The fragmentation code was replaced in 9b3eab61754d74a93c9840c296013fe3b4a1b606 ("batman-adv: Receive fragmented packets and merge"). The new code provided a mostly unused parameter skb for the merging function. It is used inside the function to calculate the additionally needed skb tailroom. But instead of increasing its own tailroom, it is only increasing the tailroom of the first queued skb. This is not correct in most situations because the first queued entry can be a different one than the parameter.
An observed problem was:
1. packet with size 104, total_size 1464, fragno 1 was received - packet is queued 2. packet with size 1400, total_size 1464, fragno 0 was received - packet is queued at the end of the list 3. enough data was received and can be given to the merge function (1464 == (1400 - 20) + (104 - 20)) - merge functions gets 1400 byte large packet as skb argument 4. merge function gets first entry in queue (104 byte) - stored as skb_out 5. merge function calculates the required extra tail as total_size - skb->len - pskb_expand_head tail of skb_out with 64 bytes 6. merge function tries to squeeze the extra 1380 bytes from the second queued skb (1400 byte aka skb parameter) in the 64 extra tail bytes of skb_out
Instead calculate the extra required tail bytes for skb_out also using skb_out instead of using the parameter skb. The skb parameter is only used to get the total_size from the last received packet. This is also the total_size used to decide that all fragments were received.
Signed-off-by: Sven Eckelmann sven@narfation.org Reported-by: Philipp Psurek philipp.psurek@gmail.com --- This is a minimized version which doesn't require the patch "[PATCH-maint] batman-adv: Check total_size when reassembling fragments".
It is only compile tested --- fragmentation.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fragmentation.c b/fragmentation.c index f14e54a..af16844 100644 --- a/fragmentation.c +++ b/fragmentation.c @@ -247,7 +247,7 @@ batadv_frag_merge_packets(struct hlist_head *chain, struct sk_buff *skb) kfree(entry);
/* Make room for the rest of the fragments. */ - if (pskb_expand_head(skb_out, 0, size - skb->len, GFP_ATOMIC) < 0) { + if (pskb_expand_head(skb_out, 0, size - skb_out->len, GFP_ATOMIC) < 0) { kfree_skb(skb_out); skb_out = NULL; goto free;