In the Linux kernel, the following vulnerability has been resolved: netlink: avoid infinite retry looping in netlink_unicast() netlink_att

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).