On Wed, Dec 22, 2021 at 5:40 PM Jakub Kicinski <kuba@xxxxxxxxxx> wrote: > > On Tue, 21 Dec 2021 14:51:52 -0500 Xin Long wrote: > > This patch is to delay the endpoint free by calling call_rcu() to fix > > another use-after-free issue in sctp_sock_dump(): > > > > BUG: KASAN: use-after-free in __lock_acquire+0x36d9/0x4c20 > > Call Trace: > > __lock_acquire+0x36d9/0x4c20 kernel/locking/lockdep.c:3218 > > lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3844 > > __raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline] > > _raw_spin_lock_bh+0x31/0x40 kernel/locking/spinlock.c:168 > > spin_lock_bh include/linux/spinlock.h:334 [inline] > > __lock_sock+0x203/0x350 net/core/sock.c:2253 > > lock_sock_nested+0xfe/0x120 net/core/sock.c:2774 > > lock_sock include/net/sock.h:1492 [inline] > > sctp_sock_dump+0x122/0xb20 net/sctp/diag.c:324 > > sctp_for_each_transport+0x2b5/0x370 net/sctp/socket.c:5091 > > sctp_diag_dump+0x3ac/0x660 net/sctp/diag.c:527 > > __inet_diag_dump+0xa8/0x140 net/ipv4/inet_diag.c:1049 > > inet_diag_dump+0x9b/0x110 net/ipv4/inet_diag.c:1065 > > netlink_dump+0x606/0x1080 net/netlink/af_netlink.c:2244 > > __netlink_dump_start+0x59a/0x7c0 net/netlink/af_netlink.c:2352 > > netlink_dump_start include/linux/netlink.h:216 [inline] > > inet_diag_handler_cmd+0x2ce/0x3f0 net/ipv4/inet_diag.c:1170 > > __sock_diag_cmd net/core/sock_diag.c:232 [inline] > > sock_diag_rcv_msg+0x31d/0x410 net/core/sock_diag.c:263 > > netlink_rcv_skb+0x172/0x440 net/netlink/af_netlink.c:2477 > > sock_diag_rcv+0x2a/0x40 net/core/sock_diag.c:274 > > > > This issue occurs when asoc is peeled off and the old sk is freed after > > getting sk by asoc->base.sk and before calling lock_sock(sk). > > > > To prevent the ep/sk free, this patch is to call call_rcu to free the ep > > and hold it under rcu_read_lock to make sure that sk in sctp_sock_dump > > is still alive when calling lock_sock(). > > Could you clarify a little more where the RCU lock is held, it's not > obvious. sure, will do. > > > Note that delaying endpint free won't delay the port release, as the port > > release happens in sctp_endpoint_destroy() before calling call_rcu(). > > Also, freeing endpoint by call_rcu() makes it safe to access the sk by > > asoc->base.sk in sctp_assocs_seq_show() and sctp_rcv(). > > > > Thanks Jones to bring this issue up. > > > > Reported-by: syzbot+9276d76e83e3bcde6c99@xxxxxxxxxxxxxxxxxxxxxxxxx > > Reported-by: Lee Jones <lee.jones@xxxxxxxxxx> > > Fixes: d25adbeb0cdb ("sctp: fix an use-after-free issue in sctp_sock_dump") > > Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx> > > > diff --git a/net/sctp/endpointola.c b/net/sctp/endpointola.c > > index 48c9c2c7602f..81fb97d382d7 100644 > > --- a/net/sctp/endpointola.c > > +++ b/net/sctp/endpointola.c > > @@ -184,6 +184,17 @@ void sctp_endpoint_free(struct sctp_endpoint *ep) > > } > > > > /* Final destructor for endpoint. */ > > +static void sctp_endpoint_destroy_rcu(struct rcu_head *head) > > +{ > > + struct sctp_endpoint *ep = container_of(head, struct sctp_endpoint, rcu); > > + struct sock *sk = ep->base.sk; > > + > > + sctp_sk(sk)->ep = NULL; > > + sock_put(sk); > > + > > + SCTP_DBG_OBJCNT_DEC(ep); > > +} > > + > > static void sctp_endpoint_destroy(struct sctp_endpoint *ep) > > { > > struct sock *sk; > > @@ -213,18 +224,13 @@ static void sctp_endpoint_destroy(struct sctp_endpoint *ep) > > if (sctp_sk(sk)->bind_hash) > > sctp_put_port(sk); > > > > - sctp_sk(sk)->ep = NULL; > > - /* Give up our hold on the sock */ > > - sock_put(sk); > > - > > - kfree(ep); > > where does this kfree() go after the change? Good catch, somehow I didn't move it into sctp_endpoint_destroy_rcu(). will post v2. Thanks! > > > - SCTP_DBG_OBJCNT_DEC(ep); > > + call_rcu(&ep->rcu, sctp_endpoint_destroy_rcu); > > }