{"id":"DEBIAN-CVE-2026-63809","details":"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:    \u003cTASK\u003e    ? __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    ...    \u003c/TASK\u003e  With this fix applied on top of the same test setup, rerunning the reproducer with fail-nth=1 yields no corresponding Oops reports.","modified":"2026-09-14T17:03:44.625942144Z","published":"2026-07-19T12:16:53.757Z","upstream":["CVE-2026-63809"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2026-63809"}],"affected":[{"package":{"name":"linux","ecosystem":"Debian:12","purl":"pkg:deb/debian/linux?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.1.177-1"}]}],"versions":["6.1.106-1","6.1.106-2","6.1.106-3","6.1.112-1","6.1.115-1","6.1.119-1","6.1.123-1","6.1.124-1","6.1.128-1","6.1.129-1","6.1.133-1","6.1.135-1","6.1.137-1","6.1.139-1","6.1.140-1","6.1.147-1","6.1.148-1","6.1.153-1","6.1.158-1","6.1.159-1","6.1.162-1","6.1.164-1","6.1.170-1","6.1.170-2","6.1.170-3","6.1.172-1","6.1.174-1","6.1.176-1","6.1.27-1","6.1.37-1","6.1.38-1","6.1.38-2","6.1.38-2~bpo11+1","6.1.38-3","6.1.38-4","6.1.38-4~bpo11+1","6.1.52-1","6.1.55-1","6.1.55-1~bpo11+1","6.1.64-1","6.1.66-1","6.1.67-1","6.1.69-1","6.1.69-1~bpo11+1","6.1.76-1","6.1.76-1~bpo11+1","6.1.82-1","6.1.85-1","6.1.90-1","6.1.90-1~bpo11+1","6.1.94-1","6.1.94-1~bpo11+1","6.1.98-1","6.1.99-1"],"ecosystem_specific":{"urgency":"not 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