CVE-2025-40064 in Linux
Summary
by MITRE • 10/28/2025
In the Linux kernel, the following vulnerability has been resolved:
smc: Fix use-after-free in __pnet_find_base_ndev().
syzbot reported use-after-free of net_device in __pnet_find_base_ndev(), which was called during connect(). [0]
smc_pnet_find_ism_resource() fetches sk_dst_get(sk)->dev and passes down to pnet_find_base_ndev(), where RTNL is held. Then, UAF happened at __pnet_find_base_ndev() when the dev is first used.
This means dev had already been freed before acquiring RTNL in pnet_find_base_ndev().
While dev is going away, dst->dev could be swapped with blackhole_netdev, and the dev's refcnt by dst will be released.
We must hold dev's refcnt before calling smc_pnet_find_ism_resource().
Also, smc_pnet_find_roce_resource() has the same problem.
Let's use __sk_dst_get() and dst_dev_rcu() in the two functions.
[0]:
BUG: KASAN: use-after-free in __pnet_find_base_ndev+0x1b1/0x1c0 net/smc/smc_pnet.c:926 Read of size 1 at addr ffff888036bac33a by task syz.0.3632/18609
CPU: 1 UID: 0 PID: 18609 Comm: syz.0.3632 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025 Call Trace: <TASK> dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:378 [inline]
print_report+0xca/0x240 mm/kasan/report.c:482 kasan_report+0x118/0x150 mm/kasan/report.c:595 __pnet_find_base_ndev+0x1b1/0x1c0 net/smc/smc_pnet.c:926 pnet_find_base_ndev net/smc/smc_pnet.c:946 [inline]
smc_pnet_find_ism_by_pnetid net/smc/smc_pnet.c:1103 [inline]
smc_pnet_find_ism_resource+0xef/0x390 net/smc/smc_pnet.c:1154 smc_find_ism_device net/smc/af_smc.c:1030 [inline]
smc_find_proposal_devices net/smc/af_smc.c:1115 [inline]
__smc_connect+0x372/0x1890 net/smc/af_smc.c:1545 smc_connect+0x877/0xd90 net/smc/af_smc.c:1715 __sys_connect_file net/socket.c:2086 [inline]
__sys_connect+0x313/0x440 net/socket.c:2105 __do_sys_connect net/socket.c:2111 [inline]
__se_sys_connect net/socket.c:2108 [inline]
__x64_sys_connect+0x7a/0x90 net/socket.c:2108 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f47cbf8eba9 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f47ccdb1038 EFLAGS: 00000246 ORIG_RAX: 000000000000002a RAX: ffffffffffffffda RBX: 00007f47cc1d5fa0 RCX: 00007f47cbf8eba9 RDX: 0000000000000010 RSI: 0000200000000280 RDI: 000000000000000b RBP: 00007f47cc011e19 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f47cc1d6038 R14: 00007f47cc1d5fa0 R15: 00007ffc512f8aa8 </TASK>
The buggy address belongs to the physical page: page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888036bacd00 pfn:0x36bac flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff) raw: 00fff00000000000 ffffea0001243d08 ffff8880b863fdc0 0000000000000000 raw: ffff888036bacd00 0000000000000000 00000000ffffffff 0000000000000000 page dumped because: kasan: bad access detected page_owner tracks the page as freed page last allocated via order 2, migratetype Unmovable, gfp_mask 0x446dc0(GFP_KERNEL_ACCOUNT|__GFP_ZERO|__GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_COMP), pid 16741, tgid 16741 (syz-executor), ts 343313197788, free_ts 380670750466 set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1851 prep_new_page mm/page_alloc.c:1859 [inline]
get_page_from_freelist+0x21e4/0x22c0 mm/page_alloc.c:3858 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5148 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416 ___kmalloc_large_node+0x5f/0x1b0 mm/slub.c:4317 __kmalloc_large_node_noprof+0x18/0x90 mm/slub.c:4348 __do_kmalloc_node mm/slub.c:4364 [inline]
__kvmalloc_node ---truncated---
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Analysis
by VulDB Data Team • 05/20/2026
The vulnerability identified as CVE-2025-40064 resides within the Linux kernel's SMC (Scalable Meta Communication) subsystem, specifically in the handling of network device references during socket connection operations. This issue manifests as a use-after-free (UAF) condition in the function `__pnet_find_base_ndev()`, which is invoked during the `connect()` system call. The UAF arises due to improper management of reference counts for network device structures, leading to potential exploitation for privilege escalation or system instability. The root cause lies in the timing of when network device references are acquired and released, particularly in the context of the routing table lock (RTNL) and the lifecycle of network device objects.
The flaw occurs when `smc_pnet_find_ism_resource()` retrieves a destination device via `sk_dst_get(sk)->dev` and passes it to `pnet_find_base_ndev()`, where RTNL is held. However, the device reference may have already been freed by the time the function attempts to access it, resulting in a memory access violation. This situation is exacerbated by the fact that the device's reference count may be released during the transition of `dst->dev` to a `blackhole_netdev` during device teardown, while the reference is still held by the destination cache. The vulnerability affects not only `smc_pnet_find_ism_resource()` but also `smc_pnet_find_roce_resource()`, indicating a broader class of issues within the SMC subsystem's resource handling logic.
The technical impact of this vulnerability extends beyond simple memory corruption, as it provides a potential attack vector for malicious actors to exploit kernel memory management flaws. The use-after-free condition can be leveraged to execute arbitrary code with kernel privileges, depending on the specific memory layout and exploitation techniques employed. The vulnerability is classified under CWE-416, which describes the use of freed memory, and aligns with ATT&CK techniques related to privilege escalation and kernel exploitation. This issue is particularly concerning in environments where SMC is actively used, as it could allow unprivileged users to gain elevated privileges or cause denial of service through controlled memory corruption.
Mitigation strategies for this vulnerability involve ensuring that network device references are properly protected before being passed to functions that may access them under lock contexts. The fix requires the implementation of proper reference counting mechanisms using `__sk_dst_get()` and `dst_dev_rcu()` in both `smc_pnet_find_ism_resource()` and `smc_pnet_find_roce_resource()`. These changes ensure that device reference counts are maintained throughout the critical sections of code, preventing premature release of device structures. Additionally, kernel administrators should apply the patched kernel version immediately to prevent exploitation, as the vulnerability is actively being monitored by security researchers and may be weaponized in the wild. System hardening measures including kernel address space layout randomization and strict memory access controls can further reduce the risk of successful exploitation, though the core fix remains essential for addressing the root cause of the use-after-free condition.