| Message ID | 20190908082016.17214-1-toke@redhat.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | Johannes Berg |
| Headers | show |
| Series | [bpf-next] xdp: Fix race in dev_map_hash_update_elem() when replacing element | expand |
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
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,
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(-)