Re: [PATCH] HID: elo: Fix refcount leak in elo_probe()

[Dan Carpenter <dan.carpenter@oracle.com>]

On Mon, Feb 14, 2022 at 09:41:32AM -0500, Alan Stern wrote:
> On Mon, Feb 14, 2022 at 03:34:42PM +0800, Dongliang Mu wrote:
> > On Sat, Feb 12, 2022 at 9:50 AM Alan Stern <stern@rowland.harvard.edu> wrote:
> > >
> > > Syzbot identified a refcount leak in the hid-elo driver:
> > >
> > > BUG: memory leak
> > > unreferenced object 0xffff88810d49e800 (size 2048):
> > >   comm "kworker/1:1", pid 25, jiffies 4294954629 (age 16.460s)
> > >   hex dump (first 32 bytes):
> > >     ff ff ff ff 31 00 00 00 00 00 00 00 00 00 00 00  ....1...........
> > >     00 00 00 00 00 00 00 00 00 00 00 00 03 00 00 00  ................
> > >   backtrace:
> > >     [<ffffffff82c87a62>] kmalloc include/linux/slab.h:581 [inline]
> > >     [<ffffffff82c87a62>] kzalloc include/linux/slab.h:715 [inline]
> > >     [<ffffffff82c87a62>] usb_alloc_dev+0x32/0x450 drivers/usb/core/usb.c:582
> > >     [<ffffffff82c91a47>] hub_port_connect drivers/usb/core/hub.c:5260 [inline]
> > >     [<ffffffff82c91a47>] hub_port_connect_change drivers/usb/core/hub.c:5502 [inline]
> > >     [<ffffffff82c91a47>] port_event drivers/usb/core/hub.c:5660 [inline]
> > >     [<ffffffff82c91a47>] hub_event+0x1097/0x21a0 drivers/usb/core/hub.c:5742
> > >     [<ffffffff8126c3ef>] process_one_work+0x2bf/0x600 kernel/workqueue.c:2307
> > >     [<ffffffff8126ccd9>] worker_thread+0x59/0x5b0 kernel/workqueue.c:2454
> > >     [<ffffffff81276765>] kthread+0x125/0x160 kernel/kthread.c:377
> > >     [<ffffffff810022ff>] ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
> > >
> > > Not shown in the bug report but present in the console log:
> > >
> > > [  182.014764][ T3257] elo 0003:04E7:0030.0006: item fetching failed at offset 0/1
> > > [  182.022255][ T3257] elo 0003:04E7:0030.0006: parse failed
> > > [  182.027904][ T3257] elo: probe of 0003:04E7:0030.0006 failed with error -22
> > > [  182.214767][ T3257] usb 1-1: USB disconnect, device number 7
> > > [  188.090199][ T3604] kmemleak: 3 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
> > > BUG: memory leak
> > >
> > > which points to hid-elo as the buggy driver.
> > >
> > > The leak is caused by elo_probe() failing to release the reference it
> > > holds to the struct usb_device in its failure pathway.  In the end the
> > > driver doesn't need to take this reference at all, because the
> > 
> > Hi Alan,
> > 
> > My patch "[PATCH] hid: elo: fix memory leak in elo_probe" is merged
> > several weeks ago.
> 
> Really?  It still isn't in Linus's tree as of 5.17-rc4.  I would expect 
> a bug fix to go upstream as soon as possible.
> 
> > However, I fix this bug by modifying the error handling code in
> > elo_probe. If you think the refcount is not necessary, maybe a new
> > patch to remove the refcount is better.
> 
> The refcount was added less than a year ago by Salah Triki in commit 
> fbf42729d0e9 ("HID: elo: update the reference count of the usb device 
> structure"), but the commit message doesn't explain why it is 
> necessary.  There certainly isn't any obvious reason for it; the driver 
> doesn't release any references after elo_remove() returns and we know 
> that the usb_device structure won't be deallocated before the driver 
> gets unbound.

Salah sent a bunch of these.  The reasoning was explained in this email.

https://www.spinics.net/lists/kernel/msg4026672.html

When he resent the patch, Greg said that taking the reference wasn't
needed so the patch wasn't applied.  (Also it had the same reference
leak so that's a second reason it wasn't applied).

https://lkml.org/lkml/2021/8/4/324

So someone should go through and revert all of Salah's bogus usb_get_dev()
patches.

regards,
dan carpenter