The struct ip_tunnel_info has a flexible array member named options that is protected by a counted_by(options_len) attribute.

The compiler will use this information to enforce runtime bounds checking deployed by FORTIFY_SOURCE string helpers.

As laid out in the GCC documentation, the counter must be initialized before the first reference to the flexible array member.

In the normal case the ip_tunnel_info_opts_set() helper is used which would initialize options_len properly, however in the GRE ERSPAN code a partial update is done, preventing the use of the helper function.

Before this change the handling of ERSPAN traffic in GRE tunnels would cause a kernel panic when the kernel is compiled with GCC 15+ and having FORTIFY_SOURCE configured:

memcpy: detected buffer overflow: 4 byte write of buffer size 0

Call Trace: <IRQ> __fortify_panic+0xd/0xf erspan_rcv.cold+0x68/0x83 ? ip_route_input_slow+0x816/0x9d0 gre_rcv+0x1b2/0x1c0 gre_rcv+0x8e/0x100 ? raw_v4_input+0x2a0/0x2b0 ip_protocol_deliver_rcu+0x1ea/0x210 ip_local_deliver_finish+0x86/0x110 ip_local_deliver+0x65/0x110 ? ip_rcv_finish_core+0xd6/0x360 ip_rcv+0x186/0x1a0

Link: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-cou... Reported-at: https://launchpad.net/bugs/2129580 Fixes: bb5e62f2d547 ("net: Add options as a flexible array to struct ip_tunnel_info") Signed-off-by: Frode Nordahl fnordahl@ubuntu.com --- net/ipv4/ip_gre.c | 18 ++++++++++++++++-- net/ipv6/ip6_gre.c | 18 ++++++++++++++++-- 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c index 761a53c6a89a..285a656c9e41 100644 --- a/net/ipv4/ip_gre.c +++ b/net/ipv4/ip_gre.c @@ -330,6 +330,22 @@ static int erspan_rcv(struct sk_buff *skb, struct tnl_ptk_info *tpi, if (!tun_dst) return PACKET_REJECT;

+ /* The struct ip_tunnel_info has a flexible array member named + * options that is protected by a counted_by(options_len) + * attribute. + * + * The compiler will use this information to enforce runtime bounds + * checking deployed by FORTIFY_SOURCE string helpers. + * + * As laid out in the GCC documentation, the counter must be + * initialized before the first reference to the flexible array + * member. + * + * Link: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-cou... + */ + info = &tun_dst->u.tun_info; + info->options_len = sizeof(*md); + /* skb can be uncloned in __iptunnel_pull_header, so * old pkt_md is no longer valid and we need to reset * it @@ -344,10 +360,8 @@ static int erspan_rcv(struct sk_buff *skb, struct tnl_ptk_info *tpi, memcpy(md2, pkt_md, ver == 1 ? ERSPAN_V1_MDSIZE : ERSPAN_V2_MDSIZE);

- info = &tun_dst->u.tun_info; __set_bit(IP_TUNNEL_ERSPAN_OPT_BIT, info->key.tun_flags); - info->options_len = sizeof(*md); }

skb_reset_mac_header(skb); diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c index c82a75510c0e..eb840a11b93b 100644 --- a/net/ipv6/ip6_gre.c +++ b/net/ipv6/ip6_gre.c @@ -535,6 +535,22 @@ static int ip6erspan_rcv(struct sk_buff *skb, if (!tun_dst) return PACKET_REJECT;

+ /* The struct ip_tunnel_info has a flexible array member named + * options that is protected by a counted_by(options_len) + * attribute. + * + * The compiler will use this information to enforce runtime bounds + * checking deployed by FORTIFY_SOURCE string helpers. + * + * As laid out in the GCC documentation, the counter must be + * initialized before the first reference to the flexible array + * member. + * + * Link: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-cou... + */ + info = &tun_dst->u.tun_info; + info->options_len = sizeof(*md); + /* skb can be uncloned in __iptunnel_pull_header, so * old pkt_md is no longer valid and we need to reset * it @@ -543,7 +559,6 @@ static int ip6erspan_rcv(struct sk_buff *skb, skb_network_header_len(skb); pkt_md = (struct erspan_metadata *)(gh + gre_hdr_len + sizeof(*ershdr)); - info = &tun_dst->u.tun_info; md = ip_tunnel_info_opts(info); md->version = ver; md2 = &md->u.md2; @@ -551,7 +566,6 @@ static int ip6erspan_rcv(struct sk_buff *skb, ERSPAN_V2_MDSIZE); __set_bit(IP_TUNNEL_ERSPAN_OPT_BIT, info->key.tun_flags); - info->options_len = sizeof(*md);

ip6_tnl_rcv(tunnel, skb, tpi, tun_dst, log_ecn_error);