linux-kernel - [PATCH 4.9 31/65] netlink: put module reference if dump start fails

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Date:   Fri,  9 Mar 2018 16:18:31 -0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, "Jason A. Donenfeld" <Jason@...c4.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.9 31/65] netlink: put module reference if dump start fails

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

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

From: Jason A. Donenfeld <Jason@...c4.com>

commit b87b6194be631c94785fe93398651e804ed43e28 upstream.

Before, if cb->start() failed, the module reference would never be put,
because cb->cb_running is intentionally false at this point. Users are
generally annoyed by this because they can no longer unload modules that
leak references. Also, it may be possible to tediously wrap a reference
counter back to zero, especially since module.c still uses atomic_inc
instead of refcount_inc.

This patch expands the error path to simply call module_put if
cb->start() fails.

Fixes: 41c87425a1ac ("netlink: do not set cb_running if dump's start() errs")
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/netlink/af_netlink.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2258,7 +2258,7 @@ int __netlink_dump_start(struct sock *ss
 	if (cb->start) {
 		ret = cb->start(cb);
 		if (ret)
-			goto error_unlock;
+			goto error_put;
 	}

 	nlk->cb_running = true;
@@ -2278,6 +2278,8 @@ int __netlink_dump_start(struct sock *ss
 	 */
 	return -EINTR;

+error_put:
+	module_put(control->module);
 error_unlock:
 	sock_put(sk);
 	mutex_unlock(nlk->cb_mutex);