io_uring/net: populate CONNECT filter fields for 24-byte sockaddr_in6

Overview

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

io_uring/net: populate CONNECT filter fields for 24-byte sockaddr_in6

io_connect_bpf_populate() fills connect.port and connect.v6_addr for AF_INET6 only when addr_len >= sizeof(struct sockaddr_in6), i.e. 28 bytes.

The IPv6 connect paths accept SIN6_LEN_RFC2133 (24 bytes), which already holds sin6_port and sin6_addr. io_connect() passes addr_len to the socket layer unchanged.

At addr_len 24 the filter sees family AF_INET6 with port and address zero, while the kernel connects to the real destination. A filter that denies an IPv6 port or address is bypassed. Denying connect.port == P rejects [::1]:P with -EACCES at addr_len 28 but connects at addr_len 24.

Use SIN6_LEN_RFC2133 as the threshold. sin6_scope_id stays zero when absent.

The threshold mismatch was found by an AI coding assistant (Claude Code) comparing this hook against the net/ipv6 length checks on my instructions; it also drafted the reproducer and this patch. I verified the bypass and the fix in a VM on 7.3-rc6 and that 7.2 has the same code.

Affected

• Linux >= 899bea8248cee35d54760a5e7d61a76af8e64411 < 596a955d2d01b7e29d9fed60ebcf7c4ba518b8e5
• Linux >= 899bea8248cee35d54760a5e7d61a76af8e64411 < aa5d5f8e502318e783545ba5d04bb40130b83e20
• Linux 7.2

Remediation

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