Hello Edward Cree,
The patch 7da517a3bc52: "net: core: Another step of skb receive list
processing" from Jul 2, 2018, leads to the following static checker
warning:
net/core/dev.c:5001 netif_receive_skb_list_internal()
warn: 'skb' was already freed.
The patch 17266ee93984: "net: ipv4: listified version of ip_rcv" from
Jul 2, 2018, leads to the following static checker warning:
./include/linux/netfilter.h:301 NF_HOOK_LIST()
warn: 'skb' was already freed.
net/core/dev.c
4982 static void netif_receive_skb_list_internal(struct list_head *head)
4983 {
4984 struct bpf_prog *xdp_prog = NULL;
4985 struct sk_buff *skb, *next;
4986
4987 list_for_each_entry_safe(skb, next, head, list) {
4988 net_timestamp_check(netdev_tstamp_prequeue, skb);
4989 if (skb_defer_rx_timestamp(skb))
4990 /* Handled, remove from list */
4991 list_del(&skb->list);
4992 }
4993
4994 if (static_branch_unlikely(&generic_xdp_needed_key)) {
4995 preempt_disable();
4996 rcu_read_lock();
4997 list_for_each_entry_safe(skb, next, head, list) {
4998 xdp_prog = rcu_dereference(skb->dev->xdp_prog);
4999 if (do_xdp_generic(xdp_prog, skb) != XDP_PASS)
5000 /* Dropped, remove from list */
5001 list_del(&skb->list);
do_xdp_generic() frees skb.
5002 }
5003 rcu_read_unlock();
5004 preempt_enable();
5005 }
./include/linux/netfilter.h
291 static inline void
292 NF_HOOK_LIST(uint8_t pf, unsigned int hook, struct net *net, struct
sock *sk,
293 struct list_head *head, struct net_device *in, struct
net_device *out,
294 int (*okfn)(struct net *, struct sock *, struct sk_buff *))
295 {
296 struct sk_buff *skb, *next;
297
298 list_for_each_entry_safe(skb, next, head, list) {
299 int ret = nf_hook(pf, hook, net, sk, skb, in, out,
okfn);
300 if (ret != 1)
301 list_del(&skb->list);
For this one Smatch thinks that nf_hook() sometimes frees skb, but the
code is less clear to me than for the previous warning so I don't know.
302 }
303 }
regards,
dan carpenter
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