CVE-2024-26725

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.