linux-kernel - Re: [PATCH] Bluetooth: purge unhandled skbs

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Date:	Thu, 14 Apr 2016 15:41:34 +0100
From:	Marcel Holtmann <marcel@...tmann.org>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	Jiri Slaby <jslaby@...e.cz>,
	Johan Hedberg <johan.hedberg@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Gustavo F. Padovan" <gustavo@...ovan.org>,
	linux-bluetooth@...r.kernel.org,
	"stable 3 . 13+" <stable@...r.kernel.org>
Subject: Re: [PATCH] Bluetooth: purge unhandled skbs

Hi Takashi,

>>> The write handler allocates skbs and queues them into data->readq.
>>> Read side should read them, if there is any. If there is none, skbs
>>> should be dropped by hdev->flush. But this happens only if the device
>>> is HCI_UP, i.e. hdev->power_on work was triggered already. When it was
>>> not, skbs stay allocated in the queue when /dev/vhci is closed. So
>>> purge the queue in ->release.
>>> 
>>> Program to reproduce:
>>> 	#include <err.h>
>>> 	#include <fcntl.h>
>>> 	#include <stdio.h>
>>> 	#include <unistd.h>
>>> 
>>> 	#include <sys/stat.h>
>>> 	#include <sys/types.h>
>>> 	#include <sys/uio.h>
>>> 
>>> 	int main()
>>> 	{
>>> 		char buf[] = { 0xff, 0 };
>>> 		struct iovec iov = {
>>> 			.iov_base = buf,
>>> 			.iov_len = sizeof(buf),
>>> 		};
>>> 		int fd;
>>> 
>>> 		while (1) {
>>> 			fd = open("/dev/vhci", O_RDWR);
>>> 			if (fd < 0)
>>> 				err(1, "open");
>>> 
>>> 			usleep(50);
>>> 
>>> 			if (writev(fd, &iov, 1) < 0)
>>> 				err(1, "writev");
>>> 
>>> 			usleep(50);
>>> 
>>> 			close(fd);
>>> 		}
>>> 
>>> 		return 0;
>>> 	}
>>> 
>>> Result:
>>> kmemleak: 4609 new suspected memory leaks
>>> unreferenced object 0xffff88059f4d5440 (size 232):
>>> comm "vhci", pid 1084, jiffies 4294912542 (age 37569.296s)
>>> hex dump (first 32 bytes):
>>>   20 f0 23 87 05 88 ff ff 20 f0 23 87 05 88 ff ff   .#..... .#.....
>>>   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>>> backtrace:
>>> ...
>>>   [<ffffffff81ece010>] __alloc_skb+0x0/0x5a0
>>>   [<ffffffffa021886c>] vhci_create_device+0x5c/0x580 [hci_vhci]
>>>   [<ffffffffa0219436>] vhci_write+0x306/0x4c8 [hci_vhci]
>>> 
>>> Fixes: 23424c0d31 (Bluetooth: Add support creating virtual AMP controllers)
>>> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
>>> Cc: Marcel Holtmann <marcel@...tmann.org>
>>> Cc: Gustavo Padovan <gustavo@...ovan.org>
>>> Cc: Johan Hedberg <johan.hedberg@...il.com>
>>> Cc: <linux-bluetooth@...r.kernel.org>
>>> Cc: stable 3.13+ <stable@...r.kernel.org>
>>> ---
>>> drivers/bluetooth/hci_vhci.c | 1 +
>>> 1 file changed, 1 insertion(+)
>> 
>> patch has been applied to bluetooth-next tree.
> 
> Could you check another race of vhci mentioned in the thread?
>  https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1106134.html
> 
> If the suggested fix is OK, I'll submit a properly cooked patch.

lets get the patch send to the mailing list and then I can have a look at it. I might need to test the final patch so that it works with legacy userspace.

Regards

Marcel