Re: [PATCH 2/3] tun: free skb in early errors

[Jason Wang]

On 2017年12月01日 13:54, w...@redhat.com wrote:
From: Wei Xu <w...@redhat.com>

tun_recvmsg() supports accepting skb by msg_control after
commit ac77cfd4258f ("tun: support receiving skb through msg_control"),
the skb if presented should be freed within the function, otherwise it
would be leaked.

Signed-off-by: Wei Xu <w...@redhat.com>
Reported-by: Matthew Rosato <mjros...@linux.vnet.ibm.com>
---
  drivers/net/tun.c | 14 +++++++++++---
  1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 6a7bde9..5563430 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2067,14 +2067,17 @@ static int tun_recvmsg(struct socket *sock, struct 
msghdr *m, size_t total_len,
  {
        struct tun_file *tfile = container_of(sock, struct tun_file, socket);
        struct tun_struct *tun = tun_get(tfile);
+       struct sk_buff *skb = m->msg_control;
        int ret;
  
-	if (!tun)
-               return -EBADFD;
+       if (!tun) {
+               ret = -EBADFD;
+               goto out_free_skb;

Unfortunately, you can't to there since tun is NULL.


+       }
  
  	if (flags & ~(MSG_DONTWAIT|MSG_TRUNC|MSG_ERRQUEUE)) {
                ret = -EINVAL;
-               goto out;
+               goto out_free_skb;
        }
        if (flags & MSG_ERRQUEUE) {
                ret = sock_recv_errqueue(sock->sk, m, total_len,
@@ -2087,6 +2090,11 @@ static int tun_recvmsg(struct socket *sock, struct 
msghdr *m, size_t total_len,
                m->msg_flags |= MSG_TRUNC;
                ret = flags & MSG_TRUNC ? ret : total_len;
        }
+       goto out;

We usually don't use goto in the case of success, and you need deal with 
the case skb != NULL but iov_iter_count(to) == 0 in tun_do_read().

Thanks

+
+out_free_skb:
+       if (skb)
+               kfree_skb(skb);
  out:
        tun_put(tun);
        return ret;