recent_proc_net_exit() removes the /proc/net/xt_recent/ entries of a dying network namespace while holding spin_lock_bh(&recent_lock). remove_proc_entry() may sleep: proc_entry_rundown() waits until every task that is still inside the entry's file operations has left. A reader of such an entry is counted in by proc_reg_read() before recent_seq_start() takes recent_lock. So if a read is in flight when the namespace is torn down, cleanup_net() sleeps in atomic context holding the spinlock that the reader is spinning on, and neither side can ever make progress. An unprivileged user can trigger this from a user namespace by adding a rule with the "recent" match and reading its proc file while the namespace is being destroyed. As recent_lock is global, every later attempt to take it spins forever too: the spinning can spread to all CPUs, and network namespace teardown stops system-wide. BUG: sleeping function called from invalid context at kernel/sched/completion.c:116 #3: (recent_lock){+...}-{3:3}, at: recent_net_exit+0x2b/0x140 Workqueue: netns cleanup_net Call Trace: proc_entry_rundown+0x185/0x1b0 remove_proc_entry+0x21a/0x520 recent_net_exit+0x7f/0x140 cleanup_net+0x414/0x8f0 ... rcu: INFO: rcu_preempt self-detected stall on CPU Call Trace: queued_spin_lock_slowpath+0x313/0xc20 recent_seq_start+0x87/0x1b0 seq_read_iter+0x265/0x11e0 proc_reg_read+0x1ab/0x270 Fix by taking recent_mutex instead of recent_lock. According to commit a0e889bb1bdc ("[NETFILTER]: recent match: fix "sleeping function called from invalid context""), recent_mutex is the lock to use here: it protects recent_net->tables and was introduced so that proc entries are created and removed without recent_lock held, because those calls may sleep. hashlimit_proc_net_exit() does the same for xt_hashlimit. Fixes: 665e205c16c1 ("netfilter: xt_recent: fix namespace destroy path") Cc: stable@vger.kernel.org Cc: AutonomousCodeSecurity@microsoft.com Signed-off-by: Cen Zhang (Microsoft) --- net/netfilter/xt_recent.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/net/netfilter/xt_recent.c b/net/netfilter/xt_recent.c index 55f1f2d89952..00cccf003cff 100644 --- a/net/netfilter/xt_recent.c +++ b/net/netfilter/xt_recent.c @@ -650,14 +650,15 @@ static void __net_exit recent_proc_net_exit(struct net *net) /* recent_net_exit() is called before recent_mt_destroy(). Make sure * that the parent xt_recent proc entry is empty before trying to - * remove it. + * remove it. Use recent_mutex instead of recent_lock since + * remove_proc_entry() may sleep. */ - spin_lock_bh(&recent_lock); + mutex_lock(&recent_mutex); list_for_each_entry(t, &recent_net->tables, list) remove_proc_entry(t->name, recent_net->xt_recent); recent_net->xt_recent = NULL; - spin_unlock_bh(&recent_lock); + mutex_unlock(&recent_mutex); remove_proc_entry("xt_recent", net->proc_net); } -- 2.55.0