CVE-2026-43198

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

tcp: fix potential race in tcp_v6_syn_recv_sock()

Code in tcp_v6_syn_recv_sock() after the call to tcp_v4_syn_recv_sock()

is done too late.

After tcp_v4_syn_recv_sock(), the child socket is already visible

from TCP ehash table and other cpus might use it.

Since newinet->pinet6 is still pointing to the listener ipv6_pinfo

bad things can happen as syzbot found.

Move the problematic code in tcp_v6_mapped_child_init()

and call this new helper from tcp_v4_syn_recv_sock() before

the ehash insertion.

This allows the removal of one tcp_sync_mss(), since

tcp_v4_syn_recv_sock() will call it with the correct

context.