Medium [CVE-2026-64177] disable BH around forwarded sk_receive_skb

In the Linux kernel, the following vulnerability has been resolved: phonet/pep: disable BH around forwarded sk_receive_skb() The networking receive path is usually run from softirq context, but protocols that take the socket lock may have packets stored in the backlog and processed later from process context.

In that case release_sock() -> __release_sock() drops the slock with spin_unlock_bh() and then calls sk->sk_backlog_rcv() with bottom halves enabled.

Typical sk_backlog_rcv handlers process the socket whose backlog is being drained, so the BH state at entry is irrelevant for the slocks they touch. pep_do_rcv() is different: when the inbound skb targets an existing PEP pipe, it forwards the skb to a different *child* socket via sk_receive_skb().

That helper takes the child slock with bh_lock_sock_nested(), which is just spin_lock_nested() and assumes BH is already off. Discovered via in-house syzkaller fuzzing; the same root cause also on the linux-6.1.y syzbot dashboard as extid 44f0626dd6284f02663c.

Reproduced under KASAN + LOCKDEP + PROVE_LOCKING, reproducer: A flaw was found in the Linux kernel's Phonet Pipe End Point (PEP) protocol. This vulnerability arises from an inconsistent lock state when the pep_do_rcv() function forwards a packet to a child socket.

Affected products named by the advisory: Red Hat Enterprise Linux 6; Red Hat package: kernel.