Wind River Support Network

Description

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. The same child slock therefore ends up acquired with BH on (process path) and with BH off (softirq path):    process context                   softirq context   ---------------                   ---------------   release_sock(listener)            __netif_receive_skb()    __release_sock()                  phonet_rcv()     spin_unlock_bh()                  __sk_receive_skb(listener)     [BH now ENABLED]                  [BH already disabled]     sk_backlog_rcv:                   sk_backlog_rcv:      pep_do_rcv()                      pep_do_rcv()       sk_receive_skb(child)             sk_receive_skb(child)        bh_lock_sock_nested(child)        bh_lock_sock_nested(child)        => SOFTIRQ-ON-W                   => IN-SOFTIRQ-W  Lockdep flags this as inconsistent lock state, and it can become a real self-deadlock if a softirq on the same CPU tries to receive to the same child socket while its slock is held in the BH-enabled path:    WARNING: inconsistent lock state   inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.    (slock-AF_PHONET/1){+.?.}-{3:3}, at: __sk_receive_skb+0x1cf/0x900     __sk_receive_skb              net/core/sock.c:563     sk_receive_skb                include/net/sock.h:2022 [inline]     pep_do_rcv                    net/phonet/pep.c:675     sk_backlog_rcv                include/net/sock.h:1190     __release_sock                net/core/sock.c:3216     release_sock                  net/core/sock.c:3815     pep_sock_accept               net/phonet/pep.c:879  Wrap the forwarded sk_receive_skb() in local_bh_disable() / local_bh_enable() so the child slock is always acquired with BH off. local_bh_disable() nests safely on the softirq path.  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: https://pastebin.com/A3t8xzCR