[PATCH] n_r3964: Use struct pid to track user space clients

Currently this driver tracks user space clients it should send signals to. In
the presenct of file descriptor passing this is appears susceptible to
confusion from pid wrap around issues.

Replacing this with a struct pid prevents us from getting confused, and
prepares for a pid namespace implementation.

Signed-off-by: Eric W. Biederman <[e-mail]>
Cc: David Woodhouse <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/char/n_r3964.c

···
 static void receive_char(struct r3964_info *pInfo, const unsigned char c);
 static void receive_error(struct r3964_info *pInfo, const char flag);
 static void on_timeout(unsigned long priv);
-static int enable_signals(struct r3964_info *pInfo, pid_t pid, int arg);
-static int read_telegram(struct r3964_info *pInfo, pid_t pid, unsigned char __user *buf);
+static int enable_signals(struct r3964_info *pInfo, struct pid *pid, int arg);
+static int read_telegram(struct r3964_info *pInfo, struct pid *pid, unsigned char __user *buf);
 static void add_msg(struct r3964_client_info *pClient, int msg_id, int arg,
              int error_code, struct r3964_block_header *pBlock);
 static struct r3964_message* remove_msg(struct r3964_info *pInfo, 
···
 }
 
 static struct r3964_client_info *findClient(
-  struct r3964_info *pInfo, pid_t pid)
+  struct r3964_info *pInfo, struct pid *pid)
 {
    struct r3964_client_info *pClient;
    
···
    return NULL;
 }
 
-static int enable_signals(struct r3964_info *pInfo, pid_t pid, int arg)
+static int enable_signals(struct r3964_info *pInfo, struct pid *pid, int arg)
 {
    struct r3964_client_info *pClient;
    struct r3964_client_info **ppClient;
···
          
          if(pClient->pid == pid)
          {
-            TRACE_PS("removing client %d from client list", pid);
+            TRACE_PS("removing client %d from client list", pid_nr(pid));
             *ppClient = pClient->next;
             while(pClient->msg_count)
             {
···
                   TRACE_M("enable_signals - msg kfree %p",pMsg);
                }
             }
+	    put_pid(pClient->pid);
             kfree(pClient);
             TRACE_M("enable_signals - kfree %p",pClient);
             return 0;
···
          if(pClient==NULL)
             return -ENOMEM;
 
-         TRACE_PS("add client %d to client list", pid);
+         TRACE_PS("add client %d to client list", pid_nr(pid));
 	 spin_lock_init(&pClient->lock);
          pClient->sig_flags=arg;
-         pClient->pid = pid;
+         pClient->pid = get_pid(pid);
          pClient->next=pInfo->firstClient;
          pClient->first_msg = NULL;
          pClient->last_msg = NULL;
···
    return 0;
 }
 
-static int read_telegram(struct r3964_info *pInfo, pid_t pid, unsigned char __user *buf)
+static int read_telegram(struct r3964_info *pInfo, struct pid *pid, unsigned char __user *buf)
 {
     struct r3964_client_info *pClient;
     struct r3964_block_header *block;
···
    /* Send SIGIO signal to client process: */
    if(pClient->sig_flags & R3964_USE_SIGIO)
    {
-      kill_proc(pClient->pid, SIGIO, 1);
+      kill_pid(pClient->pid, SIGIO, 1);
    }
 }
 
···
 {
     struct r3964_block_header *block;
 
-    TRACE_PS("remove_client_block PID %d", pClient->pid);
+    TRACE_PS("remove_client_block PID %d", pid_nr(pClient->pid));
 
     block=pClient->next_block_to_read;
     if(block)
···
              TRACE_M("r3964_close - msg kfree %p",pMsg);
           }
        }
+       put_pid(pClient->pid);
        kfree(pClient);
        TRACE_M("r3964_close - client kfree %p",pClient);
        pClient=pNext;
···
    struct r3964_client_message theMsg;
    DECLARE_WAITQUEUE (wait, current);
    
-   int pid = current->pid;
    int count;
    
    TRACE_L("read()");
  
-   pClient=findClient(pInfo, pid);
+   pClient=findClient(pInfo, task_pid(current));
    if(pClient)
    {
       pMsg = remove_msg(pInfo, pClient);
···
    struct r3964_block_header *pHeader;
    struct r3964_client_info *pClient;
    unsigned char *new_data;
-   int pid;
    
    TRACE_L("write request, %d characters", count);
 /* 
···
    pHeader->locks = 0;
    pHeader->owner = NULL;
    
-   pid=current->pid;
-   
-   pClient=findClient(pInfo, pid);
+   pClient=findClient(pInfo, task_pid(current));
    if(pClient)
    {
       pHeader->owner = pClient;
···
    switch(cmd)
    {
       case R3964_ENABLE_SIGNALS:
-         return enable_signals(pInfo, current->pid, arg);
+         return enable_signals(pInfo, task_pid(current), arg);
       case R3964_SETPRIORITY:
          if(arg<R3964_MASTER || arg>R3964_SLAVE)
             return -EINVAL;
···
             pInfo->flags &= ~R3964_BCC;
          return 0;
       case R3964_READ_TELEGRAM:
-         return read_telegram(pInfo, current->pid, (unsigned char __user *)arg);
+         return read_telegram(pInfo, task_pid(current), (unsigned char __user *)arg);
       default:
          return -ENOIOCTLCMD;
    }
···
 		      struct poll_table_struct *wait)
 {
    struct r3964_info *pInfo=(struct r3964_info*)tty->disc_data;
-   int pid=current->pid;
    struct r3964_client_info *pClient;
    struct r3964_message *pMsg=NULL;
    unsigned long flags;
···
 
    TRACE_L("POLL");
 
-   pClient=findClient(pInfo,pid);
+   pClient=findClient(pInfo, task_pid(current));
    if(pClient)
      {
        poll_wait(file, &pInfo->read_wait, wait);

include/linux/n_r3964.h

···
 
 struct r3964_client_info {
 	spinlock_t     lock;
-	pid_t          pid;
+	struct pid    *pid;
 	unsigned int   sig_flags;
 
 	struct r3964_client_info *next;