ipv6: do not let ipv6_find_hdr() return an offset past the packet end

Overview

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

ipv6: do not let ipv6_find_hdr() return an offset past the packet end

ipv6_find_hdr() walks the extension header chain, skipping each header by the length that header itself declares. ipv6_optlen() returns up to 2048, and the skip is never checked against skb->len, so the offset stored in *offset can point past the end of the packet.

openvswitch installs that offset as the transport header, and update_ipv6_checksum() then reads and writes the transport checksum field out of bounds:

BUG: KASAN: slab-use-after-free in inet_proto_csum_replace16+0x445/0x470 Read of size 2 at addr ffff88810b754b06 by task ovs_ipv6_oob/629 CPU: 4 UID: 1000 PID: 629 Comm: ovs_ipv6_oob Tainted: G N 7.3.0-rc3+ #348 Call Trace: inet_proto_csum_replace16+0x445/0x470 set_ipv6_addr+0x3dd/0x460 do_execute_actions+0x6a3d/0x7c40 ovs_execute_actions+0xfd/0x480 ovs_packet_cmd_execute+0xc38/0xf20 genl_rcv_msg+0x59e/0x870 netlink_rcv_skb+0x18b/0x450 genl_rcv+0x2d/0x40 netlink_unicast+0x6bc/0xa20

The buggy address belongs to the object at ffff88810b754980 which belongs to the cache skbuff_small_head of size 704 The buggy address is located 390 bytes inside of freed 704-byte region [ffff88810b754980, ffff88810b754c40)

Other callers use that offset too, so bound it here rather than in one caller.

Reject a header whose declared length does not fit in the packet. ipv6_find_hdr() already fails with -EBADMSG on a malformed chain, so this adds no new failure mode.

Affected

• Linux >= f8f626754ebeca613cf1af2e6f890cfde0e74d5b < ca96b38730e31357ef4a9d76af1336958ac670d7
• Linux >= f8f626754ebeca613cf1af2e6f890cfde0e74d5b < 531255de8971c06d5d5986f85fdc2525d707ba71
• Linux >= f8f626754ebeca613cf1af2e6f890cfde0e74d5b < 543354c6efb27eae3372a3a9674aeaa2a86e2b2c
• Linux >= f8f626754ebeca613cf1af2e6f890cfde0e74d5b < dc92cb972e86790b8078337ec41015b748b8f8e5
• Linux >= f8f626754ebeca613cf1af2e6f890cfde0e74d5b < 1c70275ca87e769e1a52abc644d61372d8c016cb
• Linux >= f8f626754ebeca613cf1af2e6f890cfde0e74d5b < 1d42828565889632068fbc2983c34d57c66af4e0
• Linux >= f8f626754ebeca613cf1af2e6f890cfde0e74d5b < 4254d5878c320c19961dd0b8e1d0aca4800d8b7d
• Linux >= f8f626754ebeca613cf1af2e6f890cfde0e74d5b < ee319bd3a0e976af5087cbe59ebc50a66f31d202
• Linux 3.8

Remediation

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