bpf: use kvfree() for replaced sysctl write buffer

Description

In the Linux kernel, the following vulnerability has been resolved: bpf: use kvfree() for replaced sysctl write buffer proc_sys_call_handler() allocates its temporary sysctl buffer with kvzalloc() and passes it to __cgroup_bpf_run_filter_sysctl(). Since kvzalloc() may fall back to vmalloc() for large allocations, freeing that buffer with kfree() is wrong and can corrupt memory. Use kvfree() to safely handle both kmalloc and kvzalloc()/vmalloc allocations. The bug was first flagged by an experimental analysis tool we are developing for kernel memory-management bugs while analyzing v6.13-rc1. The tool is still under development and is not yet publicly available. Manual inspection confirms that the bug is still present in v7.1-rc5. Reproduced the bug based on v7.1-rc4 in a QEMU x86_64 guest booted with KASAN and CONFIG_FAILSLAB enabled. To exercise the replacement path, the test tree also included the accompanying fix for the stale ret == 1 check in __cgroup_bpf_run_filter_sysctl(). The reproducer confines failslab injections to the proc_sys_call_handler() range, uses stacktrace-depth=32, and injects fail-nth=1 while writing 8191 bytes to /proc/sys/kernel/domainname from a task in the target cgroup. Under that setup, fail-nth=1 triggered the fault: BUG: unable to handle page fault for address: ffffeb0200024d48 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: Oops: 0000 SMP KASAN NOPTI CPU: 2 UID: 0 PID: 209 Comm: repro_proc_sys_ Not tainted 7.1.0-rc4-00686-g97625979a5d4 PREEMPT(lazy) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014 RIP: 0010:kfree+0x6e/0x510 ... Call Trace: <TASK> ? __cgroup_bpf_run_filter_sysctl+0x626/0xc30 __cgroup_bpf_run_filter_sysctl+0x74d/0xc30 ? __pfx___cgroup_bpf_run_filter_sysctl+0x10/0x10 ? srso_return_thunk+0x5/0x5f ? __kvmalloc_node_noprof+0x345/0x870 ? proc_sys_call_handler+0x250/0x480 ? srso_return_thunk+0x5/0x5f proc_sys_call_handler+0x3a2/0x480 ? __pfx_proc_sys_call_handler+0x10/0x10 ? srso_return_thunk+0x5/0x5f ? selinux_file_permission+0x39f/0x500 ? srso_return_thunk+0x5/0x5f ? lock_is_held_type+0x9e/0x120 vfs_write+0x98e/0x1000 ... </TASK> With this fix applied on top of the same test setup, rerunning the reproducer with fail-nth=1 yields no corresponding Oops reports.

Timeline

Scores

EPSS (exploitation in 30 days)

0.15% · top 95% of all CVEs (11 Nov 2026)

CISA SSVC

Exploitation: none · Automatable: no · Technical impact: total

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.8.

Affected products

• Linux · Linux

  • affected b7925acd82926ebbf94a0f0783a3961f4e558856 – < d0a81ed5ff5d0f9c3f63a4f9e5a4642c363ecd3e
  • affected 4508943794efdd94171549c0bd52810e2f4ad9fe – < 77355ef7a9f6b0d2bdf65be3b37f2c1f365e20d2
  • affected 4508943794efdd94171549c0bd52810e2f4ad9fe – < e1d1e203a6000804c5d3b8a4aa4e52303c0c7ab2
  • affected 4508943794efdd94171549c0bd52810e2f4ad9fe – < 81fc9a13acae99966232f0e055eb2e445263b89a
  • affected 4508943794efdd94171549c0bd52810e2f4ad9fe – < 838fe9c28121777c59a9406710a68fcf77bb8017
  • affected 4508943794efdd94171549c0bd52810e2f4ad9fe – < 65bd0c0afb0e1bf3287458e342429b069624f7d4
  • affected 4508943794efdd94171549c0bd52810e2f4ad9fe – < 70df4de46577fab5e25418f014583155a147c902
  • affected 4508943794efdd94171549c0bd52810e2f4ad9fe – < 4c21b5927d4364bfe7365f2700da5fea0ed0d004
  • affected 66258ab303588936ee1ee0794d9a271be24f73cb
  • affected 5.10.20 – < 5.10.260
  • affected 5.11.3 – < 5.12

• Linux · Linux

  • affected 5.12
  • unaffected < 5.12
  • unaffected 5.10.260 – ≤ 5.10.*
  • unaffected 5.15.211 – ≤ 5.15.*
  • unaffected 6.1.177 – ≤ 6.1.*
  • unaffected 6.6.144 – ≤ 6.6.*
  • unaffected 6.12.95 – ≤ 6.12.*
  • unaffected 6.18.38 – ≤ 6.18.*
  • unaffected 7.1.3 – ≤ 7.1.*
  • unaffected 7.2 – ≤ *

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• EUVD EUVD-2026-45475 (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-63809](https://cveledger.app/badge/CVE-2026-63809.svg)](https://cveledger.app/cve/CVE-2026-63809)

Record last updated 19 Oct 2026, 20:07 UTC.