[PATCH ipsec] xfrm: avoid wrapping AEVENT timer thresholds

[Yingjie Wang <flashhhhha@gmail.com>]

net->xfrm.sysctl_aevent_etime is stored in 100ms units, but the
conversion in xfrm_state_construct() multiplies it by HZ while it is
still a u32. Large values can wrap before the division by
XFRM_AE_ETH_M, disabling the replay timer or turning a long threshold
into a short delay.

Do the conversion in u64 and clamp the resulting jiffies value to the
range representable by replay_maxage and safe for jiffies comparisons.
Use div_u64() so 32-bit builds do not require compiler runtime helpers
for the u64 division. Use widened arithmetic when reporting
XFRMA_ETIMER_THRESH as well, so large stored values do not wrap during
readback.

On x86-64 with HZ=1000, setting xfrm_aevent_etime to 536870912 made
XFRMA_ETIMER_THRESH read back as 0 on the base kernel and 42949672 with
this fix. A normal value of 8 read back as 8 on both kernels.

Fixes: d51d081d6504 ("[IPSEC]: Sync series - user")
Cc: stable@vger.kernel.org
Signed-off-by: Yingjie Wang <flashhhhha@gmail.com>
---
 net/xfrm/xfrm_user.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index a5fbe38839c4..4a676a6aa53e 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -924,6 +924,14 @@ static void xfrm_smark_init(struct nlattr **attrs, struct xfrm_mark *m)
 	}
 }
 
+static u32 xfrm_aevent_etime_to_jiffies(u32 etime)
+{
+	u64 maxage = min_t(u64, U32_MAX, MAX_JIFFY_OFFSET);
+	u64 j = div_u64((u64)etime * HZ, XFRM_AE_ETH_M);
+
+	return min_t(u64, j, maxage);
+}
+
 static struct xfrm_state *xfrm_state_construct(struct net *net,
 					       struct xfrm_usersa_info *p,
 					       struct nlattr **attrs,
@@ -1022,7 +1030,8 @@ static struct xfrm_state *xfrm_state_construct(struct net *net,
 	x->km.seq = p->seq;
 	x->replay_maxdiff = net->xfrm.sysctl_aevent_rseqth;
 	/* sysctl_xfrm_aevent_etime is in 100ms units */
-	x->replay_maxage = (net->xfrm.sysctl_aevent_etime*HZ)/XFRM_AE_ETH_M;
+	x->replay_maxage =
+		xfrm_aevent_etime_to_jiffies(net->xfrm.sysctl_aevent_etime);
 
 	if ((err = xfrm_init_replay(x, extack)))
 		goto error;
@@ -2782,8 +2791,10 @@ static int build_aevent(struct sk_buff *skb, struct xfrm_state *x, const struct
 			goto out_cancel;
 	}
 	if (id->flags & XFRM_AE_ETHR) {
+		u64 etime = div_u64((u64)x->replay_maxage * XFRM_AE_ETH_M, HZ);
+
 		err = nla_put_u32(skb, XFRMA_ETIMER_THRESH,
-				  x->replay_maxage * 10 / HZ);
+				  min_t(u64, etime, U32_MAX));
 		if (err)
 			goto out_cancel;
 	}
-- 
2.43.0