linux-kernel - Re: [PATCH] net/bluetooth: Fix bound check in event handling

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Message-ID: <20190330071757.GU32613@kadam>
Date:   Sat, 30 Mar 2019 10:17:57 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     kbuild@...org, Tomas Bortoli <tomasbortoli@...il.com>
Cc:     kbuild-all@...org, marcel@...tmann.org, johan.hedberg@...il.com,
        davem@...emloft.net, linux-bluetooth@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller@...glegroups.com, Tomas Bortoli <tomasbortoli@...il.com>
Subject: Re: [PATCH] net/bluetooth: Fix bound check in event handling

[ This is an old warning.  Sorry for missing it earlier.  I would have
  caught it when the code was merged as well so there was no real risk
  but it's just awkward.  ]

Hi Tomas,

url:    https://github.com/0day-ci/linux/commits/Tomas-Bortoli/net-bluetooth-Fix-bound-check-in-event-handling/20190301-213647
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next.git master

smatch warnings:
net/bluetooth/hci_event.c:3986 hci_inquiry_result_with_rssi_evt() warn: potential pointer math issue ('info' is a 120 bit pointer)

# https://github.com/0day-ci/linux/commit/00305742c021794f147b348d45eb10ea26e5a514
git remote add linux-review https://github.com/0day-ci/linux
git remote update linux-review
git checkout 00305742c021794f147b348d45eb10ea26e5a514
vim +3986 net/bluetooth/hci_event.c

6039aa73 Gustavo Padovan 2012-05-23  3963  static void hci_inquiry_result_with_rssi_evt(struct hci_dev *hdev,
807deac2 Gustavo Padovan 2012-05-17  3964  					     struct sk_buff *skb)
a9de9248 Marcel Holtmann 2007-10-20  3965  {
a9de9248 Marcel Holtmann 2007-10-20  3966  	struct inquiry_data data;
a9de9248 Marcel Holtmann 2007-10-20  3967  	int num_rsp = *((__u8 *) skb->data);
a9de9248 Marcel Holtmann 2007-10-20  3968  
a9de9248 Marcel Holtmann 2007-10-20  3969  	BT_DBG("%s num_rsp %d", hdev->name, num_rsp);
a9de9248 Marcel Holtmann 2007-10-20  3970  
a9de9248 Marcel Holtmann 2007-10-20  3971  	if (!num_rsp)
a9de9248 Marcel Holtmann 2007-10-20  3972  		return;
a9de9248 Marcel Holtmann 2007-10-20  3973  
d7a5a11d Marcel Holtmann 2015-03-13  3974  	if (hci_dev_test_flag(hdev, HCI_PERIODIC_INQ))
1519cc17 Andre Guedes    2012-03-21  3975  		return;
1519cc17 Andre Guedes    2012-03-21  3976  
a9de9248 Marcel Holtmann 2007-10-20  3977  	hci_dev_lock(hdev);
a9de9248 Marcel Holtmann 2007-10-20  3978  
a9de9248 Marcel Holtmann 2007-10-20  3979  	if ((skb->len - 1) / num_rsp != sizeof(struct inquiry_info_with_rssi)) {
138d22ef Szymon Janc     2011-02-17  3980  		struct inquiry_info_with_rssi_and_pscan_mode *info;
138d22ef Szymon Janc     2011-02-17  3981  		info = (void *) (skb->data + 1);
a9de9248 Marcel Holtmann 2007-10-20  3982  
e17acd40 Johan Hedberg   2011-03-30  3983  		for (; num_rsp; num_rsp--, info++) {
af58925c Marcel Holtmann 2014-07-01  3984  			u32 flags;
af58925c Marcel Holtmann 2014-07-01  3985  
00305742 Tomas Bortoli   2019-02-28 @3986  			if ((void *)(info + sizeof(info)) >
                                                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This should be (void *)info + sizeof(info).  The code you have will
break for valid uses because the pointer math error.  I notice that
this isn't merged into linux-next, but it does seem required.  I am
writing a similar fix for a different function.

Another way to write this would be:

		if ((u8 *)(info + 1) > &skb->data[skb->len]) {


00305742 Tomas Bortoli   2019-02-28  3987  			   (void *)(skb->data + skb->len))
00305742 Tomas Bortoli   2019-02-28  3988  				break;
00305742 Tomas Bortoli   2019-02-28  3989  
a9de9248 Marcel Holtmann 2007-10-20  3990  			bacpy(&data.bdaddr, &info->bdaddr);
a9de9248 Marcel Holtmann 2007-10-20  3991  			data.pscan_rep_mode	= info->pscan_rep_mode;
a9de9248 Marcel Holtmann 2007-10-20  3992  			data.pscan_period_mode	= info->pscan_period_mode;
a9de9248 Marcel Holtmann 2007-10-20  3993  			data.pscan_mode		= info->pscan_mode;
a9de9248 Marcel Holtmann 2007-10-20  3994  			memcpy(data.dev_class, info->dev_class, 3);
a9de9248 Marcel Holtmann 2007-10-20  3995  			data.clock_offset	= info->clock_offset;
a9de9248 Marcel Holtmann 2007-10-20  3996  			data.rssi		= info->rssi;
41a96212 Marcel Holtmann 2008-07-14  3997  			data.ssp_mode		= 0x00;
3175405b Johan Hedberg   2012-01-04  3998  
af58925c Marcel Holtmann 2014-07-01  3999  			flags = hci_inquiry_cache_update(hdev, &data, false);
af58925c Marcel Holtmann 2014-07-01  4000  
48264f06 Johan Hedberg   2011-11-09  4001  			mgmt_device_found(hdev, &info->bdaddr, ACL_LINK, 0x00,
e17acd40 Johan Hedberg   2011-03-30  4002  					  info->dev_class, info->rssi,
af58925c Marcel Holtmann 2014-07-01  4003  					  flags, NULL, 0, NULL, 0);
a9de9248 Marcel Holtmann 2007-10-20  4004  		}
a9de9248 Marcel Holtmann 2007-10-20  4005  	} else {

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