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SubjectRe: Slab corruption in floppy driver module
On Thu, Jan 26, 2012 at 10:05:32AM -0800, Tejun Heo wrote:
> Hello,
>
> On Thu, Jan 26, 2012 at 10:04:20AM -0500, Vivek Goyal wrote:
> > out_put_disk:
> > while (dr--) {
> > del_timer_sync(&motor_off_timer[dr]);
> > - if (disks[dr]->queue)
> > + if (disks[dr]->queue) {
> > blk_cleanup_queue(disks[dr]->queue);
> > + /*
> > + * The request queue reference we took at device
> > + * creation time has been put by above
> > + * blk_cleanup_queue(). We have not called add_disk()
> > + * yet and due to failure calling put_disk(). Put disk
> > + * will try to put a reference to disk->queue which is
> > + * taken in add_disk(). As we have not taken that
> > + * extra reference, putting extra reference down
> > + * will try to access already freed queue. Clear
> > + * disk->queue before calling put_disk().
> > + */
> > + disks[dr]->queue = NULL;
>
> Yeah, this looks correct to me. It might be better to tone down the
> comment a bit tho. Wouldn't it be sufficient to say put_disk() isn't
> paired with add_disk() and will put one extra time?

Sure. Toned down the comment as suggested. Here is the new patch.

floppy: Cleanup disk->queue before caling put_disk() if add_disk() was never called

add_disk() takes gendisk reference on request queue. If driver failed during
initialization and never called add_disk() then that extra reference is not
taken. That reference is put in put_disk(). floppy driver allocates the
disk, allocates queue, sets disk->queue and then relizes that floppy
controller is not present. It tries to tear down everything and tries to
put a reference down in put_disk() which was never taken.

In such error cases cleanup disk->queue before calling put_disk() so that
we never try to put down a reference which was never taken in first place.

Reported-by: Suresh Jayaraman <sjayaraman@suse.com>
Tested-by: Dirk Gouders <gouders@et.bocholt.fh-gelsenkirchen.de>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
---
drivers/block/floppy.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

Index: linux-2.6/drivers/block/floppy.c
===================================================================
--- linux-2.6.orig/drivers/block/floppy.c 2012-01-15 09:49:14.000000000 -0500
+++ linux-2.6/drivers/block/floppy.c 2012-01-26 14:35:14.662374464 -0500
@@ -4368,8 +4368,14 @@ out_unreg_blkdev:
out_put_disk:
while (dr--) {
del_timer_sync(&motor_off_timer[dr]);
- if (disks[dr]->queue)
+ if (disks[dr]->queue) {
blk_cleanup_queue(disks[dr]->queue);
+ /*
+ * put_disk() is not paired with add_disk() and
+ * will put queue reference one extra time. fix it.
+ */
+ disks[dr]->queue = NULL;
+ }
put_disk(disks[dr]);
}
return err;

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