Commit 2482787e authored by Herbert Xu's avatar Herbert Xu Committed by Greg Kroah-Hartman

net: Clone skb before setting peeked flag

[ Upstream commit 738ac1eb ]

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: a59322be ("[UDP]: Only increment counter on first peek/recv")
Reported-by: default avatarKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 69f02461
......@@ -130,6 +130,35 @@ 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
......@@ -164,7 +193,9 @@ 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()
......@@ -183,8 +214,6 @@ 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;
......@@ -198,7 +227,11 @@ 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);
......@@ -222,6 +255,8 @@ 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;
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment