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.c...@linux.alibaba.com>
---
V4:
- Use prandom_u32_max() to get a random delay in
pneigh_enqueue().
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.
V4 is quite concise and works well.
Thanks for Eric's and Jakub's advice.
---
net/core/neighbour.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 9500d28a43b0..277ed854aef1 100644
--- 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);
--
2.20.1 (Apple Git-117)
