CVE-2025-38734

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

net/smc: fix UAF on smcsk after smc_listen_out()

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.

A race in the SMC server path allowed smc_listen_work() to dereference newclcsock->sk after it was cleared by smc_listen_out(), causing a kernel NULL-pointer dereference and crash.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.