ipv6: sr: enforce exact attribute length for SEG6_ATTR_DST

Overview

In the Linux kernel, the following vulnerability has been resolved:

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.

Affected

• Linux >= 915d7e5e5930b4f01d0971d93b9b25ed17d221aa < 050a0aa3c80907b8c60a396b7e04d48d8b1a9e70
• Linux >= 915d7e5e5930b4f01d0971d93b9b25ed17d221aa < 209eefebee54c4a5f01d68b61e8ac9881eca2de9
• Linux >= 915d7e5e5930b4f01d0971d93b9b25ed17d221aa < e3ac68c1cdc2535d127b2bfd50c263d16c8e4199
• Linux >= 915d7e5e5930b4f01d0971d93b9b25ed17d221aa < 66bf65fa109326e4c4ddeb0b94093379f72838fd
• Linux >= 915d7e5e5930b4f01d0971d93b9b25ed17d221aa < 195813bb7324c338eaba0aaa02b18681ee65b670
• Linux >= 915d7e5e5930b4f01d0971d93b9b25ed17d221aa < 6fcfc362344edea745a69f3a705de50b731f3418
• Linux >= 915d7e5e5930b4f01d0971d93b9b25ed17d221aa < 94214cf0a08dd2c5f37aeeea46078d9dfe8e4a0e
• Linux >= 915d7e5e5930b4f01d0971d93b9b25ed17d221aa < 2d959c75c27f90e9ec489d18ce5ee6b852ad4741
• Linux 4.10

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.