GHSA-VCHV-WVP9-HCW9
Vulnerability from github – Published: 2026-07-19 12:30 – Updated: 2026-07-20 15:31In 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: ? __cgroup_bpf_run_filter_sysctl+0x626/0xc30 __cgroup_bpf_run_filter_sysctl+0x74d/0xc30 ? __pfxcgroupbpf_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 ...
With this fix applied on top of the same test setup, rerunning the reproducer with fail-nth=1 yields no corresponding Oops reports.
{
"affected": [],
"aliases": [
"CVE-2026-63809"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-07-19T12:16:53Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: use kvfree() for replaced sysctl write buffer\n\nproc_sys_call_handler() allocates its temporary sysctl buffer with\nkvzalloc() and passes it to __cgroup_bpf_run_filter_sysctl(). Since\nkvzalloc() may fall back to vmalloc() for large allocations, freeing\nthat buffer with kfree() is wrong and can corrupt memory.\n\nUse kvfree() to safely handle both kmalloc and kvzalloc()/vmalloc\nallocations.\n\nThe bug was first flagged by an experimental analysis tool we are\ndeveloping for kernel memory-management bugs while analyzing\nv6.13-rc1. The tool is still under development and is not yet publicly\navailable. Manual inspection confirms that the bug is still\npresent in v7.1-rc5.\n\nReproduced the bug based on v7.1-rc4 in a QEMU x86_64 guest booted with\nKASAN and CONFIG_FAILSLAB enabled. To exercise the replacement path, the\ntest tree also included the accompanying fix for the stale ret == 1\ncheck in __cgroup_bpf_run_filter_sysctl(). The reproducer confines\nfailslab injections to the proc_sys_call_handler() range, uses\nstacktrace-depth=32, and injects fail-nth=1 while writing 8191 bytes to\n/proc/sys/kernel/domainname from a task in the target cgroup. Under\nthat setup, fail-nth=1 triggered the fault:\n\n BUG: unable to handle page fault for address: ffffeb0200024d48\n #PF: supervisor read access in kernel mode\n #PF: error_code(0x0000) - not-present page\n PGD 0 P4D 0\n Oops: Oops: 0000 SMP KASAN NOPTI\n CPU: 2 UID: 0 PID: 209 Comm: repro_proc_sys_ Not tainted 7.1.0-rc4-00686-g97625979a5d4 PREEMPT(lazy)\n Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014\n RIP: 0010:kfree+0x6e/0x510\n ...\n Call Trace:\n \u003cTASK\u003e\n ? __cgroup_bpf_run_filter_sysctl+0x626/0xc30\n __cgroup_bpf_run_filter_sysctl+0x74d/0xc30\n ? __pfx___cgroup_bpf_run_filter_sysctl+0x10/0x10\n ? srso_return_thunk+0x5/0x5f\n ? __kvmalloc_node_noprof+0x345/0x870\n ? proc_sys_call_handler+0x250/0x480\n ? srso_return_thunk+0x5/0x5f\n proc_sys_call_handler+0x3a2/0x480\n ? __pfx_proc_sys_call_handler+0x10/0x10\n ? srso_return_thunk+0x5/0x5f\n ? selinux_file_permission+0x39f/0x500\n ? srso_return_thunk+0x5/0x5f\n ? lock_is_held_type+0x9e/0x120\n vfs_write+0x98e/0x1000\n ...\n \u003c/TASK\u003e\n\nWith this fix applied on top of the same test setup, rerunning the\nreproducer with fail-nth=1 yields no corresponding Oops reports.",
"id": "GHSA-vchv-wvp9-hcw9",
"modified": "2026-07-20T15:31:47Z",
"published": "2026-07-19T12:30:23Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63809"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4c21b5927d4364bfe7365f2700da5fea0ed0d004"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/65bd0c0afb0e1bf3287458e342429b069624f7d4"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/70df4de46577fab5e25418f014583155a147c902"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/77355ef7a9f6b0d2bdf65be3b37f2c1f365e20d2"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/81fc9a13acae99966232f0e055eb2e445263b89a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/838fe9c28121777c59a9406710a68fcf77bb8017"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d0a81ed5ff5d0f9c3f63a4f9e5a4642c363ecd3e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e1d1e203a6000804c5d3b8a4aa4e52303c0c7ab2"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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