In the Linux kernel, the following vulnerability has been resolved: rxrpc: Fix the ACK parser to...

In the Linux kernel, the following vulnerability has been resolved:

rxrpc: Fix the ACK parser to extract the SACK table for parsing

Fix modification of the received skbuff in rxrpc_input_soft_acks() and a
potential incorrect access of the buffer in a fragmented UDP packet (the
packet would probably have to be deliberately pre-generated as fragmented)
when AF_RXRPC tries to extract the contents of the SACK table by copying
out the contents of the SACK table into a buffer before attempting to parse

AF_RXRPC assumes that it can just call skb_condense() and then validly
access the SACK table from skb->data and that it will be a flat buffer -
but skb_condense() can silently fail to do anything under some
circumstances.

Note that whilst rxrpc_input_soft_acks() should be able to parse extended
ACKs, the rest of AF_RXRPC doesn't currently support that.

Further, there's then no need to call skb_condense() in rxrpc_input_ack(),
so don't.