| Message ID | 20201221130754.12628-1-weichen.chen@linux.alibaba.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] net: neighbor: fix a crash caused by mod zero | expand |
diff --git a/net/core/neighbour.c b/net/core/neighbour.c index 9500d28a43b0..7b03d3f129c0 100644 --- a/net/core/neighbour.c +++ b/net/core/neighbour.c @@ -1570,9 +1570,14 @@ void pneigh_enqueue(struct neigh_table *tbl, struct neigh_parms *p, struct sk_buff *skb) { unsigned long now = jiffies; + unsigned long sched_next; - unsigned long sched_next = now + (prandom_u32() % - NEIGH_VAR(p, PROXY_DELAY)); + int delay = READ_ONCE(NEIGH_VAR(p, PROXY_DELAY)); + + if (unlikely(delay <= 0)) + sched_next = now; + else + sched_next = now + (prandom_u32() % delay); if (tbl->proxy_queue.qlen > NEIGH_VAR(p, PROXY_QLEN)) { kfree_skb(skb);
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 double-checks NEIGH_VAR(p, PROXY_DELAY) in pneigh_enqueue() to ensure not to take zero as modulus. Signed-off-by: weichenchen <weichen.chen@linux.alibaba.com> --- 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. Note: I don't think having the caller pass in the value is a good idea mainly because delay should be only decided by /proc/sys/net/ipv4/neigh/[device]/proxy_delay rather than the caller. --- net/core/neighbour.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)