netdev - question about klen in move_addr_to

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Message-ID: <20130318101007.GO9189@mwanda>
Date:	Mon, 18 Mar 2013 13:10:07 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	netdev@...r.kernel.org
Subject: question about klen in move_addr_to_user()

Smatch complains that about a potential buffer overflow in
move_add_to_user()

net/socket.c
   212  static int move_addr_to_user(struct sockaddr_storage *kaddr, int klen,
   213                               void __user *uaddr, int __user *ulen)
   214  {
   215          int err;
   216          int len;
   217  
   218          err = get_user(len, ulen);
   219          if (err)
   220                  return err;
   221          if (len > klen)
   222                  len = klen;
   223          if (len < 0 || len > sizeof(struct sockaddr_storage))
   224                  return -EINVAL;
   225          if (len) {
   226                  if (audit_sockaddr(klen, kaddr))
                                           ^^^^
Smatch complains that although "len" is capped here, "klen" hasn't
necessarily been.  If "klen" is more than 128 bytes it leads to
memory corruption.

   227                          return -ENOMEM;
   228                  if (copy_to_user(uaddr, kaddr, len))
   229                          return -EFAULT;
   230          }

The call tree is this:

__sys_recvmsg() gets the msg->msg_namelen from the user.

Normally the network protocols set msg->msg_namelen in their
->recvmsg() function but some don't like caif_seqpkt_recvmsg() and
recv_msg() for tipc.

regards,
dan carpenter

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