# CVE-2025-40012: net/smc: fix warning in smc_rx_splice() when calling get_page()

> A use-after-free vulnerability in the Linux kernel's SMC network module allows attackers to potentially execute code or escalate privileges via improper memory handling.

- **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:** 20 Oct 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-40012, DEBIAN-CVE-2025-40012, GHSA-c4v9-hjfq-qw76, ROOT-OS-DEBIAN-13-CVE-2025-40012, ROOT-OS-UBUNTU-2204-CVE-2025-40012, ROOT-OS-UBUNTU-2404-CVE-2025-40012, UBUNTU-CVE-2025-40012

## What is CVE-2025-40012?

CVE-2025-40012 is a high-severity use after free vulnerability in Linux, published on 20 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:

net/smc: fix warning in smc_rx_splice() when calling get_page()

smc_lo_register_dmb() allocates DMB buffers with kzalloc(), which are
later passed to get_page() in smc_rx_splice(). Since kmalloc memory is
not page-backed, this triggers WARN_ON_ONCE() in get_page() and prevents
holding a refcount on the buffer. This can lead to use-after-free if
the memory is released before splice_to_pipe() completes.

Use folio_alloc() instead, ensuring DMBs are page-backed and safe for
get_page().

WARNING: CPU: 18 PID: 12152 at ./include/linux/mm.h:1330 smc_rx_splice+0xaf8/0xe20 [smc]
CPU: 18 UID: 0 PID: 12152 Comm: smcapp Kdump: loaded Not tainted 6.17.0-rc3-11705-g9cf4672ecfee #10 NONE
Hardware name: IBM 3931 A01 704 (z/VM 7.4.0)
Krnl PSW : 0704e00180000000 000793161032696c (smc_rx_splice+0xafc/0xe20 [smc])
           R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3
Krnl GPRS: 0000000000000000 001cee80007d3001 00077400000000f8 0000000000000005
           0000000000000001 001cee80007d3006 0007740000001000 001c000000000000
           000000009b0c99e0 0000000000001000 001c0000000000f8 001c000000000000
           000003ffcc6f7c88 0007740003e98000 0007931600000005 000792969b2ff7b8
Krnl Code: 0007931610326960: af000000		mc	0,0
           0007931610326964: a7f4ff43		brc	15,00079316103267ea
          #0007931610326968: af000000		mc	0,0
          >000793161032696c: a7f4ff3f		brc	15,00079316103267ea
           0007931610326970: e320f1000004	lg	%r2,256(%r15)
           0007931610326976: c0e53fd1b5f5	brasl	%r14,000793168fd5d560
           000793161032697c: a7f4fbb5		brc	15,00079316103260e6
           0007931610326980: b904002b		lgr	%r2,%r11
Call Trace:
 smc_rx_splice+0xafc/0xe20 [smc]
 smc_rx_splice+0x756/0xe20 [smc])
 smc_rx_recvmsg+0xa74/0xe00 [smc]
 smc_splice_read+0x1ce/0x3b0 [smc]
 sock_splice_read+0xa2/0xf0
 do_splice_read+0x198/0x240
 splice_file_to_pipe+0x7e/0x110
 do_splice+0x59e/0xde0
 __do_splice+0x11a/0x2d0
 __s390x_sys_splice+0x140/0x1f0
 __do_syscall+0x122/0x280
 system_call+0x6e/0x90
Last Breaking-Event-Address:
smc_rx_splice+0x960/0xe20 [smc]
---[ end trace 0000000000000000 ]---

## Which versions are affected by CVE-2025-40012?


## How do I fix CVE-2025-40012?

Apply the vendor's patch.

## Is CVE-2025-40012 being exploited?

There is no known exploitation of CVE-2025-40012 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40012 and fix it if it is affected.

What it is: CVE-2025-40012 is a high-severity use after free vulnerability in Linux, published on 20 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-2025-40012 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-2025-40012/ (Markdown: https://insights.sbomify.com/CVE-2025-40012/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40012
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40012
- OSV: https://osv.dev/vulnerability/CVE-2025-40012

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40012/
Summaries are generated and may contain mistakes; the official description above is the record.