[PATCH] Bluetooth: add timeout sanity check to hci_inquiry

[Pavel Skripkin <paskripkin@gmail.com>]

Syzbot hit "task hung" bug in hci_req_sync(). The problem was in
unreasonable huge inquiry timeout passed from userspace.
Fix it by adding sanity check for timeout value and add constant to
hsi_sock.h to inform userspace, that hci_inquiry_req::length field has
maximum possible value.

Since hci_inquiry() is the only user of hci_req_sync() with user
controlled timeout value, it makes sense to check timeout value in
hci_inquiry() and don't touch hci_req_sync().

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-and-tested-by: syzbot+be2baed593ea56c6a84c@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
---

Hi, Bluetooth maintainers/reviewers!

I believe, 60 seconds will be more than enough for inquiry request. I've
searched for examples on the internet and maximum ir.length I found was 
8. Maybe, we have users, which need more than 60 seconds... I look forward
to receiving your views on this value.

---
 include/net/bluetooth/hci_sock.h | 1 +
 net/bluetooth/hci_core.c         | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/include/net/bluetooth/hci_sock.h b/include/net/bluetooth/hci_sock.h
index 9949870f7d78..1cd63d4da00b 100644
--- a/include/net/bluetooth/hci_sock.h
+++ b/include/net/bluetooth/hci_sock.h
@@ -168,6 +168,7 @@ struct hci_inquiry_req {
 	__u16 dev_id;
 	__u16 flags;
 	__u8  lap[3];
+#define HCI_INQUIRY_MAX_TIMEOUT		30
 	__u8  length;
 	__u8  num_rsp;
 };
diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index e1a545c8a69f..104babf67351 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -1343,6 +1343,11 @@ int hci_inquiry(void __user *arg)
 		goto done;
 	}
 
+	if (ir.length > HCI_INQUIRY_MAX_TIMEOUT) {
+		err = -EINVAL;
+		goto done;
+	}
+
 	hci_dev_lock(hdev);
 	if (inquiry_cache_age(hdev) > INQUIRY_CACHE_AGE_MAX ||
 	    inquiry_cache_empty(hdev) || ir.flags & IREQ_CACHE_FLUSH) {
-- 
2.32.0