# CVE-2025-40064: smc: Fix use-after-free in __pnet_find_base_ndev().

> A use-after-free vulnerability in the Linux kernel's SMC protocol allows attackers to trigger memory corruption, potentially leading to code execution or system crashes.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 Oct 2025
- **Updated:** 2 Sep 2026
- **Also known as:** AZL-68897, BELL-CVE-2025-40064, DEBIAN-CVE-2025-40064, GHSA-c442-5cxr-p4xq, ROOT-OS-DEBIAN-11-CVE-2025-40064, ROOT-OS-DEBIAN-12-CVE-2025-40064, ROOT-OS-DEBIAN-13-CVE-2025-40064, ROOT-OS-UBUNTU-2204-CVE-2025-40064, ROOT-OS-UBUNTU-2404-CVE-2025-40064, UBUNTU-CVE-2025-40064

## What is CVE-2025-40064?

CVE-2025-40064 is a high-severity use after free vulnerability in Linux, published on 28 Oct 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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---

## Which versions are affected by CVE-2025-40064?


## How do I fix CVE-2025-40064?

Apply the vendor's patch.

## Is CVE-2025-40064 being exploited?

There is no known exploitation of CVE-2025-40064 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40064 and fix it if it is affected.

What it is: CVE-2025-40064 is a high-severity use after free vulnerability in Linux, published on 28 Oct 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-40064 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-40064/ (Markdown: https://insights.sbomify.com/CVE-2025-40064/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40064
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40064
- OSV: https://osv.dev/vulnerability/CVE-2025-40064

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40064/
Summaries are generated and may contain mistakes; the official description above is the record.