb_mutex-GENERIC); [52804.664490] The issue as follows: __netlink_dump_start() calls control->start(cb) with nlk->cb_mutex held. In control->start(cb) the dpll_lock is taken. Then nlk->cb_mutex is released and taken again in netlink_dump(), while dpll_lock still being held. That leads to ABBA deadlock when another CPU races with the same operation. Fix this by moving dpll_lock taking into dumpit() callback which ensures correct lock taking order.