netlink: avoid infinite retry looping in netlink_unicast()

Overview

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

netlink: avoid infinite retry looping in netlink_unicast()

netlink_attachskb() checks for the socket's read memory allocation constraints. Firstly, it has:

rmem < READ_ONCE(sk->sk_rcvbuf)

to check if the just increased rmem value fits into the socket's receive buffer. If not, it proceeds and tries to wait for the memory under:

rmem + skb->truesize > READ_ONCE(sk->sk_rcvbuf)

The checks don't cover the case when skb->truesize + sk->sk_rmem_alloc is equal to sk->sk_rcvbuf. Thus the function neither successfully accepts these conditions, nor manages to reschedule the task - and is called in retry loop for indefinite time which is caught as:

rcu: INFO: rcu_sched self-detected stall on CPU rcu: 0-....: (25999 ticks this GP) idle=ef2/1/0x4000000000000000 softirq=262269/262269 fqs=6212 (t=26000 jiffies g=230833 q=259957) NMI backtrace for cpu 0 CPU: 0 PID: 22 Comm: kauditd Not tainted 5.10.240 #68 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-4.fc42 04/01/2014 Call Trace: <IRQ> dump_stack lib/dump_stack.c:120 nmi_cpu_backtrace.cold lib/nmi_backtrace.c:105 nmi_trigger_cpumask_backtrace lib/nmi_backtrace.c:62 rcu_dump_cpu_stacks kernel/rcu/tree_stall.h:335 rcu_sched_clock_irq.cold kernel/rcu/tree.c:2590 update_process_times kernel/time/timer.c:1953 tick_sched_handle kernel/time/tick-sched.c:227 tick_sched_timer kernel/time/tick-sched.c:1399 __hrtimer_run_queues kernel/time/hrtimer.c:1652 hrtimer_interrupt kernel/time/hrtimer.c:1717 __sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1113 asm_call_irq_on_stack arch/x86/entry/entry_64.S:808 </IRQ>

netlink_attachskb net/netlink/af_netlink.c:1234 netlink_unicast net/netlink/af_netlink.c:1349 kauditd_send_queue kernel/audit.c:776 kauditd_thread kernel/audit.c:897 kthread kernel/kthread.c:328 ret_from_fork arch/x86/entry/entry_64.S:304

Restore the original behavior of the check which commit in Fixes accidentally missed when restructuring the code.

Found by Linux Verification Center (linuxtesting.org).

Affected

• Linux >= 9da025150b7c14a8390fc06aea314c0a4011e82c < 47d49fd07f86d1f55ea1083287303d237e9e0922
• Linux >= c4ceaac5c5ba0b992ee1dc88e2a02421549e5c98 < 6bee383ff83352a693d03efdf27cdd80742f71b2
• Linux >= fd69af06101090eaa60b3d216ae715f9c0a58e5b < f324959ad47e62e3cadaffa65d3cff790fb48529
• Linux >= 76602d8e13864524382b0687dc32cd8f19164d5a < d42b71a34f6b8a2d5c53df81169b03b8d8b5cf4e
• Linux >= 55baecb9eb90238f60a8350660d6762046ebd3bd < 346c820ef5135cf062fa3473da955ef8c5fb6929
• Linux >= 4b8e18af7bea92f8b7fb92d40aeae729209db250 < 44ddd7b1ae0b7edb2c832eb16798c827a05e58f0
• Linux >= cd7ff61bfffd7000143c42bbffb85eeb792466d6 < 78fcd69d55c5f11d7694c547eca767a1cfd38ec4
• Linux >= ae8f160e7eb24240a2a79fc4c815c6a0d4ee16cc < e8edc7de688791a337c068693f22e8d8b869df71
• Linux >= ae8f160e7eb24240a2a79fc4c815c6a0d4ee16cc < 759dfc7d04bab1b0b86113f1164dc1fec192b859
• Linux >= 5.4.296 < 5.4.297
• Linux >= 5.10.240 < 5.10.241
• Linux >= 5.15.189 < 5.15.190
• Linux >= 6.1.146 < 6.1.149
• Linux >= 6.6.99 < 6.6.103
• Linux >= 6.12.39 < 6.12.43
• Linux >= 6.15.7 < 6.15.11
• Linux 6.16

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.