Fix hole where tty structure can be released when reference
count is non zero. Existing code can sleep without tty_sem
protection between deciding to release the tty structure
(setting local variables tty_closing and otty_closing)
and setting TTY_CLOSING to prevent further opens.
An open can occur during this interval causing release_dev()
to free the tty structure while it is still referenced.
This should fix bugzilla.kernel.org
[Bug 6041] New: Unable to handle kernel paging request
In Bug 6041, tty_open() oopes on accessing the tty structure
it has successfully claimed. Bug was on SMP machine
with the same tty being opened and closed by
multiple processes, and DEBUG_PAGEALLOC enabled.
Signed-off-by: Paul Fulghum <[email protected]>
Cc: Alan Cox <[email protected]>
Cc: Jesper Juhl <[email protected]>
--- linux/drivers/char/tty_io.c 2006-02-10 15:54:00.000000000 -0600
+++ b/drivers/char/tty_io.c 2006-02-13 13:14:33.000000000 -0600
@@ -1841,7 +1841,6 @@ static void release_dev(struct file * fi
tty_closing = tty->count <= 1;
o_tty_closing = o_tty &&
(o_tty->count <= (pty_master ? 1 : 0));
- up(&tty_sem);
do_sleep = 0;
if (tty_closing) {
@@ -1869,6 +1868,7 @@ static void release_dev(struct file * fi
printk(KERN_WARNING "release_dev: %s: read/write wait queue "
"active!\n", tty_name(tty, buf));
+ up(&tty_sem);
schedule();
}
@@ -1877,8 +1877,6 @@ static void release_dev(struct file * fi
* both sides, and we've completed the last operation that could
* block, so it's safe to proceed with closing.
*/
-
- down(&tty_sem);
if (pty_master) {
if (--o_tty->count < 0) {
printk(KERN_WARNING "release_dev: bad pty slave count "
@@ -1892,7 +1890,6 @@ static void release_dev(struct file * fi
tty->count, tty_name(tty, buf));
tty->count = 0;
}
- up(&tty_sem);
/*
* We've decremented tty->count, so we need to remove this file
@@ -1937,6 +1934,8 @@ static void release_dev(struct file * fi
read_unlock(&tasklist_lock);
}
+ up(&tty_sem);
+
/* check whether both sides are closing ... */
if (!tty_closing || (o_tty && !o_tty_closing))
return;
-
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