From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xin Long Subject: Re: [PATCH net] sctp: do not free asoc when it is already dead in sctp_sendmsg Date: Mon, 13 Nov 2017 23:29:49 +0800 Message-ID: References: <20171113144653.GA7876@hmswarspite.think-freely.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: network dev , linux-sctp@vger.kernel.org, davem , Marcelo Ricardo Leitner , Dmitry Vyukov , syzkaller To: Neil Horman Return-path: Received: from mail-qk0-f196.google.com ([209.85.220.196]:57060 "EHLO mail-qk0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752513AbdKMP3v (ORCPT ); Mon, 13 Nov 2017 10:29:51 -0500 In-Reply-To: <20171113144653.GA7876@hmswarspite.think-freely.org> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, Nov 13, 2017 at 10:46 PM, Neil Horman wrote: > On Mon, Nov 13, 2017 at 12:43:50PM +0800, Xin Long wrote: >> Now in sctp_sendmsg sctp_wait_for_sndbuf could schedule out without >> holding sock sk. It means the current asoc can be freed elsewhere, >> like when receiving an abort packet. >> >> If the asoc is just created in sctp_sendmsg and sctp_wait_for_sndbuf >> returns err, the asoc will be freed again due to new_asoc is not nil. >> An use-after-free issue would be triggered by this. >> >> This patch is to fix it by setting new_asoc with nil if the asoc is >> already dead when cpu schedules back, so that it will not be freed >> again in sctp_sendmsg. >> >> Reported-by: Dmitry Vyukov >> Signed-off-by: Xin Long >> --- >> net/sctp/socket.c | 15 +++++++++------ >> 1 file changed, 9 insertions(+), 6 deletions(-) >> >> diff --git a/net/sctp/socket.c b/net/sctp/socket.c >> index 6f45d17..f575976 100644 >> --- a/net/sctp/socket.c >> +++ b/net/sctp/socket.c >> @@ -83,8 +83,8 @@ >> /* Forward declarations for internal helper functions. */ >> static int sctp_writeable(struct sock *sk); >> static void sctp_wfree(struct sk_buff *skb); >> -static int sctp_wait_for_sndbuf(struct sctp_association *, long *timeo_p, >> - size_t msg_len); >> +static int sctp_wait_for_sndbuf(struct sctp_association *asoc, long *timeo_p, >> + size_t msg_len, struct sctp_association **new); >> static int sctp_wait_for_packet(struct sock *sk, int *err, long *timeo_p); >> static int sctp_wait_for_connect(struct sctp_association *, long *timeo_p); >> static int sctp_wait_for_accept(struct sock *sk, long timeo); >> @@ -1962,7 +1962,7 @@ static int sctp_sendmsg(struct sock *sk, struct msghdr *msg, size_t msg_len) >> >> timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT); >> if (!sctp_wspace(asoc)) { >> - err = sctp_wait_for_sndbuf(asoc, &timeo, msg_len); >> + err = sctp_wait_for_sndbuf(asoc, &timeo, msg_len, &new_asoc); >> if (err) >> goto out_free; >> } >> @@ -7822,7 +7822,7 @@ void sctp_sock_rfree(struct sk_buff *skb) >> >> /* Helper function to wait for space in the sndbuf. */ >> static int sctp_wait_for_sndbuf(struct sctp_association *asoc, long *timeo_p, >> - size_t msg_len) >> + size_t msg_len, struct sctp_association **new) >> { >> struct sock *sk = asoc->base.sk; >> int err = 0; >> @@ -7839,10 +7839,13 @@ static int sctp_wait_for_sndbuf(struct sctp_association *asoc, long *timeo_p, >> for (;;) { >> prepare_to_wait_exclusive(&asoc->wait, &wait, >> TASK_INTERRUPTIBLE); >> + if (asoc->base.dead) { >> + *new = NULL; >> + goto do_error; >> + } >> if (!*timeo_p) >> goto do_nonblock; >> - if (sk->sk_err || asoc->state >= SCTP_STATE_SHUTDOWN_PENDING || >> - asoc->base.dead) >> + if (sk->sk_err || asoc->state >= SCTP_STATE_SHUTDOWN_PENDING) >> goto do_error; >> if (signal_pending(current)) >> goto do_interrupted; >> -- >> 2.1.0 >> >> > Why pass a pointer to a pointer into the wait function? It seems like you could > just check the return code for err == -EPIPE and set the association to null in > sctp_sendmsg. That would avoid passing another parameter, and cut down on some > complexity here. "if (sk->sk_err || asoc->state >= SCTP_STATE_SHUTDOWN_PENDING)" also goes to err == -EPIPE path, with it, the new_asoc are supposed to be freed in old codes. do you think it's good to not free it now when sk->sk_err or SHUTDOWN_PENDING ? or I can add another err path like: +do_dead: + err = -ESRCH; + goto out; > > Neil > From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xin Long Date: Mon, 13 Nov 2017 15:29:49 +0000 Subject: Re: [PATCH net] sctp: do not free asoc when it is already dead in sctp_sendmsg Message-Id: List-Id: References: <20171113144653.GA7876@hmswarspite.think-freely.org> In-Reply-To: <20171113144653.GA7876@hmswarspite.think-freely.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Neil Horman Cc: network dev , linux-sctp@vger.kernel.org, davem , Marcelo Ricardo Leitner , Dmitry Vyukov , syzkaller On Mon, Nov 13, 2017 at 10:46 PM, Neil Horman wrote: > On Mon, Nov 13, 2017 at 12:43:50PM +0800, Xin Long wrote: >> Now in sctp_sendmsg sctp_wait_for_sndbuf could schedule out without >> holding sock sk. It means the current asoc can be freed elsewhere, >> like when receiving an abort packet. >> >> If the asoc is just created in sctp_sendmsg and sctp_wait_for_sndbuf >> returns err, the asoc will be freed again due to new_asoc is not nil. >> An use-after-free issue would be triggered by this. >> >> This patch is to fix it by setting new_asoc with nil if the asoc is >> already dead when cpu schedules back, so that it will not be freed >> again in sctp_sendmsg. >> >> Reported-by: Dmitry Vyukov >> Signed-off-by: Xin Long >> --- >> net/sctp/socket.c | 15 +++++++++------ >> 1 file changed, 9 insertions(+), 6 deletions(-) >> >> diff --git a/net/sctp/socket.c b/net/sctp/socket.c >> index 6f45d17..f575976 100644 >> --- a/net/sctp/socket.c >> +++ b/net/sctp/socket.c >> @@ -83,8 +83,8 @@ >> /* Forward declarations for internal helper functions. */ >> static int sctp_writeable(struct sock *sk); >> static void sctp_wfree(struct sk_buff *skb); >> -static int sctp_wait_for_sndbuf(struct sctp_association *, long *timeo_p, >> - size_t msg_len); >> +static int sctp_wait_for_sndbuf(struct sctp_association *asoc, long *timeo_p, >> + size_t msg_len, struct sctp_association **new); >> static int sctp_wait_for_packet(struct sock *sk, int *err, long *timeo_p); >> static int sctp_wait_for_connect(struct sctp_association *, long *timeo_p); >> static int sctp_wait_for_accept(struct sock *sk, long timeo); >> @@ -1962,7 +1962,7 @@ static int sctp_sendmsg(struct sock *sk, struct msghdr *msg, size_t msg_len) >> >> timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT); >> if (!sctp_wspace(asoc)) { >> - err = sctp_wait_for_sndbuf(asoc, &timeo, msg_len); >> + err = sctp_wait_for_sndbuf(asoc, &timeo, msg_len, &new_asoc); >> if (err) >> goto out_free; >> } >> @@ -7822,7 +7822,7 @@ void sctp_sock_rfree(struct sk_buff *skb) >> >> /* Helper function to wait for space in the sndbuf. */ >> static int sctp_wait_for_sndbuf(struct sctp_association *asoc, long *timeo_p, >> - size_t msg_len) >> + size_t msg_len, struct sctp_association **new) >> { >> struct sock *sk = asoc->base.sk; >> int err = 0; >> @@ -7839,10 +7839,13 @@ static int sctp_wait_for_sndbuf(struct sctp_association *asoc, long *timeo_p, >> for (;;) { >> prepare_to_wait_exclusive(&asoc->wait, &wait, >> TASK_INTERRUPTIBLE); >> + if (asoc->base.dead) { >> + *new = NULL; >> + goto do_error; >> + } >> if (!*timeo_p) >> goto do_nonblock; >> - if (sk->sk_err || asoc->state >= SCTP_STATE_SHUTDOWN_PENDING || >> - asoc->base.dead) >> + if (sk->sk_err || asoc->state >= SCTP_STATE_SHUTDOWN_PENDING) >> goto do_error; >> if (signal_pending(current)) >> goto do_interrupted; >> -- >> 2.1.0 >> >> > Why pass a pointer to a pointer into the wait function? It seems like you could > just check the return code for err = -EPIPE and set the association to null in > sctp_sendmsg. That would avoid passing another parameter, and cut down on some > complexity here. "if (sk->sk_err || asoc->state >= SCTP_STATE_SHUTDOWN_PENDING)" also goes to err = -EPIPE path, with it, the new_asoc are supposed to be freed in old codes. do you think it's good to not free it now when sk->sk_err or SHUTDOWN_PENDING ? or I can add another err path like: +do_dead: + err = -ESRCH; + goto out; > > Neil >