| Message ID | 20201222123838.12951-1-weichen.chen@linux.alibaba.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [v3] net: neighbor: fix a crash caused by mod zero | expand |
On 12/22/20 1:38 PM, weichenchen wrote: > pneigh_enqueue() tries to obtain a random delay by mod > NEIGH_VAR(p, PROXY_DELAY). However, NEIGH_VAR(p, PROXY_DELAY) > migth be zero at that point because someone could write zero > to /proc/sys/net/ipv4/neigh/[device]/proxy_delay after the > callers check it. > > This patch makes pneigh_enqueue() get a delay time passed in > by the callers and the callers guarantee it is not zero. > > Signed-off-by: weichenchen <weichen.chen@linux.alibaba.com> > --- > V3: > - Callers need to pass the delay time to pneigh_enqueue() > now and they should guarantee it is not zero. > - Use READ_ONCE() to read NEIGH_VAR(p, PROXY_DELAY) in both > of the existing callers of pneigh_enqueue() and then pass > it to pneigh_enqueue(). > V2: > - Use READ_ONCE() to prevent the complier from re-reading > NEIGH_VAR(p, PROXY_DELAY). > - Give a hint to the complier that delay <= 0 is unlikely > to happen. > --- > include/net/neighbour.h | 2 +- > net/core/neighbour.c | 5 ++--- > net/ipv4/arp.c | 8 +++++--- > net/ipv6/ndisc.c | 6 +++--- > 4 files changed, 11 insertions(+), 10 deletions(-) > > diff --git a/include/net/neighbour.h b/include/net/neighbour.h > index 22ced1381ede..f7564dc5304d 100644 > --- a/include/net/neighbour.h > +++ b/include/net/neighbour.h > @@ -352,7 +352,7 @@ struct net *neigh_parms_net(const struct neigh_parms *parms) > unsigned long neigh_rand_reach_time(unsigned long base); > > void pneigh_enqueue(struct neigh_table *tbl, struct neigh_parms *p, > - struct sk_buff *skb); > + struct sk_buff *skb, int delay); > struct pneigh_entry *pneigh_lookup(struct neigh_table *tbl, struct net *net, > const void *key, struct net_device *dev, > int creat); > diff --git a/net/core/neighbour.c b/net/core/neighbour.c > index 9500d28a43b0..b440f966d109 100644 > --- a/net/core/neighbour.c > +++ b/net/core/neighbour.c > @@ -1567,12 +1567,11 @@ static void neigh_proxy_process(struct timer_list *t) > } > > void pneigh_enqueue(struct neigh_table *tbl, struct neigh_parms *p, > - struct sk_buff *skb) > + struct sk_buff *skb, int delay) > { > unsigned long now = jiffies; > > - unsigned long sched_next = now + (prandom_u32() % > - NEIGH_VAR(p, PROXY_DELAY)); > + unsigned long sched_next = now + (prandom_u32() % delay); > > if (tbl->proxy_queue.qlen > NEIGH_VAR(p, PROXY_QLEN)) { > kfree_skb(skb); This seems rather complex, what about not using a divide in the first place ? : diff --git a/net/core/neighbour.c b/net/core/neighbour.c index 9500d28a43b0e1a390382912b6fb59db935e727b..745bc89acc87c2a4802fb6f301c11edd2f0096da 100644 --- a/net/core/neighbour.c +++ b/net/core/neighbour.c @@ -1569,10 +1569,7 @@ static void neigh_proxy_process(struct timer_list *t) void pneigh_enqueue(struct neigh_table *tbl, struct neigh_parms *p, struct sk_buff *skb) { - unsigned long now = jiffies; - - unsigned long sched_next = now + (prandom_u32() % - NEIGH_VAR(p, PROXY_DELAY)); + unsigned long sched_next = jiffies + prandom_u32_max(NEIGH_VAR(p, PROXY_DELAY)); if (tbl->proxy_queue.qlen > NEIGH_VAR(p, PROXY_QLEN)) { kfree_skb(skb);
diff --git a/include/net/neighbour.h b/include/net/neighbour.h index 22ced1381ede..f7564dc5304d 100644 --- a/include/net/neighbour.h +++ b/include/net/neighbour.h @@ -352,7 +352,7 @@ struct net *neigh_parms_net(const struct neigh_parms *parms) unsigned long neigh_rand_reach_time(unsigned long base); void pneigh_enqueue(struct neigh_table *tbl, struct neigh_parms *p, - struct sk_buff *skb); + struct sk_buff *skb, int delay); struct pneigh_entry *pneigh_lookup(struct neigh_table *tbl, struct net *net, const void *key, struct net_device *dev, int creat); diff --git a/net/core/neighbour.c b/net/core/neighbour.c index 9500d28a43b0..b440f966d109 100644 --- a/net/core/neighbour.c +++ b/net/core/neighbour.c @@ -1567,12 +1567,11 @@ static void neigh_proxy_process(struct timer_list *t) } void pneigh_enqueue(struct neigh_table *tbl, struct neigh_parms *p, - struct sk_buff *skb) + struct sk_buff *skb, int delay) { unsigned long now = jiffies; - unsigned long sched_next = now + (prandom_u32() % - NEIGH_VAR(p, PROXY_DELAY)); + unsigned long sched_next = now + (prandom_u32() % delay); if (tbl->proxy_queue.qlen > NEIGH_VAR(p, PROXY_QLEN)) { kfree_skb(skb); diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c index 922dd73e5740..6ddce6e0a648 100644 --- a/net/ipv4/arp.c +++ b/net/ipv4/arp.c @@ -841,20 +841,22 @@ static int arp_process(struct net *net, struct sock *sk, struct sk_buff *skb) arp_fwd_pvlan(in_dev, dev, rt, sip, tip) || (rt->dst.dev != dev && pneigh_lookup(&arp_tbl, net, &tip, dev, 0)))) { + int delay; + n = neigh_event_ns(&arp_tbl, sha, &sip, dev); if (n) neigh_release(n); + delay = READ_ONCE(NEIGH_VAR(in_dev->arp_parms, PROXY_DELAY)); if (NEIGH_CB(skb)->flags & LOCALLY_ENQUEUED || - skb->pkt_type == PACKET_HOST || - NEIGH_VAR(in_dev->arp_parms, PROXY_DELAY) == 0) { + skb->pkt_type == PACKET_HOST || delay == 0) { arp_send_dst(ARPOP_REPLY, ETH_P_ARP, sip, dev, tip, sha, dev->dev_addr, sha, reply_dst); } else { pneigh_enqueue(&arp_tbl, - in_dev->arp_parms, skb); + in_dev->arp_parms, skb, delay); goto out_free_dst; } goto out_consume_skb; diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c index 76717478f173..efdaaab47535 100644 --- a/net/ipv6/ndisc.c +++ b/net/ipv6/ndisc.c @@ -892,10 +892,10 @@ static void ndisc_recv_ns(struct sk_buff *skb) (idev->cnf.forwarding && (net->ipv6.devconf_all->proxy_ndp || idev->cnf.proxy_ndp) && (is_router = pndisc_is_router(&msg->target, dev)) >= 0)) { + int delay = READ_ONCE(NEIGH_VAR(idev->nd_parms, PROXY_DELAY)); if (!(NEIGH_CB(skb)->flags & LOCALLY_ENQUEUED) && skb->pkt_type != PACKET_HOST && - inc && - NEIGH_VAR(idev->nd_parms, PROXY_DELAY) != 0) { + inc && delay != 0) { /* * for anycast or proxy, * sender should delay its response @@ -905,7 +905,7 @@ static void ndisc_recv_ns(struct sk_buff *skb) */ struct sk_buff *n = skb_clone(skb, GFP_ATOMIC); if (n) - pneigh_enqueue(&nd_tbl, idev->nd_parms, n); + pneigh_enqueue(&nd_tbl, idev->nd_parms, n, delay); goto out; } } else
pneigh_enqueue() tries to obtain a random delay by mod NEIGH_VAR(p, PROXY_DELAY). However, NEIGH_VAR(p, PROXY_DELAY) migth be zero at that point because someone could write zero to /proc/sys/net/ipv4/neigh/[device]/proxy_delay after the callers check it. This patch makes pneigh_enqueue() get a delay time passed in by the callers and the callers guarantee it is not zero. Signed-off-by: weichenchen <weichen.chen@linux.alibaba.com> --- V3: - Callers need to pass the delay time to pneigh_enqueue() now and they should guarantee it is not zero. - Use READ_ONCE() to read NEIGH_VAR(p, PROXY_DELAY) in both of the existing callers of pneigh_enqueue() and then pass it to pneigh_enqueue(). V2: - Use READ_ONCE() to prevent the complier from re-reading NEIGH_VAR(p, PROXY_DELAY). - Give a hint to the complier that delay <= 0 is unlikely to happen. --- include/net/neighbour.h | 2 +- net/core/neighbour.c | 5 ++--- net/ipv4/arp.c | 8 +++++--- net/ipv6/ndisc.c | 6 +++--- 4 files changed, 11 insertions(+), 10 deletions(-)