Re: [PATCH] net/bluetooth: Fix bound check in event handling
From: Tomas Bortoli <hidden>
Date: 2019-03-30 22:37:26
Also in:
linux-bluetooth, lkml
Hi Dan, On 3/30/19 8:17 AM, Dan Carpenter wrote:
[ 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]) {
Yeah it hasn't been accepted afaik. Why just + 1 ? Also, &skb->data[skb->len] is right after the last byte so the > should rather be a >=, I think. your code looks better (as per pointer casting) but is logically different from what I proposed with v2: https://lkml.org/lkml/2019/3/4/892 I think the bound check should validate that there is enough data from the info pointer to read an entire struct inquiry_info_with_rssi_and_pscan_mode. Best regards, Tomas