net: Clone skb before setting peeked flag
commit
738ac1ebb96d02e0d23bc320302a6ea94c612dec upstream.
Shared skbs must not be modified and this is crucial for broadcast
and/or multicast paths where we use it as an optimisation to avoid
unnecessary cloning.
The function skb_recv_datagram breaks this rule by setting peeked
without cloning the skb first. This causes funky races which leads
to double-free.
This patch fixes this by cloning the skb and replacing the skb
in the list when setting skb->peeked.
Fixes:
a59322be07c9 ("[UDP]: Only increment counter on first peek/recv")
Reported-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>