[PATCH nf v2] ipvs: reject negative sync_refresh_period values

[Yingjie Wang]

net.ipv4.vs.sync_refresh_period is documented as an unsigned number of
seconds.  proc_dointvec_jiffies() accepts a signed integer and converts
it to jiffies before storing it in an unsigned int field.  Consequently,
writing -1 stores UINT_MAX - HZ + 1 jiffies and bypasses the finite
bound applied to ordinary positive writes.

This changes the behavior of ip_vs_sync_conn_needed().  With
sync_threshold="0 1" (threshold 0, period 1) and
sync_refresh_period=-1, only the first of twelve packets requests a
sync message; the zero-refresh control requests all twelve.

Store the value in seconds, as documented, and convert it at the single
consumer.  Use proc_douintvec_minmax() to reject negative input.  Cap the
value at INT_MAX / HZ to preserve the prior jiffies range and avoid
overflow in secs_to_jiffies().

The issue was reproduced on an affected 7.0 distribution kernel in a
temporary network namespace.  A patched target kernel was built with W=1
and exercised in QEMU; -1 is now rejected with EINVAL, zero and positive
values retain their behavior, and the HZ=1000 boundary accepts 2147483
while rejecting 2147484.

Fixes: 749c42b620a9 ("ipvs: reduce sync rate with time thresholds")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Yingjie Wang <1075151112@xxxxxx>
---

Notes:
    Changes since v1:
    - Drop the unnecessary <linux/jiffies.h> include.
    - Rebase on current net/main and use the nf target tag.
    
    Link: https://lore.kernel.org/r/tencent_C567615098D5B2A71811CFE5CB09C9FFC406@xxxxxx/

 include/net/ip_vs.h            | 6 +++---
 net/netfilter/ipvs/ip_vs_ctl.c | 8 ++++++--
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/include/net/ip_vs.h b/include/net/ip_vs.h
index 9a83bff32569..b6834542489a 100644
--- a/include/net/ip_vs.h
+++ b/include/net/ip_vs.h
@@ -1267,7 +1267,7 @@ struct netns_ipvs {
 	int			sysctl_sloppy_sctp;
 	int			sysctl_expire_quiescent_template;
 	int			sysctl_sync_threshold[2];
-	unsigned int		sysctl_sync_refresh_period;
+	unsigned int		sysctl_sync_refresh_period; /* seconds */
 	int			sysctl_sync_retries;
 	int			sysctl_nat_icmp_send;
 	int			sysctl_pmtu_disc;
@@ -1335,7 +1335,7 @@ struct netns_ipvs {
 #define DEFAULT_SYNC_VER	1
 #define DEFAULT_SLOPPY_TCP	0
 #define DEFAULT_SLOPPY_SCTP	0
-#define DEFAULT_SYNC_REFRESH_PERIOD	(0U * HZ)
+#define DEFAULT_SYNC_REFRESH_PERIOD	0U
 #define DEFAULT_SYNC_RETRIES		0
 #define IPVS_SYNC_WAKEUP_RATE	8
 #define IPVS_SYNC_QLEN_MAX	(IPVS_SYNC_WAKEUP_RATE * 4)
@@ -1363,7 +1363,7 @@ static inline int sysctl_sync_period(struct netns_ipvs *ipvs)
 
 static inline unsigned int sysctl_sync_refresh_period(struct netns_ipvs *ipvs)
 {
-	return READ_ONCE(ipvs->sysctl_sync_refresh_period);
+	return secs_to_jiffies(READ_ONCE(ipvs->sysctl_sync_refresh_period));
 }
 
 static inline int sysctl_sync_retries(struct netns_ipvs *ipvs)
diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
index ce9fe20d6106..82726b6b5e3a 100644
--- a/net/netfilter/ipvs/ip_vs_ctl.c
+++ b/net/netfilter/ipvs/ip_vs_ctl.c
@@ -2369,6 +2369,8 @@ static int ip_vs_zero_all(struct netns_ipvs *ipvs)
 
 #ifdef CONFIG_SYSCTL
 
+static unsigned int sync_refresh_period_max = INT_MAX / HZ;
+
 static int
 proc_do_conn_max(const struct ctl_table *table, int write,
 		 void *buffer, size_t *lenp, loff_t *ppos)
@@ -2824,9 +2826,11 @@ static struct ctl_table vs_vars[] = {
 	},
 	{
 		.procname	= "sync_refresh_period",
-		.maxlen		= sizeof(int),
+		.maxlen		= sizeof(unsigned int),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec_jiffies,
+		.proc_handler	= proc_douintvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= &sync_refresh_period_max,
 	},
 	{
 		.procname	= "sync_retries",

base-commit: 647b81ddefc6364290e67bf33c89d54971f8995e
-- 
2.43.0