[PATCH] bpf, sockmap: fix deadlock in rcu_report_exp_cpu_mult

[Edward Adam Davis]

[Syzbot reported]
WARNING: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected
6.8.0-syzkaller-05221-gea80e3ed09ab #0 Not tainted
-----------------------------------------------------
rcu_exp_gp_kthr/18 [HC0[0]:SC0[2]:HE0:SE0] is trying to acquire:
ffff88802b5ab020 (&htab->buckets[i].lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffff88802b5ab020 (&htab->buckets[i].lock){+...}-{2:2}, at: sock_hash_delete_elem+0xb0/0x300 net/core/sock_map.c:939

and this task is already holding:
ffffffff8e136558 (rcu_node_0){-.-.}-{2:2}, at: sync_rcu_exp_done_unlocked+0xe/0x140 kernel/rcu/tree_exp.h:169
which would create a new lock dependency:
 (rcu_node_0){-.-.}-{2:2} -> (&htab->buckets[i].lock){+...}-{2:2}

but this new dependency connects a HARDIRQ-irq-safe lock:
 (rcu_node_0){-.-.}-{2:2}

.. which became HARDIRQ-irq-safe at:
  lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
  _raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162
  rcu_report_exp_cpu_mult+0x27/0x2f0 kernel/rcu/tree_exp.h:238
  csd_do_func kernel/smp.c:133 [inline]
  __flush_smp_call_function_queue+0xb2e/0x15b0 kernel/smp.c:542
  __sysvec_call_function_single+0xa8/0x3e0 arch/x86/kernel/smp.c:271
  instr_sysvec_call_function_single arch/x86/kernel/smp.c:266 [inline]
  sysvec_call_function_single+0x9e/0xc0 arch/x86/kernel/smp.c:266
  asm_sysvec_call_function_single+0x1a/0x20 arch/x86/include/asm/idtentry.h:709
  __sanitizer_cov_trace_switch+0x90/0x120
  update_event_printk kernel/trace/trace_events.c:2750 [inline]
  trace_event_eval_update+0x311/0xf90 kernel/trace/trace_events.c:2922
  process_one_work kernel/workqueue.c:3254 [inline]
  process_scheduled_works+0xa00/0x1770 kernel/workqueue.c:3335
  worker_thread+0x86d/0xd70 kernel/workqueue.c:3416
  kthread+0x2f0/0x390 kernel/kthread.c:388
  ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243

to a HARDIRQ-irq-unsafe lock:
 (&htab->buckets[i].lock){+...}-{2:2}

.. which became HARDIRQ-irq-unsafe at:
..
  lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
  __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
  _raw_spin_lock_bh+0x35/0x50 kernel/locking/spinlock.c:178
  spin_lock_bh include/linux/spinlock.h:356 [inline]
  sock_hash_delete_elem+0xb0/0x300 net/core/sock_map.c:939
  0xffffffffa0001b0e
  bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]
  __bpf_prog_run include/linux/filter.h:657 [inline]
  bpf_prog_run include/linux/filter.h:664 [inline]
  __bpf_trace_run kernel/trace/bpf_trace.c:2381 [inline]
  bpf_trace_run2+0x204/0x420 kernel/trace/bpf_trace.c:2420
  trace_contention_end+0xd7/0x100 include/trace/events/lock.h:122
  __mutex_lock_common kernel/locking/mutex.c:617 [inline]
  __mutex_lock+0x2e5/0xd70 kernel/locking/mutex.c:752
  futex_cleanup_begin kernel/futex/core.c:1091 [inline]
  futex_exit_release+0x34/0x1f0 kernel/futex/core.c:1143
  exit_mm_release+0x1a/0x30 kernel/fork.c:1652
  exit_mm+0xb0/0x310 kernel/exit.c:542
  do_exit+0x99e/0x27e0 kernel/exit.c:865
  do_group_exit+0x207/0x2c0 kernel/exit.c:1027
  __do_sys_exit_group kernel/exit.c:1038 [inline]
  __se_sys_exit_group kernel/exit.c:1036 [inline]
  __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1036
  do_syscall_64+0xfb/0x240
  entry_SYSCALL_64_after_hwframe+0x6d/0x75

other info that might help us debug this:

 Possible interrupt unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&htab->buckets[i].lock);
                               local_irq_disable();
                               lock(rcu_node_0);
                               lock(&htab->buckets[i].lock);
  <Interrupt>
    lock(rcu_node_0);

 *** DEADLOCK ***
[Fix]
Ensure that the context interrupt state is the same before and after using the
bucket->lock.

Reported-and-tested-by: syzbot+c4f4d25859c2e5859988@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
---
 net/core/sock_map.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 27d733c0f65e..ae8f81b26e16 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -932,11 +932,12 @@ static long sock_hash_delete_elem(struct bpf_map *map, void *key)
 	struct bpf_shtab_bucket *bucket;
 	struct bpf_shtab_elem *elem;
 	int ret = -ENOENT;
+	unsigned long flags;
 
 	hash = sock_hash_bucket_hash(key, key_size);
 	bucket = sock_hash_select_bucket(htab, hash);
 
-	spin_lock_bh(&bucket->lock);
+	spin_lock_irqsave(&bucket->lock, flags);
 	elem = sock_hash_lookup_elem_raw(&bucket->head, hash, key, key_size);
 	if (elem) {
 		hlist_del_rcu(&elem->node);
@@ -944,7 +945,7 @@ static long sock_hash_delete_elem(struct bpf_map *map, void *key)
 		sock_hash_free_elem(htab, elem);
 		ret = 0;
 	}
-	spin_unlock_bh(&bucket->lock);
+	spin_unlock_irqrestore(&bucket->lock, flags);
 	return ret;
 }
 
@@ -1136,6 +1137,7 @@ static void sock_hash_free(struct bpf_map *map)
 	struct bpf_shtab_elem *elem;
 	struct hlist_node *node;
 	int i;
+	unsigned long flags;
 
 	/* After the sync no updates or deletes will be in-flight so it
 	 * is safe to walk map and remove entries without risking a race
@@ -1151,11 +1153,11 @@ static void sock_hash_free(struct bpf_map *map)
 		 * exists, psock exists and holds a ref to socket. That
 		 * lets us to grab a socket ref too.
 		 */
-		spin_lock_bh(&bucket->lock);
+		spin_lock_irqsave(&bucket->lock, flags);
 		hlist_for_each_entry(elem, &bucket->head, node)
 			sock_hold(elem->sk);
 		hlist_move_list(&bucket->head, &unlink_list);
-		spin_unlock_bh(&bucket->lock);
+		spin_unlock_irqrestore(&bucket->lock, flags);
 
 		/* Process removed entries out of atomic context to
 		 * block for socket lock before deleting the psock's
-- 
2.43.0