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* [PATCH bpf-next] xdp: Fix race in dev_map_hash_update_elem() when replacing element
       [not found] <0000000000005091a70591d3e1d9@google.com>
@ 2019-09-08  8:20 ` Toke Høiland-Jørgensen
  2019-09-08  8:33   ` Toke Høiland-Jørgensen
  0 siblings, 1 reply; 2+ messages in thread
From: Toke Høiland-Jørgensen @ 2019-09-08  8:20 UTC (permalink / raw)
  To: make-wifi-fast, linux-wireless, ast, bpf, daniel, davem, hawk,
	jakub.kicinski, john.fastabend, kafai, linux-kernel, netdev,
	songliubraving, syzkaller-bugs, yhs
  Cc: Toke Høiland-Jørgensen, syzbot+4e7a85b1432052e8d6f8

syzbot found a crash in dev_map_hash_update_elem(), when replacing an
element with a new one. Jesper correctly identified the cause of the crash
as a race condition between the initial lookup in the map (which is done
before taking the lock), and the removal of the old element.

Rather than just add a second lookup into the hashmap after taking the
lock, fix this by reworking the function logic to take the lock before the
initial lookup.

Fixes: 6f9d451ab1a3 ("xdp: Add devmap_hash map type for looking up devices by hashed index")
Reported-and-tested-by: syzbot+4e7a85b1432052e8d6f8@syzkaller.appspotmail.com
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 kernel/bpf/devmap.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index 9af048a932b5..d27f3b60ff6d 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -650,19 +650,22 @@ static int __dev_map_hash_update_elem(struct net *net, struct bpf_map *map,
 	u32 ifindex = *(u32 *)value;
 	u32 idx = *(u32 *)key;
 	unsigned long flags;
+	int err = -EEXIST;
 
 	if (unlikely(map_flags > BPF_EXIST || !ifindex))
 		return -EINVAL;
 
+	spin_lock_irqsave(&dtab->index_lock, flags);
+
 	old_dev = __dev_map_hash_lookup_elem(map, idx);
 	if (old_dev && (map_flags & BPF_NOEXIST))
-		return -EEXIST;
+		goto out_err;
 
 	dev = __dev_map_alloc_node(net, dtab, ifindex, idx);
-	if (IS_ERR(dev))
-		return PTR_ERR(dev);
-
-	spin_lock_irqsave(&dtab->index_lock, flags);
+	if (IS_ERR(dev)) {
+		err = PTR_ERR(dev);
+		goto out_err;
+	}
 
 	if (old_dev) {
 		hlist_del_rcu(&old_dev->index_hlist);
@@ -683,6 +686,10 @@ static int __dev_map_hash_update_elem(struct net *net, struct bpf_map *map,
 		call_rcu(&old_dev->rcu, __dev_map_entry_free);
 
 	return 0;
+
+out_err:
+	spin_unlock_irqrestore(&dtab->index_lock, flags);
+	return err;
 }
 
 static int dev_map_hash_update_elem(struct bpf_map *map, void *key, void *value,
-- 
2.23.0


^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: [PATCH bpf-next] xdp: Fix race in dev_map_hash_update_elem() when replacing element
  2019-09-08  8:20 ` [PATCH bpf-next] xdp: Fix race in dev_map_hash_update_elem() when replacing element Toke Høiland-Jørgensen
@ 2019-09-08  8:33   ` Toke Høiland-Jørgensen
  0 siblings, 0 replies; 2+ messages in thread
From: Toke Høiland-Jørgensen @ 2019-09-08  8:33 UTC (permalink / raw)
  To: make-wifi-fast, linux-wireless

Toke Høiland-Jørgensen <toke@redhat.com> writes:

> syzbot found a crash in dev_map_hash_update_elem(), when replacing an
> element with a new one. Jesper correctly identified the cause of the crash
> as a race condition between the initial lookup in the map (which is done
> before taking the lock), and the removal of the old element.
>
> Rather than just add a second lookup into the hashmap after taking the
> lock, fix this by reworking the function logic to take the lock before the
> initial lookup.
>
> Fixes: 6f9d451ab1a3 ("xdp: Add devmap_hash map type for looking up devices by hashed index")
> Reported-and-tested-by: syzbot+4e7a85b1432052e8d6f8@syzkaller.appspotmail.com
> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
> ---

Oops, this wasn't supposed to go to linux-wireless and make-wifi-fast;
apologies for the noise! :)

-Toke

^ permalink raw reply	[flat|nested] 2+ messages in thread

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2019-09-08  8:20 ` [PATCH bpf-next] xdp: Fix race in dev_map_hash_update_elem() when replacing element Toke Høiland-Jørgensen
2019-09-08  8:33   ` Toke Høiland-Jørgensen

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