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 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 :) > Thank you! > Atul With regards, Pavel Skripkin
