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

net: fix data-races around sk->sk_forward_alloc

Syzkaller reported this warning:
——————[ cut here ]——————
WARNING: CPU: 0 PID: 16 at net/ipv4/af_inet.c:156 inet_sock_destruct+0x1c5/0x1e0
Modules linked in:
CPU: 0 UID: 0 PID: 16 Comm: ksoftirqd/0 Not tainted 6.12.0-rc5 #26
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
RIP: 0010:inet_sock_destruct+0x1c5/0x1e0
Code: 24 12 4c 89 e2 5b 48 c7 c7 98 ec bb 82 41 5c e9 d1 18 17 ff 4c 89 e6 5b 48 c7 c7 d0 ec bb 82 41 5c e9 bf 18 17 ff 0f 0b eb 83 <0f> 0b eb 97 0f 0b eb 87 0f 0b e9 68 ff ff ff 66 66 2e 0f 1f 84 00
RSP: 0018:ffffc9000008bd90 EFLAGS: 00010206
RAX: 0000000000000300 RBX: ffff88810b172a90 RCX: 0000000000000007
RDX: 0000000000000002 RSI: 0000000000000300 RDI: ffff88810b172a00
RBP: ffff88810b172a00 R08: ffff888104273c00 R09: 0000000000100007
R10: 0000000000020000 R11: 0000000000000006 R12: ffff88810b172a00
R13: 0000000000000004 R14: 0000000000000000 R15: ffff888237c31f78
FS: 0000000000000000(0000) GS:ffff888237c00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffc63fecac8 CR3: 000000000342e000 CR4: 00000000000006f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
? __warn+0x88/0x130
? inet_sock_destruct+0x1c5/0x1e0
? report_bug+0x18e/0x1a0
? handle_bug+0x53/0x90
? exc_invalid_op+0x18/0x70
? asm_exc_invalid_op+0x1a/0x20
? inet_sock_destruct+0x1c5/0x1e0
__sk_destruct+0x2a/0x200
rcu_do_batch+0x1aa/0x530
? rcu_do_batch+0x13b/0x530
rcu_core+0x159/0x2f0
handle_softirqs+0xd3/0x2b0
? __pfx_smpboot_thread_fn+0x10/0x10
run_ksoftirqd+0x25/0x30
smpboot_thread_fn+0xdd/0x1d0
kthread+0xd3/0x100
? __pfx_kthread+0x10/0x10
ret_from_fork+0x34/0x50
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1a/0x30
</TASK>
—–[ end trace 0000000000000000 ]—-

Its possible that two threads call tcp_v6_do_rcv()/sk_forward_alloc_add()
concurrently when sk->sk_state == TCP_LISTEN with sk->sk_lock unlocked,
which triggers a data-race around sk->sk_forward_alloc:
tcp_v6_rcv

tcp_v6_do_rcv
    skb_clone_and_charge_r
        sk_rmem_schedule
            __sk_mem_schedule
                sk_forward_alloc_add()
        skb_set_owner_r
            sk_mem_charge
                sk_forward_alloc_add()
    __kfree_skb
        skb_release_all
            skb_release_head_state
                sock_rfree
                    sk_mem_uncharge
                        sk_forward_alloc_add()
                        sk_mem_reclaim
                            // set local var reclaimable
                            __sk_mem_reclaim
                                sk_forward_alloc_add()

In this syzkaller testcase, two threads call
tcp_v6_do_rcv() with skb->truesize=768, the sk_forward_alloc changes like
this:
(cpu 1) | (cpu 2) | sk_forward_alloc
… | … | 0
__sk_mem_schedule() | | +4096 = 4096

                 | __sk_mem_schedule() | +4096 = 8192

sk_mem_charge() | | -768 = 7424

                 | sk_mem_charge()     | -768  = 6656

… | … |
sk_mem_uncharge() | | +768 = 7424
reclaimable=7424 | |

                 | sk_mem_uncharge()   | +768  = 8192
                 | reclaimable=8192    |

__sk_mem_reclaim() | | -4096 = 4096

                 | __sk_mem_reclaim()  | -8192 = -4096 != 0

The skb_clone_and_charge_r() should not be called in tcp_v6_do_rcv() when
sk->sk_state is TCP_LISTEN, it happens later in tcp_v6_syn_recv_sock().
Fix the same issue in dccp_v6_do_rcv().