netdev - Re: [PATCH net] net/smc: fix UAF on smcsk after smc_listen

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Message-ID: <aKMGNyMUUwq7ufT7@linux.alibaba.com>
Date: Mon, 18 Aug 2025 18:53:43 +0800
From: Dust Li <dust.li@...ux.alibaba.com>
To: "D. Wythe" <alibuda@...ux.alibaba.com>, Mahanta.Jambigi@....com,
	Sidraya.Jayagond@....com, wenjia@...ux.ibm.com,
	wintera@...ux.ibm.com, tonylu@...ux.alibaba.com,
	guwen@...ux.alibaba.com
Cc: kuba@...nel.org, davem@...emloft.net, netdev@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org,
	pabeni@...hat.com, edumazet@...gle.com, jaka@...ux.ibm.com
Subject: Re: [PATCH net] net/smc: fix UAF on smcsk after smc_listen_out()

On 2025-08-18 13:46:18, D. Wythe wrote:
>BPF CI testing report a UAF issue:
>
>  [   16.446633] BUG: kernel NULL pointer dereference, address: 000000000000003  0
>  [   16.447134] #PF: supervisor read access in kernel mod  e
>  [   16.447516] #PF: error_code(0x0000) - not-present pag  e
>  [   16.447878] PGD 0 P4D   0
>  [   16.448063] Oops: Oops: 0000 [#1] PREEMPT SMP NOPT  I
>  [   16.448409] CPU: 0 UID: 0 PID: 9 Comm: kworker/0:1 Tainted: G           OE      6.13.0-rc3-g89e8a75fda73-dirty #4  2
>  [   16.449124] Tainted: [O]=OOT_MODULE, [E]=UNSIGNED_MODUL  E
>  [   16.449502] Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/201  4
>  [   16.450201] Workqueue: smc_hs_wq smc_listen_wor  k
>  [   16.450531] RIP: 0010:smc_listen_work+0xc02/0x159  0
>  [   16.452158] RSP: 0018:ffffb5ab40053d98 EFLAGS: 0001024  6
>  [   16.452526] RAX: 0000000000000001 RBX: 0000000000000002 RCX: 000000000000030  0
>  [   16.452994] RDX: 0000000000000280 RSI: 00003513840053f0 RDI: 000000000000000  0
>  [   16.453492] RBP: ffffa097808e3800 R08: ffffa09782dba1e0 R09: 000000000000000  5
>  [   16.453987] R10: 0000000000000000 R11: 0000000000000000 R12: ffffa0978274640  0
>  [   16.454497] R13: 0000000000000000 R14: 0000000000000000 R15: ffffa09782d4092  0
>  [   16.454996] FS:  0000000000000000(0000) GS:ffffa097bbc00000(0000) knlGS:000000000000000  0
>  [   16.455557] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003  3
>  [   16.455961] CR2: 0000000000000030 CR3: 0000000102788004 CR4: 0000000000770ef  0
>  [   16.456459] PKRU: 5555555  4
>  [   16.456654] Call Trace  :
>  [   16.456832]  <TASK  >
>  [   16.456989]  ? __die+0x23/0x7  0
>  [   16.457215]  ? page_fault_oops+0x180/0x4c  0
>  [   16.457508]  ? __lock_acquire+0x3e6/0x249  0
>  [   16.457801]  ? exc_page_fault+0x68/0x20  0
>  [   16.458080]  ? asm_exc_page_fault+0x26/0x3  0
>  [   16.458389]  ? smc_listen_work+0xc02/0x159  0
>  [   16.458689]  ? smc_listen_work+0xc02/0x159  0
>  [   16.458987]  ? lock_is_held_type+0x8f/0x10  0
>  [   16.459284]  process_one_work+0x1ea/0x6d  0
>  [   16.459570]  worker_thread+0x1c3/0x38  0
>  [   16.459839]  ? __pfx_worker_thread+0x10/0x1  0
>  [   16.460144]  kthread+0xe0/0x11  0
>  [   16.460372]  ? __pfx_kthread+0x10/0x1  0
>  [   16.460640]  ret_from_fork+0x31/0x5  0
>  [   16.460896]  ? __pfx_kthread+0x10/0x1  0
>  [   16.461166]  ret_from_fork_asm+0x1a/0x3  0
>  [   16.461453]  </TASK  >
>  [   16.461616] Modules linked in: bpf_testmod(OE) [last unloaded: bpf_testmod(OE)  ]
>  [   16.462134] CR2: 000000000000003  0
>  [   16.462380] ---[ end trace 0000000000000000 ]---
>  [   16.462710] RIP: 0010:smc_listen_work+0xc02/0x1590
>
>The direct cause of this issue is that after smc_listen_out_connected(),
>newclcsock->sk may be NULL since it will releases the smcsk. Therefore,
>if the application closes the socket immediately after accept,
>newclcsock->sk can be NULL. A possible execution order could be as
>follows:
>
>smc_listen_work                                 | userspace
>-----------------------------------------------------------------
>lock_sock(sk)                                   |
>smc_listen_out_connected()                      |
>| \- smc_listen_out                             |
>|    | \- release_sock                          |
>     | |- sk->sk_data_ready()                   |
>                                                | fd = accept();
>                                                | close(fd);
>                                                |  \- socket->sk = NULL;
>/* newclcsock->sk is NULL now */
>SMC_STAT_SERV_SUCC_INC(sock_net(newclcsock->sk))
>
>Since smc_listen_out_connected() will not fail, simply swapping the order
>of the code can easily fix this issue.
>
>Fixes: 3b2dec2603d5 ("net/smc: restructure client and server code in af_smc")
>Signed-off-by: D. Wythe <alibuda@...ux.alibaba.com>
>Reviewed-by: Guangguan Wang <guangguan.wang@...ux.alibaba.com>
>Reviewed-by: Alexandra Winter <wintera@...ux.ibm.com>

Reviewed-by: Dust Li <dust.li@...ux.alibaba.com>

Best regards,
Dust

>---
> net/smc/af_smc.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
>diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
>index 9311c38f7abe..e0e48f24cd61 100644
>--- a/net/smc/af_smc.c
>+++ b/net/smc/af_smc.c
>@@ -2568,8 +2568,9 @@ static void smc_listen_work(struct work_struct *work)
> 			goto out_decl;
> 	}
> 
>-	smc_listen_out_connected(new_smc);
> 	SMC_STAT_SERV_SUCC_INC(sock_net(newclcsock->sk), ini);
>+	/* smc_listen_out() will release smcsk */
>+	smc_listen_out_connected(new_smc);
> 	goto out_free;
> 
> out_unlock:
>-- 
>2.45.0
>