Re: [PATCH net] net/smc: fix UAF on smcsk after smc_listen_out()

Dust Li
2025-08-18T10:53:53Z

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@linux.alibaba.com>
>Reviewed-by: Guangguan Wang <guangguan.wang@linux.alibaba.com>
>Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>

Reviewed-by: Dust Li <dust.li@linux.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
>