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__netif_receive_skb_core: pass skb by reference
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__netif_receive_skb_core may change the skb pointer passed into it (e.g.
in rx_handler). The original skb may be freed as a result of this
operation.

The callers of __netif_receive_skb_core may further process original skb
by using pt_prev pointer returned by __netif_receive_skb_core thus
leading to unpleasant effects.

The solution is to pass skb by reference into __netif_receive_skb_core.

v2: Added Fixes tag and comment regarding ppt_prev and skb invariant.

Fixes: 88eb194 ("net: core: propagate SKB lists through packet_type lookup")
Signed-off-by: Boris Sukholitko <[email protected]>
Acked-by: Edward Cree <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
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Boris Sukholitko authored and davem330 committed May 19, 2020
1 parent 88d7fcf commit c0bbbdc
Showing 1 changed file with 15 additions and 5 deletions.
20 changes: 15 additions & 5 deletions net/core/dev.c
Original file line number Diff line number Diff line change
Expand Up @@ -4988,11 +4988,12 @@ static inline int nf_ingress(struct sk_buff *skb, struct packet_type **pt_prev,
return 0;
}

static int __netif_receive_skb_core(struct sk_buff *skb, bool pfmemalloc,
static int __netif_receive_skb_core(struct sk_buff **pskb, bool pfmemalloc,
struct packet_type **ppt_prev)
{
struct packet_type *ptype, *pt_prev;
rx_handler_func_t *rx_handler;
struct sk_buff *skb = *pskb;
struct net_device *orig_dev;
bool deliver_exact = false;
int ret = NET_RX_DROP;
Expand Down Expand Up @@ -5023,8 +5024,10 @@ static int __netif_receive_skb_core(struct sk_buff *skb, bool pfmemalloc,
ret2 = do_xdp_generic(rcu_dereference(skb->dev->xdp_prog), skb);
preempt_enable();

if (ret2 != XDP_PASS)
return NET_RX_DROP;
if (ret2 != XDP_PASS) {
ret = NET_RX_DROP;
goto out;
}
skb_reset_mac_len(skb);
}

Expand Down Expand Up @@ -5174,6 +5177,13 @@ static int __netif_receive_skb_core(struct sk_buff *skb, bool pfmemalloc,
}

out:
/* The invariant here is that if *ppt_prev is not NULL
* then skb should also be non-NULL.
*
* Apparently *ppt_prev assignment above holds this invariant due to
* skb dereferencing near it.
*/
*pskb = skb;
return ret;
}

Expand All @@ -5183,7 +5193,7 @@ static int __netif_receive_skb_one_core(struct sk_buff *skb, bool pfmemalloc)
struct packet_type *pt_prev = NULL;
int ret;

ret = __netif_receive_skb_core(skb, pfmemalloc, &pt_prev);
ret = __netif_receive_skb_core(&skb, pfmemalloc, &pt_prev);
if (pt_prev)
ret = INDIRECT_CALL_INET(pt_prev->func, ipv6_rcv, ip_rcv, skb,
skb->dev, pt_prev, orig_dev);
Expand Down Expand Up @@ -5261,7 +5271,7 @@ static void __netif_receive_skb_list_core(struct list_head *head, bool pfmemallo
struct packet_type *pt_prev = NULL;

skb_list_del_init(skb);
__netif_receive_skb_core(skb, pfmemalloc, &pt_prev);
__netif_receive_skb_core(&skb, pfmemalloc, &pt_prev);
if (!pt_prev)
continue;
if (pt_curr != pt_prev || od_curr != orig_dev) {
Expand Down

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