[PATCH net-next v10 04/10] ipv6: Set HBH and DestOpt limits to 2

Tom Herbert
2026-05-04T18:52:55Z

Set the default limits of non-padding Hop-by-Hop and Destination
options to 2. This means that if a packet contains more than two
non-padding options then it will be dropped. The previous limit
was 8, but that was too liberal considering that the stack only
support two Destination Options and the most Hop-by-Hop options
likely to ever be in the same packet are IOAM and JUMBO. The limit
can be increased via sysctl for private use and experimentation.

Signed-off-by: Tom Herbert <tom@herbertland.com>
Reviewed-by: Justin Iurman <justin.iurman@gmail.com>
---
include/net/ipv6.h | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index d042afe7a245..28448189d2e9 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -84,9 +84,12 @@ struct ip_tunnel_info;
* silently discarded.
*/

-/* Default limits for Hop-by-Hop and Destination options */
-#define IP6_DEFAULT_MAX_DST_OPTS_CNT 8
-#define IP6_DEFAULT_MAX_HBH_OPTS_CNT 8
+/* Default limits for Hop-by-Hop and Destination non-padding options. The
+ * default value for both is 2. This sets a limit at two non-padding options
+ * (see sysctl documentation)
+ */
+#define IP6_DEFAULT_MAX_DST_OPTS_CNT 2
+#define IP6_DEFAULT_MAX_HBH_OPTS_CNT 2
#define IP6_DEFAULT_MAX_DST_OPTS_LEN INT_MAX /* No limit */
#define IP6_DEFAULT_MAX_HBH_OPTS_LEN INT_MAX /* No limit */

--
2.43.0