From 2d959c75c27f90e9ec489d18ce5ee6b852ad4741 Mon Sep 17 00:00:00 2001 From: Hui Peng Date: Mon, 21 Sep 2026 04:40:25 +0000 Subject: [PATCH] ipv6: sr: enforce exact attribute length for SEG6_ATTR_DST In seg6_genl_policy, SEG6_ATTR_DST is defined with .type = NLA_BINARY and .len = sizeof(struct in6_addr). For NLA_BINARY, .len only enforces the maximum payload length and permits shorter payloads (e.g., 0 bytes). When seg6_genl_set_tunsrc() copies sizeof(struct in6_addr) bytes via kmemdup(val, sizeof(*val), GFP_KERNEL), a short SEG6_ATTR_DST attribute triggers a 16-byte out-of-bounds read past skb->tail into uninitialized skb->head memory, which is stored in sdata->tun_src and leaked back to userspace via SEG6_CMD_GET_TUNSRC. Switch SEG6_ATTR_DST in seg6_genl_policy to NLA_POLICY_EXACT_LEN(sizeof(struct in6_addr)) so that generic netlink validation rejects any attribute whose length is not exactly sizeof(struct in6_addr) with -ERANGE. Tested in QEMU against Linux 7.3.0-rc3 by sending a SEG6_CMD_SET_TUNSRC Generic Netlink message with a 0-byte SEG6_ATTR_DST attribute followed by SEG6_CMD_GET_TUNSRC. On the unfixed kernel, SEG6_CMD_SET_TUNSRC succeeds (err = 0) and SEG6_CMD_GET_TUNSRC leaks 16 bytes of uninitialized kernel heap memory (tun_src = 836a61ecc4d25a1042a8d60411cfb378); with this patch applied, SEG6_CMD_SET_TUNSRC is rejected by netlink policy validation with -ERANGE (-34) and tun_src remains zeroed. Fixes: 915d7e5e5930 ("ipv6: sr: add code base for control plane support of SR-IPv6") Cc: stable@vger.kernel.org Signed-off-by: Hui Peng Reviewed-by: Hangbin Liu Reviewed-by: Justin Iurman Reviewed-by: Andrea Mayer Link: https://patch.msgid.link/20260921044025.1535982-1-benquike@gmail.com Signed-off-by: Jakub Kicinski --- net/ipv6/seg6.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/ipv6/seg6.c b/net/ipv6/seg6.c index 62a7eb779202..8c2b156c227a 100644 --- a/net/ipv6/seg6.c +++ b/net/ipv6/seg6.c @@ -138,8 +138,8 @@ void seg6_icmp_srh(struct sk_buff *skb, struct inet6_skb_parm *opt) static struct genl_family seg6_genl_family; static const struct nla_policy seg6_genl_policy[SEG6_ATTR_MAX + 1] = { - [SEG6_ATTR_DST] = { .type = NLA_BINARY, - .len = sizeof(struct in6_addr) }, + [SEG6_ATTR_DST] = + NLA_POLICY_EXACT_LEN(sizeof(struct in6_addr)), [SEG6_ATTR_DSTLEN] = { .type = NLA_S32, }, [SEG6_ATTR_HMACKEYID] = { .type = NLA_U32, }, [SEG6_ATTR_SECRET] = { .type = NLA_BINARY, },