[Linux-kernel-mentees] [PATCH net] Bluetooth: Fix slab-out-of-bounds read in hci_le_direct_adv_report_evt()

[Peilin Ye <yepeilin.cs@gmail.com>]

`num_reports` is not being properly checked. A malformed event packet with
a large `num_reports` number makes hci_le_direct_adv_report_evt() read out
of bounds. Fix it.

Reported-and-tested-by: syzbot+24ebd650e20bd263ca01@syzkaller.appspotmail.com
Fixes: 2f010b55884e ("Bluetooth: Add support for handling LE Direct Advertising Report events")
Link: https://syzkaller.appspot.com/bug?extid=24ebd650e20bd263ca01
Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
---
I moved the initialization of `ev` out of the loop and restructured the
function a bit, since otherwise the check would look like:

	if (!num_reports || skb->len < num_reports * sizeof(struct hci_ev_le_direct_adv_info) + 1)
		return;

Therefore I used the similar structure with hci_inquiry_result_evt() etc.

hci_le_adv_report_evt() and hci_le_ext_adv_report_evt() also have the
same issue with `num_reports`, but I'm not sure how to perform the check
for them, since they use variable-length reports. Should we do something
like this? (take hci_le_adv_report_evt() as example:)

	if (!num_reports ||
	    skb->len < num_reports * (sizeof(*ev) + HCI_MAX_AD_LENGTH + 1) + 1)
		return;

Then how about hci_le_ext_adv_report_evt()? There is no such
`HCI_MAX_AD_LENGTH` restrictions on `ev->length` for it, I assume?

Would like to hear your opinion. Thank you!

 net/bluetooth/hci_event.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index 4b7fc430793c..aec43ae488d1 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -5863,21 +5863,19 @@ static void hci_le_direct_adv_report_evt(struct hci_dev *hdev,
 					 struct sk_buff *skb)
 {
 	u8 num_reports = skb->data[0];
-	void *ptr = &skb->data[1];
+	struct hci_ev_le_direct_adv_info *ev = (void *)&skb->data[1];
 
-	hci_dev_lock(hdev);
+	if (!num_reports || skb->len < num_reports * sizeof(*ev) + 1)
+		return;
 
-	while (num_reports--) {
-		struct hci_ev_le_direct_adv_info *ev = ptr;
+	hci_dev_lock(hdev);
 
+	for (; num_reports; num_reports--, ev++)
 		process_adv_report(hdev, ev->evt_type, &ev->bdaddr,
 				   ev->bdaddr_type, &ev->direct_addr,
 				   ev->direct_addr_type, ev->rssi, NULL, 0,
 				   false);
 
-		ptr += sizeof(*ev);
-	}
-
 	hci_dev_unlock(hdev);
 }
 
-- 
2.25.1