Re: [PATCH] ipvs: fix racy memcpy in proc_do_sync_threshold

[Simon Horman <horms@xxxxxxxxxx>]

On Thu, Aug 10, 2023 at 03:12:42PM -0400, Sishuai Gong wrote:

+ Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
  Florian Westphal <fw@xxxxxxxxx>
  Jozsef Kadlecsik <kadlec@xxxxxxxxxxxxx>
  netfilter-devel@xxxxxxxxxxxxxxx
  coreteam@xxxxxxxxxxxxx

> When two threads run proc_do_sync_threshold() in parallel,
> data races could happen between the two memcpy():
> 
> Thread-1                      Thread-2
> memcpy(val, valp, sizeof(val));
>                               memcpy(valp, val, sizeof(val));
> 
> This race might mess up the (struct ctl_table *) table->data,
> so we add a mutex lock to serilize them, as discussed in [1].
> 
> [1] 
> https://archive.linuxvirtualserver.org/html/lvs-devel/2023-08/msg00031.html
> 
> Signed-off-by: Sishuai Gong <sishuai.system@xxxxxxxxx>

Probably this is a fix for nf and should have:

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")

In any case, this change looks good to me.

Acked-by: Simon Horman <horms@xxxxxxxxxx>

> ---
>  net/netfilter/ipvs/ip_vs_ctl.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
> index 62606fb44d02..4bb0d90eca1c 100644
> --- a/net/netfilter/ipvs/ip_vs_ctl.c
> +++ b/net/netfilter/ipvs/ip_vs_ctl.c
> @@ -1876,6 +1876,7 @@ static int
>  proc_do_sync_threshold(struct ctl_table *table, int write,
>                      void *buffer, size_t *lenp, loff_t *ppos)
>  {
> +     struct netns_ipvs *ipvs = table->extra2;
>       int *valp = table->data;
>       int val[2];
>       int rc;
> @@ -1885,6 +1886,7 @@ proc_do_sync_threshold(struct ctl_table *table, int 
> write,
>               .mode = table->mode,
>       };
>  
> +     mutex_lock(&ipvs->sync_mutex);
>       memcpy(val, valp, sizeof(val));
>       rc = proc_dointvec(&tmp, write, buffer, lenp, ppos);
>       if (write) {
> @@ -1894,6 +1896,7 @@ proc_do_sync_threshold(struct ctl_table *table, int 
> write,
>               else
>                       memcpy(valp, val, sizeof(val));
>       }
> +     mutex_unlock(&ipvs->sync_mutex);
>       return rc;
>  }
>  
> @@ -4321,6 +4324,7 @@ static int __net_init 
> ip_vs_control_net_init_sysctl(struct netns_ipvs *ipvs)
>       ipvs->sysctl_sync_threshold[0] = DEFAULT_SYNC_THRESHOLD;
>       ipvs->sysctl_sync_threshold[1] = DEFAULT_SYNC_PERIOD;
>       tbl[idx].data = &ipvs->sysctl_sync_threshold;
> +     tbl[idx].extra2 = ipvs;
>       tbl[idx++].maxlen = sizeof(ipvs->sysctl_sync_threshold);
>       ipvs->sysctl_sync_refresh_period = DEFAULT_SYNC_REFRESH_PERIOD;
>       tbl[idx++].data = &ipvs->sysctl_sync_refresh_period;
> -- 
> 2.39.2 (Apple Git-143)
>