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: Tue, 14 Nov 2017 20:52:56 +0800 Message-ID: References: <20171113144653.GA7876@hmswarspite.think-freely.org> <20171114124328.GA21954@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-f194.google.com ([209.85.220.194]:47860 "EHLO mail-qk0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753971AbdKNMw5 (ORCPT ); Tue, 14 Nov 2017 07:52:57 -0500 In-Reply-To: <20171114124328.GA21954@hmswarspite.think-freely.org> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, Nov 14, 2017 at 8:43 PM, Neil Horman wrote: > On Mon, Nov 13, 2017 at 11:29:49PM +0800, Xin Long wrote: >> 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; >> > That would work, but it also seems just as easy to check in sctp_sendmsg. that > is to say, if sctp_wait_for_sndbuf return -EPIPE sctp_sndmsg jumps to out_free, > where we can check to see if (new_assoc && new_assoc->base.dead) as a gating > factor on free. we can't do that, as nowhere holds new_assoc, it may be already destroyed. to dereference it (new_assoc->base.dead) will cause use-after-free panic. I may do like this: err = sctp_wait_for_sndbuf(asoc, &timeo, msg_len); - if (err) + if (err) { + if (err == -ESRCH) { + /* asoc is already dead; */ + new_asoc = NULL; + err = -EPIPE; + } goto out_free; + } agree ? > > Neil >> > >> > Neil >> > >> From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xin Long Date: Tue, 14 Nov 2017 12:52:56 +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> <20171114124328.GA21954@hmswarspite.think-freely.org> In-Reply-To: <20171114124328.GA21954@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 Tue, Nov 14, 2017 at 8:43 PM, Neil Horman wrote: > On Mon, Nov 13, 2017 at 11:29:49PM +0800, Xin Long wrote: >> 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; >> > That would work, but it also seems just as easy to check in sctp_sendmsg. that > is to say, if sctp_wait_for_sndbuf return -EPIPE sctp_sndmsg jumps to out_free, > where we can check to see if (new_assoc && new_assoc->base.dead) as a gating > factor on free. we can't do that, as nowhere holds new_assoc, it may be already destroyed. to dereference it (new_assoc->base.dead) will cause use-after-free panic. I may do like this: err = sctp_wait_for_sndbuf(asoc, &timeo, msg_len); - if (err) + if (err) { + if (err = -ESRCH) { + /* asoc is already dead; */ + new_asoc = NULL; + err = -EPIPE; + } goto out_free; + } agree ? > > Neil >> > >> > Neil >> > >>