[PATCH 4.9 072/105] netlink: do not proceed if dumps start() errs

[Greg Kroah-Hartman]

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

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

From: "Jason A. Donenfeld" <Jason@xxxxxxxxx>


[ Upstream commit fef0035c0f31322d417d1954bba5ab959bf91183 ]

Drivers that use the start method for netlink dumping rely on dumpit not
being called if start fails. For example, ila_xlat.c allocates memory
and assigns it to cb->args[0] in its start() function. It might fail to
do that and return -ENOMEM instead. However, even when returning an
error, dumpit will be called, which, in the example above, quickly
dereferences the memory in cb->args[0], which will OOPS the kernel. This
is but one example of how this goes wrong.

Since start() has always been a function with an int return type, it
therefore makes sense to use it properly, rather than ignoring it. This
patch thus returns early and does not call dumpit() when start() fails.

Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
Cc: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
Reviewed-by: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/netlink/af_netlink.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2211,10 +2211,13 @@ int __netlink_dump_start(struct sock *ss
 
 	mutex_unlock(nlk->cb_mutex);
 
+	ret = 0;
 	if (cb->start)
-		cb->start(cb);
+		ret = cb->start(cb);
+
+	if (!ret)
+		ret = netlink_dump(sk);
 
-	ret = netlink_dump(sk);
 	sock_put(sk);
 
 	if (ret)