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xdp: Fix race in dev_map_hash_update_elem() when replacing element

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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: 6f9d451ab1 ("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>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Toke Høiland-Jørgensen 2019-09-08 09:20:16 +01:00 committed by Daniel Borkmann
parent a4fa6e1690
commit af58e7ee6a
1 changed files with 12 additions and 5 deletions
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17
kernel/bpf/devmap.c
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@ -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,