net: neighbor: fix a crash caused by mod zero

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 uses prandom_u32_max() to get a random delay instead
which avoids potential division by zero.

Signed-off-by: weichenchen <weichen.chen@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 9500d28a43b0e1a390382912b6fb59db935e727b..277ed854aef1c362df96bedfa19b07ef1b6d6b80 100644 (file)
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1569,10 +1569,8 @@ 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);