[PATCHv2 net] sctp: hold transport before accessing its asoc in sctp_hash_transport

[PATCHv2 net] sctp: hold transport before accessing its asoc in sctp_hash_transport

[Xin Long]

In sctp_hash_transport, it dereferences a transport's asoc only under
rcu_read_lock. Without holding the transport, its asoc could be freed
already, which leads to a use-after-free panic.

A similar fix as Commit bab1be79a516 ("sctp: hold transport before
accessing its asoc in sctp_transport_get_next") is needed to hold
the transport before accessing its asoc in sctp_hash_transport.

Note that as rhlist keeps the lists to a small size, this extra
atomic operation won't cause a noticeable latency on inserting
a transport. Yet it's not in a datapath.

v1->v2:
  - improve the changelog.

Fixes: cd2b70875058 ("sctp: check duplicate node before inserting a new transport")
Reported-by: syzbot+0b05d8aa7cb185107483@syzkaller.appspotmail.com
Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 net/sctp/input.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/sctp/input.c b/net/sctp/input.c
index ce7351c..c2c0816 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -896,11 +896,16 @@ int sctp_hash_transport(struct sctp_transport *t)
 	list = rhltable_lookup(&sctp_transport_hashtable, &arg,
 			       sctp_hash_params);
 
-	rhl_for_each_entry_rcu(transport, tmp, list, node)
+	rhl_for_each_entry_rcu(transport, tmp, list, node) {
+		if (!sctp_transport_hold(transport))
+			continue;
 		if (transport->asoc->ep == t->asoc->ep) {
+			sctp_transport_put(transport);
 			rcu_read_unlock();
 			return -EEXIST;
 		}
+		sctp_transport_put(transport);
+	}
 	rcu_read_unlock();
 
 	err = rhltable_insert_key(&sctp_transport_hashtable, &arg,
-- 
2.1.0

Re: [PATCHv2 net] sctp: hold transport before accessing its asoc in sctp_hash_transport

[Marcelo Ricardo Leitner]

On Thu, Nov 29, 2018 at 02:49:28PM +0800, Xin Long wrote:
> In sctp_hash_transport, it dereferences a transport's asoc only under
> rcu_read_lock. Without holding the transport, its asoc could be freed
> already, which leads to a use-after-free panic.
> 
> A similar fix as Commit bab1be79a516 ("sctp: hold transport before
> accessing its asoc in sctp_transport_get_next") is needed to hold
> the transport before accessing its asoc in sctp_hash_transport.
> 
> Note that as rhlist keeps the lists to a small size, this extra
> atomic operation won't cause a noticeable latency on inserting
> a transport. Yet it's not in a datapath.
> 
> v1->v2:
>   - improve the changelog.
> 
> Fixes: cd2b70875058 ("sctp: check duplicate node before inserting a new transport")
> Reported-by: syzbot+0b05d8aa7cb185107483@syzkaller.appspotmail.com
> Signed-off-by: Xin Long <lucien.xin@gmail.com>

Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>

> ---
>  net/sctp/input.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/net/sctp/input.c b/net/sctp/input.c
> index ce7351c..c2c0816 100644
> --- a/net/sctp/input.c
> +++ b/net/sctp/input.c
> @@ -896,11 +896,16 @@ int sctp_hash_transport(struct sctp_transport *t)
>  	list = rhltable_lookup(&sctp_transport_hashtable, &arg,
>  			       sctp_hash_params);
>  
> -	rhl_for_each_entry_rcu(transport, tmp, list, node)
> +	rhl_for_each_entry_rcu(transport, tmp, list, node) {
> +		if (!sctp_transport_hold(transport))
> +			continue;
>  		if (transport->asoc->ep == t->asoc->ep) {
> +			sctp_transport_put(transport);
>  			rcu_read_unlock();
>  			return -EEXIST;
>  		}
> +		sctp_transport_put(transport);
> +	}
>  	rcu_read_unlock();
>  
>  	err = rhltable_insert_key(&sctp_transport_hashtable, &arg,
> -- 
> 2.1.0
> 

Re: [PATCHv2 net] sctp: hold transport before accessing its asoc in sctp_hash_transport

[Neil Horman]

On Thu, Nov 29, 2018 at 02:49:28PM +0800, Xin Long wrote:
> In sctp_hash_transport, it dereferences a transport's asoc only under
> rcu_read_lock. Without holding the transport, its asoc could be freed
> already, which leads to a use-after-free panic.
> 
> A similar fix as Commit bab1be79a516 ("sctp: hold transport before
> accessing its asoc in sctp_transport_get_next") is needed to hold
> the transport before accessing its asoc in sctp_hash_transport.
> 
> Note that as rhlist keeps the lists to a small size, this extra
> atomic operation won't cause a noticeable latency on inserting
> a transport. Yet it's not in a datapath.
> 
> v1->v2:
>   - improve the changelog.
> 
> Fixes: cd2b70875058 ("sctp: check duplicate node before inserting a new transport")
> Reported-by: syzbot+0b05d8aa7cb185107483@syzkaller.appspotmail.com
> Signed-off-by: Xin Long <lucien.xin@gmail.com>
> ---
>  net/sctp/input.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/net/sctp/input.c b/net/sctp/input.c
> index ce7351c..c2c0816 100644
> --- a/net/sctp/input.c
> +++ b/net/sctp/input.c
> @@ -896,11 +896,16 @@ int sctp_hash_transport(struct sctp_transport *t)
>  	list = rhltable_lookup(&sctp_transport_hashtable, &arg,
>  			       sctp_hash_params);
>  
> -	rhl_for_each_entry_rcu(transport, tmp, list, node)
> +	rhl_for_each_entry_rcu(transport, tmp, list, node) {
> +		if (!sctp_transport_hold(transport))
> +			continue;
>  		if (transport->asoc->ep == t->asoc->ep) {
> +			sctp_transport_put(transport);
>  			rcu_read_unlock();
>  			return -EEXIST;
>  		}
> +		sctp_transport_put(transport);
> +	}
>  	rcu_read_unlock();
>  
>  	err = rhltable_insert_key(&sctp_transport_hashtable, &arg,
> -- 
> 2.1.0
> 
> 
NAK to this patch, for the same reasons as the other ones.  There is no reason
to be adding a bunch of atomic operations in this path. Please modify the
association structure to pass the kfree of the association memory through an rcu
grace period.

Neil