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net: Clone skb before setting peeked flag

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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: a59322be07 ("[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>
This commit is contained in:
Herbert Xu 2015-07-13 16:04:13 +08:00 committed by David S. Miller
parent 035d210f92
commit 738ac1ebb9
1 changed files with 38 additions and 3 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

41
net/core/datagram.c
View file

@ -131,6 +131,35 @@ static int wait_for_more_packets(struct sock *sk, int *err, long *timeo_p,
goto out;
}
static int skb_set_peeked(struct sk_buff *skb)
{
struct sk_buff *nskb;
if (skb->peeked)
return 0;
/* We have to unshare an skb before modifying it. */
if (!skb_shared(skb))
goto done;
nskb = skb_clone(skb, GFP_ATOMIC);
if (!nskb)
return -ENOMEM;
skb->prev->next = nskb;
skb->next->prev = nskb;
nskb->prev = skb->prev;
nskb->next = skb->next;
consume_skb(skb);
skb = nskb;
done:
skb->peeked = 1;
return 0;
}
/**
* __skb_recv_datagram - Receive a datagram skbuff
* @sk: socket
@ -165,7 +194,9 @@ static int wait_for_more_packets(struct sock *sk, int *err, long *timeo_p,
struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags,
int *peeked, int *off, int *err)
{
struct sk_buff_head *queue = &sk->sk_receive_queue;
struct sk_buff *skb, *last;
unsigned long cpu_flags;
long timeo;
/*
* Caller is allowed not to check sk->sk_err before skb_recv_datagram()
@ -184,8 +215,6 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags,
* Look at current nfs client by the way...
* However, this function was correct in any case. 8)
*/
unsigned long cpu_flags;
struct sk_buff_head *queue = &sk->sk_receive_queue;
int _off = *off;
last = (struct sk_buff *)queue;
@ -199,7 +228,11 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags,
_off -= skb->len;
continue;
}
skb->peeked = 1;
error = skb_set_peeked(skb);
if (error)
goto unlock_err;
atomic_inc(&skb->users);
} else
__skb_unlink(skb, queue);
@ -223,6 +256,8 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags,
return NULL;
unlock_err:
spin_unlock_irqrestore(&queue->lock, cpu_flags);
no_packet:
*err = error;
return NULL;