batman-adv: Fix double free during fragment merge error

commit 248e23b50e2da0753f3b5faa068939cbe9f8a75a upstream.

The function batadv_frag_skb_buffer was supposed not to consume the skbuff
on errors. This was followed in the helper function
batadv_frag_insert_packet when the skb would potentially be inserted in the
fragment queue. But it could happen that the next helper function
batadv_frag_merge_packets would try to merge the fragments and fail. This
results in a kfree_skb of all the enqueued fragments (including the just
inserted one). batadv_recv_frag_packet would detect the error in
batadv_frag_skb_buffer and try to free the skb again.

The behavior of batadv_frag_skb_buffer (and its helper
batadv_frag_insert_packet) must therefore be changed to always consume the
skbuff to have a common behavior and avoid the double kfree_skb.

Fixes: 610bfc6bc99b ("batman-adv: Receive fragmented packets and merge")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
[bwh: Backported to 3.16:
 - Update batadv_recv_frag_packet() as advised by Sven
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/batman-adv/fragmentation.c b/net/batman-adv/fragmentation.c
index d2b6d5066c3388b7db369d9df9b6132675997d7b..ab95235d738ad67f7a30a5e0bacd9fbe23731b47 100644 (file)
--- a/net/batman-adv/fragmentation.c
+++ b/net/batman-adv/fragmentation.c
@@ -212,8 +212,10 @@ err_unlock:
        spin_unlock_bh(&chain->lock);
 
 err:
-       if (!ret)
+       if (!ret) {
                kfree(frag_entry_new);
+               kfree_skb(skb);
+       }
 
        return ret;
 }
@@ -288,7 +290,7 @@ free:
  *
  * There are three possible outcomes: 1) Packet is merged: Return true and
  * set *skb to merged packet; 2) Packet is buffered: Return true and set *skb
- * to NULL; 3) Error: Return false and leave skb as is.
+ * to NULL; 3) Error: Return false and free skb.
  */
 bool batadv_frag_skb_buffer(struct sk_buff **skb,
                            struct batadv_orig_node *orig_node_src)
@@ -310,9 +312,9 @@ bool batadv_frag_skb_buffer(struct sk_buff **skb,
                goto out_err;
 
 out:
-       *skb = skb_out;
        ret = true;
 out_err:
+       *skb = skb_out;
        return ret;
 }
 

diff --git a/net/batman-adv/routing.c b/net/batman-adv/routing.c
index 34c20cc0670c9773d21ab0b49c2d73a7759a316a..7a1032348ea9f90bf8d5d213128ff524c35f3db6 100644 (file)
--- a/net/batman-adv/routing.c
+++ b/net/batman-adv/routing.c
@@ -1025,6 +1025,12 @@ int batadv_recv_frag_packet(struct sk_buff *skb,
        batadv_inc_counter(bat_priv, BATADV_CNT_FRAG_RX);
        batadv_add_counter(bat_priv, BATADV_CNT_FRAG_RX_BYTES, skb->len);
 
+       /* batadv_frag_skb_buffer will always consume the skb and
+        * the caller should therefore never try to free the
+        * skb after this point
+        */
+       ret = NET_RX_SUCCESS;
+
        /* Add fragment to buffer and merge if possible. */
        if (!batadv_frag_skb_buffer(&skb, orig_node_src))
                goto out;
@@ -1036,8 +1042,6 @@ int batadv_recv_frag_packet(struct sk_buff *skb,
                batadv_batman_skb_recv(skb, recv_if->net_dev,
                                       &recv_if->batman_adv_ptype, NULL);
 
-       ret = NET_RX_SUCCESS;
-
 out:
        if (orig_node_src)
                batadv_orig_node_free_ref(orig_node_src);