CVE-2021-47408

En el kernel de Linux, se resolvió la siguiente vulnerabilidad: netfilter: conntrack: serializar cambios de tamaño y limpiezas de hash. Syzbot pudo activar la siguiente advertencia [1] Syzbot aún no encontró ninguna reproducción, pero pude desencadenar un problema similar al tener 2 scripts ejecutándose en paralelo, cambiando los tamaños de hash de conntrack y: para j en `seq 1 1000`; dejar de compartir -n /bin/true >/dev/null ; done Se necesitarían más de 5 minutos para limpiar las estructuras net_namespace. Esto se debe a que nf_ct_iterate_cleanup() tiene que reiniciarse cada vez que ocurre un cambio de tamaño. Al agregar un mutex, podemos serializar los cambios de tamaño y las limpiezas de hash y también hacer que get_next_corpse() sea más rápido omitiendo los depósitos vacíos. Incluso sin cambios de tamaño en la imagen, este parche acelera considerablemente el desmantelamiento del espacio de nombres de la red. [1] INFORMACIÓN: la tarea syz-executor.0:8312 no puede morir durante más de 144 segundos. tarea:syz-executor.0 estado:R ejecutando pila de tareas:25672 pid: 8312 ppid: 6573 banderas:0x00004006 Seguimiento de llamadas: context_switch kernel/sched/core.c:4955 [en línea] __schedule+0x940/0x26f0 kernel/sched/core .c:6236 preempt_schedule_common+0x45/0xc0 kernel/sched/core.c:6408 preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:35 __local_bh_enable_ip+0x109/0x120 kernel/softirq.c:390 local_bh_enable include/ Linux /bottom_half.h:32 [en línea] get_next_corpse net/netfilter/nf_conntrack_core.c:2252 [en línea] nf_ct_iterate_cleanup+0x15a/0x450 net/netfilter/nf_conntrack_core.c:2275 nf_conntrack_cleanup_net_list+0x14c/0x4f0 net/netfilter/ nf_conntrack_core.c:2469 ops_exit_list+0x10d/0x160 net/core/net_namespace.c:171 setup_net+0x639/0xa30 net/core/net_namespace.c:349 copy_net_ns+0x319/0x760 net/core/net_namespace.c:470 create_new_namespaces+0x3f6/0xb20 kernel/nsproxy .c:110 unshare_nsproxy_namespaces+0xc1/0x1f0 kernel/nsproxy.c:226 ksys_unshare+0x445/0x920 kernel/fork.c:3128 __do_sys_unshare kernel/fork.c:3202 [en línea] __se_sys_unshare kernel/fork.c:3200 [en línea] __x64_sys_unshare+0x2d/0x40 kernel/fork.c:3200 do_syscall_x64 arch/x86/entry/common.c:50 [en línea] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 Entry_SYSCALL_64_after_hwframe+0x44/0xae : 0033:0x7f63da68e739 RSP: 002b:00007f63d7c05188 EFLAGS: 00000246 ORIG_RAX: 0000000000000110 RAX: ffffffffffffffda RBX: 00007f63da792f80 RCX: 63da68e739 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000040000000 RBP: 00007f63da6e8cc4 R08: 0000000000000000 R09: 000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f63da792f80 R13: 00007fff50b75d3f R14: 00007f63d7c05300 R15: 0000000000022000 Mostrando todos los bloqueos retenidos en el sistema: 1 bloqueo retenido por khungtaskd/27: #0: ffffffff8b980020 (rcu_read_lock){....}-{1:2}, : debug_show_all_locks+0x53 /0x260 kernel/locking/lockdep.c:6446 2 bloqueos retenidos por kworker/u4:2/153: #0: ffff888010c69138 ((wq_completion)events_unbound){+.+.}-{0:0}, en: arch_atomic64_set arch /x86/include/asm/atomic64_64.h:34 [en línea] #0: ffff888010c69138 ((wq_completion)events_unbound){+.+.}-{0:0}, en: arch_atomic_long_set include/linux/atomic/atomic-long .h:41 [en línea] #0: ffff888010c69138 ((wq_completion)events_unbound){+.+.}-{0:0}, en: atomic_long_set include/linux/atomic/atomic-instrumented.h:1198 [en línea] # 0: ffff888010c69138 ((wq_completion)events_unbound){+.+.}-{0:0}, en: set_work_data kernel/workqueue.c:634 [en línea] #0: ffff888010c69138 ((wq_completion)events_unbound){+.+. }-{0:0}, en: set_work_pool_and_clear_pending kernel/workqueue.c:661 [en línea] #0: ffff888010c69138 ((wq_completion)events_unbound){+.+.}-{0:0}, en: Process_one_work+0x896/ 0x1690 kernel/workqueue.c:2268 #1: ffffc9000140fdb0 ((kfence_timer).work){+.+.}-{0:0}, en: Process_one_work+0x8ca/0x1690 kernel/workqueue.c:2272 1 bloqueo retenido por systemd-udevd/2970: 1 bloqueo retenido por in:imklog/6258: #0: ffff88807f970ff0 (&f->f_pos_lock){+.+.}-{3:3}, en: __fdget_pos+0xe9/0x100 ---truncado---

A vulnerability was found in the Linux kernel’s netfilter and conntrack module, occurring during the resizing and cleanup of hash tables used for connection tracking. The kernel's nf_ct_iterate_cleanup() function fails to efficiently handle simultaneous hash resizes and cleanups, leading to prolonged delays lead to unresponsive system behavior.

In the Linux kernel, the following vulnerability has been resolved: netfilter: conntrack: serialize hash resizes and cleanups Syzbot was able to trigger the following warning [1] No repro found by syzbot yet but I was able to trigger similar issue by having 2 scripts running in parallel, changing conntrack hash sizes, and: for j in `seq 1 1000` ; do unshare -n /bin/true >/dev/null ; done It would take more than 5 minutes for net_namespace structures to be cleaned up. This is because nf_ct_iterate_cleanup() has to restart everytime a resize happened. By adding a mutex, we can serialize hash resizes and cleanups and also make get_next_corpse() faster by skipping over empty buckets. Even without resizes in the picture, this patch considerably speeds up network namespace dismantles. [1] INFO: task syz-executor.0:8312 can't die for more than 144 seconds. task:syz-executor.0 state:R running task stack:25672 pid: 8312 ppid: 6573 flags:0x00004006 Call Trace: context_switch kernel/sched/core.c:4955 [inline] __schedule+0x940/0x26f0 kernel/sched/core.c:6236 preempt_schedule_common+0x45/0xc0 kernel/sched/core.c:6408 preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:35 __local_bh_enable_ip+0x109/0x120 kernel/softirq.c:390 local_bh_enable include/linux/bottom_half.h:32 [inline] get_next_corpse net/netfilter/nf_conntrack_core.c:2252 [inline] nf_ct_iterate_cleanup+0x15a/0x450 net/netfilter/nf_conntrack_core.c:2275 nf_conntrack_cleanup_net_list+0x14c/0x4f0 net/netfilter/nf_conntrack_core.c:2469 ops_exit_list+0x10d/0x160 net/core/net_namespace.c:171 setup_net+0x639/0xa30 net/core/net_namespace.c:349 copy_net_ns+0x319/0x760 net/core/net_namespace.c:470 create_new_namespaces+0x3f6/0xb20 kernel/nsproxy.c:110 unshare_nsproxy_namespaces+0xc1/0x1f0 kernel/nsproxy.c:226 ksys_unshare+0x445/0x920 kernel/fork.c:3128 __do_sys_unshare kernel/fork.c:3202 [inline] __se_sys_unshare kernel/fork.c:3200 [inline] __x64_sys_unshare+0x2d/0x40 kernel/fork.c:3200 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x7f63da68e739 RSP: 002b:00007f63d7c05188 EFLAGS: 00000246 ORIG_RAX: 0000000000000110 RAX: ffffffffffffffda RBX: 00007f63da792f80 RCX: 00007f63da68e739 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000040000000 RBP: 00007f63da6e8cc4 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f63da792f80 R13: 00007fff50b75d3f R14: 00007f63d7c05300 R15: 0000000000022000 Showing all locks held in the system: 1 lock held by khungtaskd/27: #0: ffffffff8b980020 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x260 kernel/locking/lockdep.c:6446 2 locks held by kworker/u4:2/153: #0: ffff888010c69138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline] #0: ffff888010c69138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: arch_atomic_long_set include/linux/atomic/atomic-long.h:41 [inline] #0: ffff888010c69138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: atomic_long_set include/linux/atomic/atomic-instrumented.h:1198 [inline] #0: ffff888010c69138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: set_work_data kernel/workqueue.c:634 [inline] #0: ffff888010c69138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: set_work_pool_and_clear_pending kernel/workqueue.c:661 [inline] #0: ffff888010c69138 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work+0x896/0x1690 kernel/workqueue.c:2268 #1: ffffc9000140fdb0 ((kfence_timer).work){+.+.}-{0:0}, at: process_one_work+0x8ca/0x1690 kernel/workqueue.c:2272 1 lock held by systemd-udevd/2970: 1 lock held by in:imklog/6258: #0: ffff88807f970ff0 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:990 3 locks held by kworker/1:6/8158: 1 lock held by syz-executor.0/8312: 2 locks held by kworker/u4:13/9320: 1 lock held by ---truncated---