netlink: hold nlk->cb_mutex longer in __netlink_dump_start()

__netlink_dump_start() releases nlk->cb_mutex right before
calling netlink_dump() which grabs it again.

This seems dangerous, even if KASAN did not bother yet.

Add a @lock_taken parameter to netlink_dump() to let it
grab the mutex if called from netlink_recvmsg() only.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 9c96234..94f3860 100644 (file)
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -130,7 +130,7 @@ static const char *const nlk_cb_mutex_key_strings[MAX_LINKS + 1] = {
        "nlk_cb_mutex-MAX_LINKS"
 };
 
-static int netlink_dump(struct sock *sk);
+static int netlink_dump(struct sock *sk, bool lock_taken);
 
 /* nl_table locking explained:
  * Lookup and traversal are protected with an RCU read-side lock. Insertion
@@ -1987,7 +1987,7 @@ static int netlink_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 
        if (READ_ONCE(nlk->cb_running) &&
            atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf / 2) {
-               ret = netlink_dump(sk);
+               ret = netlink_dump(sk, false);
                if (ret) {
                        WRITE_ONCE(sk->sk_err, -ret);
                        sk_error_report(sk);
@@ -2196,7 +2196,7 @@ static int netlink_dump_done(struct netlink_sock *nlk, struct sk_buff *skb,
        return 0;
 }
 
-static int netlink_dump(struct sock *sk)
+static int netlink_dump(struct sock *sk, bool lock_taken)
 {
        struct netlink_sock *nlk = nlk_sk(sk);
        struct netlink_ext_ack extack = {};
@@ -2208,7 +2208,8 @@ static int netlink_dump(struct sock *sk)
        int alloc_min_size;
        int alloc_size;
 
-       mutex_lock(nlk->cb_mutex);
+       if (!lock_taken)
+               mutex_lock(nlk->cb_mutex);
        if (!nlk->cb_running) {
                err = -EINVAL;
                goto errout_skb;
@@ -2365,9 +2366,7 @@ int __netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
        WRITE_ONCE(nlk->cb_running, true);
        nlk->dump_done_errno = INT_MAX;
 
-       mutex_unlock(nlk->cb_mutex);
-
-       ret = netlink_dump(sk);
+       ret = netlink_dump(sk, true);
 
        sock_put(sk);