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    SubjectRe: Memory leak in ath9k_hif_usb_dealloc_tx_urbs()
    On Tue, Apr 27, 2021 at 03:29:28PM +0300, Pavel Skripkin wrote:
    > On Tue, 27 Apr 2021 15:04:29 +0300
    > Pavel Skripkin <paskripkin@gmail.com> wrote:
    >
    > > Hi!
    > >
    > > On Tue, 2021-04-27 at 17:05 +0530, Atul Gopinathan wrote:
    > > > On Wed, Mar 31, 2021 at 08:28:15AM +0200, Greg KH wrote:
    > > > > On Tue, Mar 30, 2021 at 10:36:52PM +0300, Pavel Skripkin wrote:
    > > > > > Hi!
    > > > > >
    > > > > > I did some debugging on this
    > > > > > https://syzkaller.appspot.com/bug?id=3ea507fb3c47426497b52bd82b8ef0dd5b6cc7ee
    > > > > > and, I believe, I recognized the problem. The problem appears in
    > > > > > case of
    > > > > > ath9k_htc_hw_init() fail. In case of this fail all tx_buf->urb
    > > > > > krefs will be
    > > > > > initialized to 1, but in free function:
    > > > > >
    > > > > > static void ath9k_hif_usb_dealloc_tx_urbs(struct hif_device_usb
    > > > > > *hif_dev)
    > > > > >
    > > > > > ....
    > > > > >
    > > > > > static void ath9k_hif_usb_dealloc_tx_urbs(struct hif_device_usb
    > > > > > *hif_dev)
    > > > > > {
    > > > > >     ...
    > > > > >         list_for_each_entry_safe(tx_buf, tx_buf_tmp,
    > > > > >                                  &hif_dev->tx.tx_buf, list) {
    > > > > >                 usb_get_urb(tx_buf->urb);
    > > > > >                 ...
    > > > > >                 usb_free_urb(tx_buf->urb);
    > > > > >                 ...
    > > > > >                 }
    > > > > >
    > > > > > Krefs are incremented and then decremented, that means urbs
    > > > > > won't be freed.
    > > > > > I found your patch and I can't properly understand why You added
    > > > > > usb_get_urb(tx_buf->urb).
    > > > > > Can You explain please, I believe this will help me or somebody
    > > > > > to fix this ussue :)
    > > > >
    > > > > I think almost everyone who has looked into this has given up due
    > > > > to the
    > > > > mess of twisty-passages here with almost no real-world benefits
    > > > > for unwinding them :)
    > > >
    > > > Just wanted to confirm, what is the status of this bug then, as in
    > > > is it
    > > > invalid (not sure if that's the correct word)? I happened to stumble
    > > > across the same syzkaller bug report Pavel posted above, in the
    > > > morning.
    > > > Saw that there has been no patch tests/fixes on this yet according
    > > > to syzkaller. Spent a couple of hours going through it before
    > > > sending a test patch to syzbot which returned an "OK" (and the
    > > > patch is exactly what Pavel pointed out, I simply removed the
    > > > `usb_get_urb()`). Before sending anything to the mailing list, I
    > > > made sure to search all the relavant networking lists to see if
    > > > this topic had been brought up (learnt
    > > > to do this from my preious mistakes of sending already accepted
    > > > patches) and
    > > > luckily I found this.
    > > >
    > > > Syzbot has had 380 crashes caused by this bug, with the latest being
    > > > today. So I wanted to confirm what should be done be about this
    > > > bug.
    > > >
    > >
    > > I saw on dashboard, that Dmitry tested latest upstream commit and
    > > syzbot returned "OK", but usb_get_urb(tx_buf->urb); is still there.
    > >
    >
    > I am sorry, I clicked wrong link on dashboard :( My bad.

    Oh right, I forgot to mention. Just want to make it clear that the test
    patch was mine. There was a bug in syzkaller, so when I sent the patches
    for testing they returned a weird error. Dmitry later pointed out that
    it was a syzkaller bug and was kind enough to re-send my patch on a
    fixed commit of syzkaller.

    https://groups.google.com/g/syzkaller-bugs/c/cBQP4fKjhFQ

    >
    > I believe, You can test your patch on this
    > https://syzkaller.appspot.com/bug?id=cabffad18eb74197f84871802fd2c5117b61febf.
    >
    > usb_get_urb(tx_buf->urb) was introduced in patch related to this bug
    >
    > > I think, this usb_get_urb prevents race condition, but I'm not sure
    > > about it, that's why I sent an email to patch author. As You can see,
    > > he has not responded yet :)

    Ah that's how it is. Well not sure we could do much here. Also thanks
    for clarifying things, I thought that no one had been looking into this
    bug especially when it had so many crash counts which suprised me, but I
    guess I was wrong.

    Thank you!
    Atul

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