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ipv6: sr: enforce exact attribute length for SEG6_ATTR_DST

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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: 915d7e5e59 ("ipv6: sr: add code base for control plane support of SR-IPv6")
Cc: stable@vger.kernel.org
Signed-off-by: Hui Peng <benquike@gmail.com>
Reviewed-by: Hangbin Liu <liuhangbin@kylinos.cn>
Reviewed-by: Justin Iurman <justin.iurman@gmail.com>
Reviewed-by: Andrea Mayer <andrea.mayer@uniroma2.it>
Link: https://patch.msgid.link/20260921044025.1535982-1-benquike@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Hui Peng 2026-09-21 04:40:25 +00:00 committed by Jakub Kicinski
parent ab7aa05c06
commit 2d959c75c2
1 changed files with 2 additions and 2 deletions
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4
net/ipv6/seg6.c
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@ -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, },