net: Fix routing tables with id > 255 for legacy software

Most legacy software do not like tables > 255 as rtm_table is u8
so tb_id is sent &0xff and it is possible to mismatch for example
table 510 with table 254 (main).

This patch introduces RT_TABLE_COMPAT=252 so the code uses it if
tb_id > 255. It makes such old applications happy, new
ones are still able to use RTA_TABLE to get a proper table id.

Signed-off-by: Krzysztof Piotr Oledzki <ole@ans.pl>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 5 insertions, 1 deletions

diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index a2aec2c0cfb5..b358c704d102 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -246,6 +246,7 @@ enum rt_class_t
 {
         RT_TABLE_UNSPEC=0,
 /* User defined values */
+        RT_TABLE_COMPAT=252,
         RT_TABLE_DEFAULT=253,
         RT_TABLE_MAIN=254,
         RT_TABLE_LOCAL=255,
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 3b83c34019fc..0d4d72827e4b 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -960,7 +960,10 @@ int fib_dump_info(struct sk_buff *skb, u32 pid, u32 seq, int event,
         rtm->rtm_dst_len = dst_len;
         rtm->rtm_src_len = 0;
         rtm->rtm_tos = tos;
-        rtm->rtm_table = tb_id;
+        if (tb_id < 256)
+                rtm->rtm_table = tb_id;
+        else
+                rtm->rtm_table = RT_TABLE_COMPAT;
         NLA_PUT_U32(skb, RTA_TABLE, tb_id);
         rtm->rtm_type = type;
         rtm->rtm_flags = fi->fib_flags;