title: dpll: fix possible deadlock during netlink dump operation
description: 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.
affected:
{
product: Linux
vendor: Linux
defaultStatus: unaffected
repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
versions:
version: 9d71b54b65b1, lessThan: 087739cbd0d0, status: affected, versionType: git
version: 9d71b54b65b1, lessThan: 53c0441dd2c4, status: affected, versionType: git
}
{
product: Linux
vendor: Linux
defaultStatus: affected
repo: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
versions:
version: 6.7, status: affected
version: 0, lessThan: 6.7, status: unaffected, versionType: custom
version: 6.7.6, lessThanOrEqual: 6.7.*, status: unaffected, versionType: custom
version: 6.8, lessThanOrEqual: *, status: unaffected, versionType: original_commit_for_fix
}
