netdev - Re: [RFC PATCH net v2] net: fix data-races around sk->sk_forward

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Message-ID: <CANn89iJ8mOqtOkMvrn6c892XrA_m3uf5FabmDWzA_pk-tTMCzw@mail.gmail.com>
Date: Tue, 5 Nov 2024 10:52:34 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Wang Liang <wangliang74@...wei.com>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, horms@...nel.org, 
	dsahern@...nel.org, kuniyu@...zon.com, luoxuanqiang@...inos.cn, 
	kernelxing@...cent.com, kirjanov@...il.com, yuehaibing@...wei.com, 
	zhangchangzhong@...wei.com, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH net v2] net: fix data-races around sk->sk_forward_alloc

On Tue, Nov 5, 2024 at 8:46 AM Wang Liang <wangliang74@...wei.com> wrote:
>
> 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().
>
> Suggested-by: Eric Dumazet <edumazet@...gle.com>
> Fixes: e994b2f0fb92 ("tcp: do not lock listener to process SYN packets")
> Signed-off-by: Wang Liang <wangliang74@...wei.com>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>

Thanks.