Re: [PATCH net] ipvs: reject negative sync_refresh_period values

[Julian Anastasov]

	Hello,

On Mon, 2 Nov 2026, Yingjie Wang wrote:

> 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>
> ---
>  include/net/ip_vs.h            | 7 ++++---
>  net/netfilter/ipvs/ip_vs_ctl.c | 8 ++++++--
>  2 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/include/net/ip_vs.h b/include/net/ip_vs.h
> index 9a83bff32569..66f26c3d1f75 100644
> --- a/include/net/ip_vs.h
> +++ b/include/net/ip_vs.h
> @@ -19,6 +19,7 @@
>  
>  #include <linux/compiler.h>
>  #include <linux/timer.h>
> +#include <linux/jiffies.h>

	This is not needed. The remaining part looks ok. Prefer
to use "nf" tag for IPVS patches.

>  #include <linux/bug.h>
>  
>  #include <net/checksum.h>
> @@ -1267,7 +1268,7 @@ 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 +1336,7 @@ 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 +1364,7 @@ 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,

	It is sad that there is no proc_dointvec_jiffies_minmax

> +		.extra1		= SYSCTL_ZERO,
> +		.extra2		= &sync_refresh_period_max,
>  	},
>  	{
>  		.procname	= "sync_retries",
> 
> base-commit: cb284914e749388eef402938bdb3115fe1f6d337
> -- 
> 2.43.0

Regards

--
Julian Anastasov <ja@xxxxxx>