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

From: Dan Carpenter
Date: Sat Mar 30 2019 - 03:18:29 EST


[ 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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