[ovs-dev] [PATCH 5/5] dpif-netlink: Fix send of uninitialized memory in ct limit requests.

[Mark Gray]

On 04/04/2021 18:31, Ilya Maximets wrote:
> ct limit requests never initializes the whole 'struct ovs_zone_limit'
> sending uninitialized stack memory to kernel:
> 
>  Syscall param sendmsg(msg.msg_iov[0]) points to uninitialised byte(s)
>     at 0x5E23867: sendmsg (in /usr/lib64/libpthread-2.28.so)
>     by 0x54F761: nl_sock_transact_multiple__ (netlink-socket.c:858)
>     by 0x54FB6E: nl_sock_transact_multiple.part.9 (netlink-socket.c:1079)
>     by 0x54FCC0: nl_sock_transact_multiple (netlink-socket.c:1044)
>     by 0x54FCC0: nl_sock_transact (netlink-socket.c:1108)
>     by 0x550B6F: nl_transact (netlink-socket.c:1804)
>     by 0x53BEA2: dpif_netlink_ct_get_limits (dpif-netlink.c:3052)
>     by 0x588B57: dpctl_ct_get_limits (dpctl.c:2178)
>     by 0x586FF2: dpctl_unixctl_handler (dpctl.c:2870)
>     by 0x52C241: process_command (unixctl.c:310)
>     by 0x52C241: run_connection (unixctl.c:344)
>     by 0x52C241: unixctl_server_run (unixctl.c:395)
>     by 0x407526: main (ovs-vswitchd.c:128)
>   Address 0x10b87480 is 32 bytes inside a block of size 4,096 alloc'd
>     at 0x4C30F0B: malloc (vg_replace_malloc.c:307)
>     by 0x52CDE4: xmalloc (util.c:138)
>     by 0x4F7E07: ofpbuf_init (ofpbuf.c:123)
>     by 0x4F7E07: ofpbuf_new (ofpbuf.c:151)
>     by 0x53BDE3: dpif_netlink_ct_get_limits (dpif-netlink.c:3025)
>     by 0x588B57: dpctl_ct_get_limits (dpctl.c:2178)
>     by 0x586FF2: dpctl_unixctl_handler (dpctl.c:2870)
>     by 0x52C241: process_command (unixctl.c:310)
>     by 0x52C241: run_connection (unixctl.c:344)
>     by 0x52C241: unixctl_server_run (unixctl.c:395)
>     by 0x407526: main (ovs-vswitchd.c:128)
>   Uninitialised value was created by a stack allocation
>     at 0x46AAA0: ct_dpif_get_limits (ct-dpif.c:197)
> 
> Fix that by using designated initializers that will clear all the
> non-specified fields.
> 
> CC: Yi-Hung Wei <yihung.wei at gmail.com>
> Fixes: 906ff9d229ee ("dpif-netlink: Implement conntrack zone limit")
> Signed-off-by: Ilya Maximets <i.maximets at ovn.org>
> ---
>  lib/dpif-netlink.c | 24 ++++++++++++++----------
>  1 file changed, 14 insertions(+), 10 deletions(-)
> 
> diff --git a/lib/dpif-netlink.c b/lib/dpif-netlink.c
> index ceb56c685..ee96f4011 100644
> --- a/lib/dpif-netlink.c
> +++ b/lib/dpif-netlink.c
> @@ -2923,8 +2923,6 @@ dpif_netlink_ct_set_limits(struct dpif *dpif OVS_UNUSED,
>                             const uint32_t *default_limits,
>                             const struct ovs_list *zone_limits)
>  {
> -    struct ovs_zone_limit req_zone_limit;
> -
>      if (ovs_ct_limit_family < 0) {
>          return EOPNOTSUPP;
>      }
> @@ -2941,8 +2939,10 @@ dpif_netlink_ct_set_limits(struct dpif *dpif OVS_UNUSED,
>      size_t opt_offset;
>      opt_offset = nl_msg_start_nested(request, OVS_CT_LIMIT_ATTR_ZONE_LIMIT);
>      if (default_limits) {
> -        req_zone_limit.zone_id = OVS_ZONE_LIMIT_DEFAULT_ZONE;
> -        req_zone_limit.limit = *default_limits;
> +        struct ovs_zone_limit req_zone_limit = {
> +            .zone_id = OVS_ZONE_LIMIT_DEFAULT_ZONE,
> +            .limit   = *default_limits,
> +        };
>          nl_msg_put(request, &req_zone_limit, sizeof req_zone_limit);
>      }
>  
> @@ -2950,8 +2950,10 @@ dpif_netlink_ct_set_limits(struct dpif *dpif OVS_UNUSED,
>          struct ct_dpif_zone_limit *zone_limit;
>  
>          LIST_FOR_EACH (zone_limit, node, zone_limits) {
> -            req_zone_limit.zone_id = zone_limit->zone;
> -            req_zone_limit.limit = zone_limit->limit;
> +            struct ovs_zone_limit req_zone_limit = {
> +                .zone_id = zone_limit->zone,
> +                .limit   = zone_limit->limit,
> +            };
>              nl_msg_put(request, &req_zone_limit, sizeof req_zone_limit);
>          }
>      }
> @@ -3035,8 +3037,9 @@ dpif_netlink_ct_get_limits(struct dpif *dpif OVS_UNUSED,
>          size_t opt_offset = nl_msg_start_nested(request,
>                                                  OVS_CT_LIMIT_ATTR_ZONE_LIMIT);
>  
> -        struct ovs_zone_limit req_zone_limit;
> -        req_zone_limit.zone_id = OVS_ZONE_LIMIT_DEFAULT_ZONE;
> +        struct ovs_zone_limit req_zone_limit = {
> +            .zone_id = OVS_ZONE_LIMIT_DEFAULT_ZONE,
> +        };
>          nl_msg_put(request, &req_zone_limit, sizeof req_zone_limit);
>  
>          struct ct_dpif_zone_limit *zone_limit;
> @@ -3086,8 +3089,9 @@ dpif_netlink_ct_del_limits(struct dpif *dpif OVS_UNUSED,
>  
>          struct ct_dpif_zone_limit *zone_limit;
>          LIST_FOR_EACH (zone_limit, node, zone_limits) {
> -            struct ovs_zone_limit req_zone_limit;
> -            req_zone_limit.zone_id = zone_limit->zone;
> +            struct ovs_zone_limit req_zone_limit = {
> +                .zone_id = zone_limit->zone,

Does this set 'limit' and 'count' automatically to 0? Is this behaviour
specified by the relevant c standard or is it compiler dependent?

> +            };
>              nl_msg_put(request, &req_zone_limit, sizeof req_zone_limit);
>          }
>          nl_msg_end_nested(request, opt_offset);
>