On 10.07.2015 16:49, Eric Dumazet wrote:
On Fri, 2015-07-10 at 14:51 +0300, Konstantin Khlebnikov wrote:
This fixes race between non-atomic updates of adjacent bit-fields:
skb->cloned could be lost because netlink broadcast clones skb after
sending it to the first listener who sets skb->peeked at the same skb.
As a result atomic refcounting of skb header stays disabled and
skb_release_data() frees it twice. Race leads to double-free in kmalloc-xxx.
Signed-off-by: Konstantin Khlebnikov <khlebni...@yandex-team.ru>
Fixes: b19372273164 ("net: reorganize sk_buff for faster __copy_skb_header()")
---
net/netlink/af_netlink.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index dea925388a5b..921e0d8dfe3a 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2028,6 +2028,12 @@ int netlink_broadcast_filtered(struct sock *ssk, struct
sk_buff *skb, u32 portid
info.tx_filter = filter;
info.tx_data = filter_data;
+ /* Enable atomic refcounting in skb_release_data() before first send:
+ * non-atomic set of that bit-field in __skb_clone() could race with
+ * __skb_recv_datagram() which touches the same set of bit-fields.
+ */
+ skb->cloned = 1;
+
/* While we sleep in clone, do not allow to change socket list */
netlink_lock_table();
Wow, this is tricky.
I wonder how you found this bug ????
In some setups race happens quite often: once or twice per hour.
I guess the main trigger was the openvswitch which generates a
lot of netlink traffic. Though debugging was a real pain.
Acked-by: Eric Dumazet <eduma...@google.com>
--
Konstantin
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