In the Linux kernel, the following vulnerability has been resolved:
bpf: use kvfree() for replaced sysctl write buffer
procsyscall_handler() allocates its temporary sysctl buffer with kvzalloc() and passes it to __cgroupbpfrunfiltersysctl(). 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 x8664 guest booted with KASAN and CONFIGFAILSLAB enabled. To exercise the replacement path, the test tree also included the accompanying fix for the stale ret == 1 check in _cgroupbpfrunfiltersysctl(). The reproducer confines failslab injections to the procsyscallhandler() 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: errorcode(0x0000) - not-present page PGD 0 P4D 0 Oops: Oops: 0000 SMP KASAN NOPTI CPU: 2 UID: 0 PID: 209 Comm: reproprocsys 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> ? __cgroupbpfrunfiltersysctl+0x626/0xc30 __cgroupbpfrunfiltersysctl+0x74d/0xc30 ? pfxcgroupbpfrunfiltersysctl+0x10/0x10 ? srsoreturn_thunk+0x5/0x5f ? __kvmallocnodenoprof+0x345/0x870 ? procsyscallhandler+0x250/0x480 ? srsoreturnthunk+0x5/0x5f procsyscallhandler+0x3a2/0x480 ? __pfxprocsyscallhandler+0x10/0x10 ? srsoreturnthunk+0x5/0x5f ? selinuxfilepermission+0x39f/0x500 ? srsoreturnthunk+0x5/0x5f ? lockisheldtype+0x9e/0x120 vfswrite+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.
{
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63809.json",
"cna_assigner": "Linux"
}