linux-kernel - [PATCH 3.14 071/130] RDS: fix race condition when sending a message on unbound socket

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Message-Id: <20160301234502.310110398@linuxfoundation.org>
Date:	Tue, 01 Mar 2016 23:51:15 +0000
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	<linux-kernel@...r.kernel.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<stable@...r.kernel.org>, Vegard Nossum <vegard.nossum@...cle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Santosh Shilimkar <santosh.shilimkar@...cle.com>,
	Quentin Casasnovas <quentin.casasnovas@...cle.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.14 071/130] RDS: fix race condition when sending a message on unbound socket

3.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Quentin Casasnovas <quentin.casasnovas@...cle.com>

commit 8c7188b23474cca017b3ef354c4a58456f68303a upstream.

Sasha's found a NULL pointer dereference in the RDS connection code when
sending a message to an apparently unbound socket.  The problem is caused
by the code checking if the socket is bound in rds_sendmsg(), which checks
the rs_bound_addr field without taking a lock on the socket.  This opens a
race where rs_bound_addr is temporarily set but where the transport is not
in rds_bind(), leading to a NULL pointer dereference when trying to
dereference 'trans' in __rds_conn_create().

Vegard wrote a reproducer for this issue, so kindly ask him to share if
you're interested.

I cannot reproduce the NULL pointer dereference using Vegard's reproducer
with this patch, whereas I could without.

Complete earlier incomplete fix to CVE-2015-6937:

  74e98eb08588 ("RDS: verify the underlying transport exists before creating a connection")

Reviewed-by: Vegard Nossum <vegard.nossum@...cle.com>
Reviewed-by: Sasha Levin <sasha.levin@...cle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@...cle.com>
Signed-off-by: Quentin Casasnovas <quentin.casasnovas@...cle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/rds/connection.c |    6 ------
 net/rds/send.c       |    4 +++-
 2 files changed, 3 insertions(+), 7 deletions(-)

--- a/net/rds/connection.c
+++ b/net/rds/connection.c
@@ -189,12 +189,6 @@ static struct rds_connection *__rds_conn
 		goto out;
 	}

-	if (trans == NULL) {
-		kmem_cache_free(rds_conn_slab, conn);
-		conn = ERR_PTR(-ENODEV);
-		goto out;
-	}
-
 	conn->c_trans = trans;

 	ret = trans->conn_alloc(conn, gfp);
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -955,11 +955,13 @@ int rds_sendmsg(struct kiocb *iocb, stru
 		release_sock(sk);
 	}

-	/* racing with another thread binding seems ok here */
+	lock_sock(sk);
 	if (daddr == 0 || rs->rs_bound_addr == 0) {
+		release_sock(sk);
 		ret = -ENOTCONN; /* XXX not a great errno */
 		goto out;
 	}
+	release_sock(sk);

 	/* size of rm including all sgs */
 	ret = rds_rm_size(msg, payload_len);