Linux Kernel AF_UNIX SOCKMAP Redirect Hides Inflight File Descriptors from the Garbage Collector, Leaking Inflight Sockets Indefinitely

Status: UPDATED  |  Advisory ID: CVE-2026-53005

Key Details

Affected Products, Subsystems & Sectors

What to Know

In the Linux kernel, the following vulnerability has been resolved:

af_unix: Drop all SCM attributes for SOCKMAP.

SOCKMAP can hide inflight fd from AF_UNIX GC.

When a socket in SOCKMAP receives skb with inflight fd,

sk_psock_verdict_data_ready() looks up the mapped socket and

enqueue skb to its psock->ingress_skb.

Since neither the old nor the new GC can inspect the psock

queue, the hidden skb leaks the inflight sockets. Note that

this cannot be detected via kmemleak because inflight sockets

are linked to a global list.

In addition, SOCKMAP redirect breaks the Tarjan-based GC's

assumption that unix_edge.successor is always alive, which

is no longer true once skb is redirected, resulting in

use-after-free below. [0]

Moreover, SOCKMAP does not call scm_stat_del() properly,

so unix_show_fdinfo() could report an incorrect fd count.

sk_msg_recvmsg() does not support any SCM attributes in the

first place.

Let's drop all SCM attributes before passing skb to the

SOCKMAP layer.

[0]:

BUG: KASAN: slab-use-after-free in unix_del_edges (net/unix/garbage.c:118 net/unix/garbage.c:181 net/unix/garbage.c:251)

Read of size 8 at addr ffff888125362670 by task kworker/56:1/496

CPU: 56 UID: 0 PID: 496 Comm: kworker/56:1 Not tainted 7.0.0-rc7-00263-gb9d8b856689d #3 PREEMPT(lazy)

Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-debian-1.17.0-1 04/01/2014

Workqueue: events sk_psock_backlog

Call Trace:

<TASK>

dump_stack_lvl (lib/dump_stack.c:122)

print_report (mm/kasan/report.c:379)

kasan_report (mm/kasan/report.c:597)

unix_del_edges (net/unix/garbage.c:118 net/unix/garbage.c:181 net/unix/garbage.c:251)

unix_destroy_fpl (net/unix/garbage.c:317)

unix_destruct_scm (./include/net/scm.h:80 ./include/net/scm.h:86 net/unix/af_unix.c:1976)

sk_psock_backlog (./include/linux/skbuff.h:?)

process_scheduled_works (kernel/workqueue.c:?)

worker_thread (kernel/workqueue.c:?)

kthread (kernel/kthread.c:438)

ret_from_fork (arch/x86/kernel/process.c:164)

ret_from_fork_asm (arch/x86/entry/entry_64.S:258)

</TASK>

Allocated by task 955:

kasan_save_track (mm/kasan/common.c:58 mm/kasan/common.c:78)

__kasan_slab_alloc (mm/kasan/common.c:369)

kmem_cache_alloc_noprof (mm/slub.c:4539)

sk_prot_alloc (net/core/sock.c:2240)

sk_alloc (net/core/sock.c:2301)

unix_create1 (net/unix/af_unix.c:1099)

unix_create (net/unix/af_unix.c:1169)

__sock_create (net/socket.c:1606)

__sys_socketpair (net/socket.c:1811)

__x64_sys_socketpair (net/socket.c:1863 net/socket.c:1860 net/socket.c:1860)

do_syscall_64 (arch/x86/entry/syscall_64.c:?)

entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)

Freed by task 496:

kasan_save_track (mm/kasan/common.c:58 mm/kasan/common.c:78)

kasan_save_free_info (mm/kasan/generic.c:587)

__kasan_slab_free (mm/kasan/common.c:287)

kmem_cache_free (mm/slub.c:6165)

__sk_destruct (net/core/sock.c:2282 net/core/sock.c:2384)

sk_psock_destroy (./include/net/sock.h:?)

process_scheduled_works (kernel/workqueue.c:?)

worker_thread (kernel/workqueue.c:?)

kthread (kernel/kthread.c:438)

ret_from_fork (arch/x86/kernel/process.c:164)

ret_from_fork_asm (arch/x86/entry/entry_64.S:258) (NVD)

What to Do

Monitor Linux's web page for any future patch releases.

References