[PATCH] pid: replace is_orphaned_pgrp with is_current_pgrp_orphaned

Every call to is_orphaned_pgrp passed in process_group(current) which is racy
with respect to another thread changing our process group.  It didn't bite us
because we were dealing with integers and the worse we would get would be a
stale answer.

In switching the checks to use struct pid to be a little more efficient and
prepare the way for pid namespaces this race became apparent.

So I simplified the calls to the more specialized is_current_pgrp_orphaned so
I didn't have to worry about making logic changes to avoid the race.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

5 files changed, 6 insertions, 6 deletions

diff --git a/drivers/char/n_tty.c b/drivers/char/n_tty.c
index 2bdb0144a22e..c035c2f1f462 100644
--- a/drivers/char/n_tty.c
+++ b/drivers/char/n_tty.c
@@ -1188,7 +1188,7 @@ static int job_control(struct tty_struct *tty, struct file *file)
                         printk("read_chan: tty->pgrp <= 0!\n");
                 else if (process_group(current) != tty->pgrp) {
                         if (is_ignored(SIGTTIN) ||
-                            is_orphaned_pgrp(process_group(current)))
+                            is_current_pgrp_orphaned())
                                 return -EIO;
                         kill_pg(process_group(current), SIGTTIN, 1);
                         return -ERESTARTSYS;
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 95f3596189cf..94070f7bf389 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1118,7 +1118,7 @@ int tty_check_change(struct tty_struct * tty)
                 return 0;
         if (is_ignored(SIGTTOU))
                 return 0;
-        if (is_orphaned_pgrp(process_group(current)))
+        if (is_current_pgrp_orphaned())
                 return -EIO;
         (void) kill_pg(process_group(current), SIGTTOU, 1);
         return -ERESTARTSYS;
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 0a10a4e7bbc3..d0e03c4a71b1 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -303,7 +303,7 @@ extern int tty_read_raw_data(struct tty_struct *tty, unsigned char *bufp,
                              int buflen);
 extern void tty_write_message(struct tty_struct *tty, char *msg);
 
-extern int is_orphaned_pgrp(int pgrp);
+extern int is_current_pgrp_orphaned(void);
 extern int is_ignored(int sig);
 extern int tty_signal(int sig, struct tty_struct *tty);
 extern void tty_hangup(struct tty_struct * tty);
diff --git a/kernel/exit.c b/kernel/exit.c
index 407b80aaefda..f132349c0325 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -229,12 +229,12 @@ static int will_become_orphaned_pgrp(struct pid *pgrp, struct task_struct *ignor
         return ret;     /* (sighing) "Often!" */
 }
 
-int is_orphaned_pgrp(int pgrp)
+int is_current_pgrp_orphaned(void)
 {
         int retval;
 
         read_lock(&tasklist_lock);
-        retval = will_become_orphaned_pgrp(find_pid(pgrp), NULL);
+        retval = will_become_orphaned_pgrp(task_pgrp(current), NULL);
         read_unlock(&tasklist_lock);
 
         return retval;
diff --git a/kernel/signal.c b/kernel/signal.c
index de66def71644..a9b679ed795c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1909,7 +1909,7 @@ relock:
 
                                 /* signals can be posted during this window */
 
-                                if (is_orphaned_pgrp(process_group(current)))
+                                if (is_current_pgrp_orphaned())
                                         goto relock;
 
                                 spin_lock_irq(&current->sighand->siglock);