CVE-2026-63809

bpf: use kvfree() for replaced sysctl write buffer

State: Published
Severity: 7.8 High
Published: Jul 19, 2026
Updated: Oct 19, 2026
Reserved: Jul 19, 2026

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.

Scores

CVSS	Score	Vector	Source
3.1	7.8 High	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H	Linux

Weaknesses

CWE-787 Out-of-bounds Write

Affected Products

Product	Versions
LinuxLinux	b7925acd82926ebbf94a0f0783a3961f4e558856 to before d0a81ed5ff5d0f9c3f63a4f9e5a4642c363ecd3eAffected 4508943794efdd94171549c0bd52810e2f4ad9fe to before 77355ef7a9f6b0d2bdf65be3b37f2c1f365e20d2Affected 4508943794efdd94171549c0bd52810e2f4ad9fe to before e1d1e203a6000804c5d3b8a4aa4e52303c0c7ab2Affected 4508943794efdd94171549c0bd52810e2f4ad9fe to before 81fc9a13acae99966232f0e055eb2e445263b89aAffected 4508943794efdd94171549c0bd52810e2f4ad9fe to before 838fe9c28121777c59a9406710a68fcf77bb8017Affected 4508943794efdd94171549c0bd52810e2f4ad9fe to before 65bd0c0afb0e1bf3287458e342429b069624f7d4Affected 4508943794efdd94171549c0bd52810e2f4ad9fe to before 70df4de46577fab5e25418f014583155a147c902Affected 4508943794efdd94171549c0bd52810e2f4ad9fe to before 4c21b5927d4364bfe7365f2700da5fea0ed0d004Affected 66258ab303588936ee1ee0794d9a271be24f73cbAffected 5.10.20 to before 5.10.260Affected 5.11.3 to before 5.12Affected
LinuxLinux	5.12Affected before 5.12Not affected 5.10.260 through 5.10.Not affected 5.15.211 through 5.15.Not affected 6.1.177 through 6.1.Not affected 6.6.144 through 6.6.Not affected 6.12.95 through 6.12.Not affected 6.18.38 through 6.18.Not affected 7.1.3 through 7.1.*Not affected 7.2 and laterNot affected

Product

Versions

LinuxLinux

b7925acd82926ebbf94a0f0783a3961f4e558856 to before d0a81ed5ff5d0f9c3f63a4f9e5a4642c363ecd3eAffected
4508943794efdd94171549c0bd52810e2f4ad9fe to before 77355ef7a9f6b0d2bdf65be3b37f2c1f365e20d2Affected
4508943794efdd94171549c0bd52810e2f4ad9fe to before e1d1e203a6000804c5d3b8a4aa4e52303c0c7ab2Affected
4508943794efdd94171549c0bd52810e2f4ad9fe to before 81fc9a13acae99966232f0e055eb2e445263b89aAffected
4508943794efdd94171549c0bd52810e2f4ad9fe to before 838fe9c28121777c59a9406710a68fcf77bb8017Affected
4508943794efdd94171549c0bd52810e2f4ad9fe to before 65bd0c0afb0e1bf3287458e342429b069624f7d4Affected
4508943794efdd94171549c0bd52810e2f4ad9fe to before 70df4de46577fab5e25418f014583155a147c902Affected
4508943794efdd94171549c0bd52810e2f4ad9fe to before 4c21b5927d4364bfe7365f2700da5fea0ed0d004Affected
66258ab303588936ee1ee0794d9a271be24f73cbAffected
5.10.20 to before 5.10.260Affected
5.11.3 to before 5.12Affected

LinuxLinux

5.12Affected
before 5.12Not affected
5.10.260 through 5.10.*Not affected
5.15.211 through 5.15.*Not affected
6.1.177 through 6.1.*Not affected
6.6.144 through 6.6.*Not affected
6.12.95 through 6.12.*Not affected
6.18.38 through 6.18.*Not affected
7.1.3 through 7.1.*Not affected
7.2 and laterNot affected

References

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