Subject: patch "TTY: hvc, fix TTY refcounting" added to tty tree

From: <[email-masked]>
Date: Fri, 13 Apr 2012 10:54:55 -0700

This is a note to let you know that I've just added the patch titled

    TTY: hvc, fix TTY refcounting

to my tty git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-next branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will also will be merged in the next major kernel release
during the merge window.

If you have any questions about this process, please let me know.

>>From a2f892060f174e5f90041167ca00eb9e68badcb8 Mon Sep 17 00:00:00 2001
From: Jiri Slaby <[email-masked]>
Date: Fri, 13 Apr 2012 10:31:32 +0200
Subject: TTY: hvc, fix TTY refcounting

A -next commit "TTY: HVC, use tty from tty_port" switched the driver
to use tty_port helper for tty refcounting. But it omitted to remove
manual tty refcounting from open, close and hangup. So now we are
getting random crashes caused by use-after-free:
Unable to handle kernel paging request for data at address 0xc0000003f9d550
Faulting instruction address: 0xc0000000001b7f40
Oops: Kernel access of bad area, sig: 11 [#1]
...
NIP: c0000000001b7f40 LR: c0000000001b7f14 CTR: c0000000000e04f0
...
NIP [c0000000001b7f40] .__kmalloc+0x70/0x230
LR [c0000000001b7f14] .__kmalloc+0x44/0x230
Call Trace:
[c0000003f68bf930] [c0000003f68bf9b0] 0xc0000003f68bf9b0 (unreliable)
[c0000003f68bf9e0] [c0000000001e5424] .alloc_fdmem+0x24/0x70
[c0000003f68bfa60] [c0000000001e54f8] .alloc_fdtable+0x88/0x130
[c0000003f68bfaf0] [c0000000001e5924] .dup_fd+0x384/0x450
[c0000003f68bfbd0] [c00000000009a310] .copy_process+0x880/0x11d0
[c0000003f68bfcd0] [c00000000009aee0] .do_fork+0x70/0x400
[c0000003f68bfdc0] [c0000000000141c4] .sys_clone+0x54/0x70
[c0000003f68bfe30] [c000000000009aa0] .ppc_clone+0x8/0xc

Fix that by complete removal of tty_kref_get/put in open/close/hangup
paths.

Signed-off-by: Jiri Slaby <[email-masked]>
Reported-and-tested-by: Michael Neuling <[email-masked]>
Cc: Stephen Rothwell <[email-masked]>
Cc: ppc-dev <[email-masked]>
Signed-off-by: Greg Kroah-Hartman <[email-masked]>
---
 drivers/tty/hvc/hvc_console.c |    5 -----
 1 file changed, 5 deletions(-)

diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index 6c45cbf..2d691eb 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -317,8 +317,6 @@ static int hvc_open(struct tty_struct *tty, struct file * filp)
 	/* Check and then increment for fast path open. */
 	if (hp->port.count++ > 0) {
 		spin_unlock_irqrestore(&hp->port.lock, flags);
-		/* FIXME why taking a reference here? */
-		tty_kref_get(tty);
 		hvc_kick();
 		return 0;
 	} /* else count == 0 */
@@ -338,7 +336,6 @@ static int hvc_open(struct tty_struct *tty, struct file * filp)
 	 */
 	if (rc) {
 		tty_port_tty_set(&hp->port, NULL);
-		tty_kref_put(tty);
 		tty->driver_data = NULL;
 		tty_port_put(&hp->port);
 		printk(KERN_ERR "hvc_open: request_irq failed with rc %d.\n", rc);
@@ -393,7 +390,6 @@ static void hvc_close(struct tty_struct *tty, struct file * filp)
 		spin_unlock_irqrestore(&hp->port.lock, flags);
 	}
 
-	tty_kref_put(tty);
 	tty_port_put(&hp->port);
 }
 
@@ -433,7 +429,6 @@ static void hvc_hangup(struct tty_struct *tty)
 
 	while(temp_open_count) {
 		--temp_open_count;
-		tty_kref_put(tty);
 		tty_port_put(&hp->port);
 	}
 }
-- 
1.7.10