{"id":"DEBIAN-CVE-2021-47408","details":"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 \u003e/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-\u003ef_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---","modified":"2026-09-15T09:02:32.027975970Z","published":"2024-05-21T15:15:26.337Z","upstream":["CVE-2021-47408"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2021-47408"}],"affected":[{"package":{"name":"linux","ecosystem":"Debian:12","purl":"pkg:deb/debian/linux?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.14.12-1"}]}],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2021-47408.json"}},{"package":{"name":"linux","ecosystem":"Debian:13","purl":"pkg:deb/debian/linux?arch=source&distro=trixie"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.14.12-1"}]}],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2021-47408.json"}},{"package":{"name":"linux","ecosystem":"Debian:14","purl":"pkg:deb/debian/linux?arch=source&distro=forky"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.14.12-1"}]}],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2021-47408.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"}]}