[PATCH net] sctp: fix race on sctp_id2asoc

[PATCH net] sctp: fix race on sctp_id2asoc

[Marcelo Ricardo Leitner]

syzbot reported an use-after-free involving sctp_id2asoc.  Dmitry Vyukov
helped to root cause it and it is because of reading the asoc after it
was freed:

        CPU 1                       CPU 2
(working on socket 1)            (working on socket 2)
	                         sctp_association_destroy
sctp_id2asoc
   spin lock
     grab the asoc from idr
   spin unlock
                                   spin lock
				     remove asoc from idr
				   spin unlock
				   free(asoc)
   if asoc->base.sk != sk ... [*]

This can only be hit if trying to fetch asocs from different sockets. As
we have a single IDR for all asocs, in all SCTP sockets, their id is
unique on the system. An application can try to send stuff on an id
that matches on another socket, and the if in [*] will protect from such
usage. But it didn't consider that as that asoc may belong to another
socket, it may be freed in parallel (read: under another socket lock).

We fix it by moving the checks in [*] into the protected region. This
fixes it because the asoc cannot be freed while the lock is held.

Reported-by: syzbot+c7dd55d7aec49d48e49a@syzkaller.appspotmail.com
Acked-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
---
 net/sctp/socket.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index f73e9d38d5ba734d7ee3347e4015fd30d355bbfa..a7722f43aa69801c31409d4914c99946ee5533f5 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -271,11 +271,10 @@ struct sctp_association *sctp_id2assoc(struct sock *sk, sctp_assoc_t id)
 
 	spin_lock_bh(&sctp_assocs_id_lock);
 	asoc = (struct sctp_association *)idr_find(&sctp_assocs_id, (int)id);
+	if (asoc && (asoc->base.sk != sk || asoc->base.dead))
+		asoc = NULL;
 	spin_unlock_bh(&sctp_assocs_id_lock);
 
-	if (!asoc || (asoc->base.sk != sk) || asoc->base.dead)
-		return NULL;
-
 	return asoc;
 }
 
-- 
2.17.1

[PATCH net] sctp: fix race on sctp_id2asoc

[Marcelo Ricardo Leitner]

syzbot reported an use-after-free involving sctp_id2asoc.  Dmitry Vyukov
helped to root cause it and it is because of reading the asoc after it
was freed:

        CPU 1                       CPU 2
(working on socket 1)            (working on socket 2)
	                         sctp_association_destroy
sctp_id2asoc
   spin lock
     grab the asoc from idr
   spin unlock
                                   spin lock
				     remove asoc from idr
				   spin unlock
				   free(asoc)
   if asoc->base.sk != sk ... [*]

This can only be hit if trying to fetch asocs from different sockets. As
we have a single IDR for all asocs, in all SCTP sockets, their id is
unique on the system. An application can try to send stuff on an id
that matches on another socket, and the if in [*] will protect from such
usage. But it didn't consider that as that asoc may belong to another
socket, it may be freed in parallel (read: under another socket lock).

We fix it by moving the checks in [*] into the protected region. This
fixes it because the asoc cannot be freed while the lock is held.

Reported-by: syzbot+c7dd55d7aec49d48e49a@syzkaller.appspotmail.com
Acked-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
---
 net/sctp/socket.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index f73e9d38d5ba734d7ee3347e4015fd30d355bbfa..a7722f43aa69801c31409d4914c99946ee5533f5 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -271,11 +271,10 @@ struct sctp_association *sctp_id2assoc(struct sock *sk, sctp_assoc_t id)
 
 	spin_lock_bh(&sctp_assocs_id_lock);
 	asoc = (struct sctp_association *)idr_find(&sctp_assocs_id, (int)id);
+	if (asoc && (asoc->base.sk != sk || asoc->base.dead))
+		asoc = NULL;
 	spin_unlock_bh(&sctp_assocs_id_lock);
 
-	if (!asoc || (asoc->base.sk != sk) || asoc->base.dead)
-		return NULL;
-
 	return asoc;
 }
 
-- 
2.17.1

Re: [PATCH net] sctp: fix race on sctp_id2asoc

[Neil Horman]

On Tue, Oct 16, 2018 at 03:18:17PM -0300, Marcelo Ricardo Leitner wrote:
> syzbot reported an use-after-free involving sctp_id2asoc.  Dmitry Vyukov
> helped to root cause it and it is because of reading the asoc after it
> was freed:
> 
>         CPU 1                       CPU 2
> (working on socket 1)            (working on socket 2)
> 	                         sctp_association_destroy
> sctp_id2asoc
>    spin lock
>      grab the asoc from idr
>    spin unlock
>                                    spin lock
> 				     remove asoc from idr
> 				   spin unlock
> 				   free(asoc)
>    if asoc->base.sk != sk ... [*]
> 
> This can only be hit if trying to fetch asocs from different sockets. As
> we have a single IDR for all asocs, in all SCTP sockets, their id is
> unique on the system. An application can try to send stuff on an id
> that matches on another socket, and the if in [*] will protect from such
> usage. But it didn't consider that as that asoc may belong to another
> socket, it may be freed in parallel (read: under another socket lock).
> 
> We fix it by moving the checks in [*] into the protected region. This
> fixes it because the asoc cannot be freed while the lock is held.
> 
> Reported-by: syzbot+c7dd55d7aec49d48e49a@syzkaller.appspotmail.com
> Acked-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
> ---
>  net/sctp/socket.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index f73e9d38d5ba734d7ee3347e4015fd30d355bbfa..a7722f43aa69801c31409d4914c99946ee5533f5 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -271,11 +271,10 @@ struct sctp_association *sctp_id2assoc(struct sock *sk, sctp_assoc_t id)
>  
>  	spin_lock_bh(&sctp_assocs_id_lock);
>  	asoc = (struct sctp_association *)idr_find(&sctp_assocs_id, (int)id);
> +	if (asoc && (asoc->base.sk != sk || asoc->base.dead))
> +		asoc = NULL;
>  	spin_unlock_bh(&sctp_assocs_id_lock);
>  
> -	if (!asoc || (asoc->base.sk != sk) || asoc->base.dead)
> -		return NULL;
> -
>  	return asoc;
>  }
>  
> -- 
> 2.17.1
> 
> 
Acked-by: Neil Horman <nhorman@tuxdriver.com>

Re: [PATCH net] sctp: fix race on sctp_id2asoc

[Neil Horman]

On Tue, Oct 16, 2018 at 03:18:17PM -0300, Marcelo Ricardo Leitner wrote:
> syzbot reported an use-after-free involving sctp_id2asoc.  Dmitry Vyukov
> helped to root cause it and it is because of reading the asoc after it
> was freed:
> 
>         CPU 1                       CPU 2
> (working on socket 1)            (working on socket 2)
> 	                         sctp_association_destroy
> sctp_id2asoc
>    spin lock
>      grab the asoc from idr
>    spin unlock
>                                    spin lock
> 				     remove asoc from idr
> 				   spin unlock
> 				   free(asoc)
>    if asoc->base.sk != sk ... [*]
> 
> This can only be hit if trying to fetch asocs from different sockets. As
> we have a single IDR for all asocs, in all SCTP sockets, their id is
> unique on the system. An application can try to send stuff on an id
> that matches on another socket, and the if in [*] will protect from such
> usage. But it didn't consider that as that asoc may belong to another
> socket, it may be freed in parallel (read: under another socket lock).
> 
> We fix it by moving the checks in [*] into the protected region. This
> fixes it because the asoc cannot be freed while the lock is held.
> 
> Reported-by: syzbot+c7dd55d7aec49d48e49a@syzkaller.appspotmail.com
> Acked-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
> ---
>  net/sctp/socket.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index f73e9d38d5ba734d7ee3347e4015fd30d355bbfa..a7722f43aa69801c31409d4914c99946ee5533f5 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -271,11 +271,10 @@ struct sctp_association *sctp_id2assoc(struct sock *sk, sctp_assoc_t id)
>  
>  	spin_lock_bh(&sctp_assocs_id_lock);
>  	asoc = (struct sctp_association *)idr_find(&sctp_assocs_id, (int)id);
> +	if (asoc && (asoc->base.sk != sk || asoc->base.dead))
> +		asoc = NULL;
>  	spin_unlock_bh(&sctp_assocs_id_lock);
>  
> -	if (!asoc || (asoc->base.sk != sk) || asoc->base.dead)
> -		return NULL;
> -
>  	return asoc;
>  }
>  
> -- 
> 2.17.1
> 
> 
Acked-by: Neil Horman <nhorman@tuxdriver.com>

Re: [PATCH net] sctp: fix race on sctp_id2asoc

[David Miller]

From: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Date: Tue, 16 Oct 2018 15:18:17 -0300

> syzbot reported an use-after-free involving sctp_id2asoc.  Dmitry Vyukov
> helped to root cause it and it is because of reading the asoc after it
> was freed:
> 
>         CPU 1                       CPU 2
> (working on socket 1)            (working on socket 2)
> 	                         sctp_association_destroy
> sctp_id2asoc
>    spin lock
>      grab the asoc from idr
>    spin unlock
>                                    spin lock
> 				     remove asoc from idr
> 				   spin unlock
> 				   free(asoc)
>    if asoc->base.sk != sk ... [*]
> 
> This can only be hit if trying to fetch asocs from different sockets. As
> we have a single IDR for all asocs, in all SCTP sockets, their id is
> unique on the system. An application can try to send stuff on an id
> that matches on another socket, and the if in [*] will protect from such
> usage. But it didn't consider that as that asoc may belong to another
> socket, it may be freed in parallel (read: under another socket lock).
> 
> We fix it by moving the checks in [*] into the protected region. This
> fixes it because the asoc cannot be freed while the lock is held.
> 
> Reported-by: syzbot+c7dd55d7aec49d48e49a@syzkaller.appspotmail.com
> Acked-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

Applied and queued up for -stable.

Re: [PATCH net] sctp: fix race on sctp_id2asoc

[David Miller]

From: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Date: Tue, 16 Oct 2018 15:18:17 -0300

> syzbot reported an use-after-free involving sctp_id2asoc.  Dmitry Vyukov
> helped to root cause it and it is because of reading the asoc after it
> was freed:
> 
>         CPU 1                       CPU 2
> (working on socket 1)            (working on socket 2)
> 	                         sctp_association_destroy
> sctp_id2asoc
>    spin lock
>      grab the asoc from idr
>    spin unlock
>                                    spin lock
> 				     remove asoc from idr
> 				   spin unlock
> 				   free(asoc)
>    if asoc->base.sk != sk ... [*]
> 
> This can only be hit if trying to fetch asocs from different sockets. As
> we have a single IDR for all asocs, in all SCTP sockets, their id is
> unique on the system. An application can try to send stuff on an id
> that matches on another socket, and the if in [*] will protect from such
> usage. But it didn't consider that as that asoc may belong to another
> socket, it may be freed in parallel (read: under another socket lock).
> 
> We fix it by moving the checks in [*] into the protected region. This
> fixes it because the asoc cannot be freed while the lock is held.
> 
> Reported-by: syzbot+c7dd55d7aec49d48e49a@syzkaller.appspotmail.com
> Acked-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

Applied and queued up for -stable.