net/3com/3c515: Fix timer handling, prevent leaks and crashes

[Thomas Gleixner]

The timer handling in this driver is broken in several ways:

- corkscrew_open() initializes and arms a timer before requesting the
  device interrupt. If the request fails the timer stays armed.

  A second call to corkscrew_open will unconditionally reinitialize the
  quued timer and arm it again. Also a immediate device removal will leave
  the timer queued because close() is not called (open() failed) and
  therefore nothing issues del_timer().

  The reinitialization corrupts the link chain in the timer wheel hash
  bucket and causes a NULL pointer dereference when the timer wheel tries
  to operate on that hash bucket. Immediate device removal lets the link
  chain poke into freed and possibly reused memory.

  Solution: Arm the timer after the successful irq request.

- corkscrew_close() uses del_timer()

  On close the timer is disarmed with del_timer() which lets the following
  code race against a concurrent timer expiry function.

  Solution: Use del_timer_sync() instead

- corkscrew_close() calls del_timer() unconditionally

  del_timer() is invoked even if the timer was never initialized. This
  works by chance because the struct containing the timer is zeroed at
  allocation time.

  Solution: Move the setup of the timer into corkscrew_setup().

Reported-by: Matthew Whitehead <tedheads...@gmail.com>
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Cc: Andy Lutomirski <l...@kernel.org>
Cc: net...@vger.kernel.org
---
 drivers/net/ethernet/3com/3c515.c |   15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

--- a/drivers/net/ethernet/3com/3c515.c
+++ b/drivers/net/ethernet/3com/3c515.c
@@ -628,6 +628,8 @@ static int corkscrew_setup(struct net_de
 
        spin_lock_init(&vp->lock);
 
+       setup_timer(&vp->timer, corkscrew_timer, (unsigned long) dev);
+
        /* Read the station address from the EEPROM. */
        EL3WINDOW(0);
        for (i = 0; i < 0x18; i++) {
@@ -708,6 +710,7 @@ static int corkscrew_open(struct net_dev
 {
        int ioaddr = dev->base_addr;
        struct corkscrew_private *vp = netdev_priv(dev);
+       bool armtimer = false;
        __u32 config;
        int i;
 
@@ -732,12 +735,7 @@ static int corkscrew_open(struct net_dev
                if (corkscrew_debug > 1)
                        pr_debug("%s: Initial media type %s.\n",
                               dev->name, media_tbl[dev->if_port].name);
-
-               init_timer(&vp->timer);
-               vp->timer.expires = jiffies + media_tbl[dev->if_port].wait;
-               vp->timer.data = (unsigned long) dev;
-               vp->timer.function = corkscrew_timer;   /* timer handler */
-               add_timer(&vp->timer);
+               armtimer = true;
        } else
                dev->if_port = vp->default_media;
 
@@ -777,6 +775,9 @@ static int corkscrew_open(struct net_dev
                return -EAGAIN;
        }
 
+       if (armtimer)
+               mod_timer(&vp->timer, jiffies + media_tbl[dev->if_port].wait);
+
        if (corkscrew_debug > 1) {
                EL3WINDOW(4);
                pr_debug("%s: corkscrew_open() irq %d media status %4.4x.\n",
@@ -1427,7 +1428,7 @@ static int corkscrew_close(struct net_de
                        dev->name, rx_nocopy, rx_copy, queued_packet);
        }
 
-       del_timer(&vp->timer);
+       del_timer_sync(&vp->timer);
 
        /* Turn off statistics ASAP.  We update lp->stats below. */
        outw(StatsDisable, ioaddr + EL3_CMD);