[PATCH 2/2] time/jiffies: Saturate in mult_hz() instead of wrapping

[Zhan Xusheng]

mult_hz() converts a user-supplied seconds value to jiffies for
proc_dointvec_jiffies().  proc_int_u2k_conv_uop() rejects a result above
INT_MAX, but it inspects the product, so a product that wraps arrives as a
small value and is stored:

	# echo 18446744073709552 > /proc/sys/net/ipv4/tcp_keepalive_time
	# cat /proc/sys/net/ipv4/tcp_keepalive_time
	0

One less is rejected; that value wraps to 384 jiffies at HZ=1000.  65
sysctls use proc_dointvec_jiffies(), among them tcp_keepalive_time,
tcp_fin_timeout and the conntrack timeouts.

Bound the input in the shape clock_t_to_jiffies() already uses and leave
the INT_MAX policy to the caller.  The bound was open-coded as
"*lvalp > INT_MAX / HZ" until commit 2dc164a48e6f ("sysctl: Create
converter functions with two new macros").

Fixes: 2dc164a48e6f ("sysctl: Create converter functions with two new macros")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Zhan Xusheng <zhanxusheng@xxxxxxxxxx>
---
 kernel/time/jiffies.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
index 80c354811538..9b3487d40cd6 100644
--- a/kernel/time/jiffies.c
+++ b/kernel/time/jiffies.c
@@ -101,6 +101,8 @@ void __init register_refined_jiffies(long cycles_per_second)
 #ifdef CONFIG_SYSCTL
 static ulong mult_hz(const ulong val)
 {
+	if (val >= ULONG_MAX / HZ)
+		return ULONG_MAX;
 	return val * HZ;
 }
 
-- 
2.43.0