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From:   Anant Thazhemadam <anant.thazhemadam@gmail.com>
To:     linux-kernel-mentees@lists.linuxfoundation.org
Cc:     Anant Thazhemadam <anant.thazhemadam@gmail.com>,
        Marcel Holtmann <marcel@holtmann.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [Linux-kernel-mentees] [PATCH] Fix uninit-value in hci_chan_lookup_handle
Date:   Sat,  5 Sep 2020 07:34:10 +0530
Message-Id: <20200905020410.20350-1-anant.thazhemadam@gmail.com>
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Sender: linux-bluetooth-owner@vger.kernel.org
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When the amount of data stored in the location corresponding to
iov_iter *from is less then 4, some data seems to go uninitialized.

Updating this condition accordingly, makes sense both intuitively and 
logically as well, since the other check for extreme condition done is if
len > HCI_MAX_FRAME_SIZE, which is HCI_MAX_ACL_SIZE (which is 1024) + 4;
which itself gives some idea about what must be the ideal mininum size.

Reported-and-tested by: syzbot+4c14a8f574461e1c3659@syzkaller.appspotmail.com
Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
---
If there is some explicit reason why len < 4 doesn't work, and only len < 2 works, 
please do let me know.
The commit message that introduced the initial change 
(512b2268156a4e15ebf897f9a883bdee153a54b7) wasn't exactly very helpful in this 
respect, and I couldn't find a whole lot of discussion regarding this either.

 drivers/bluetooth/hci_vhci.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/bluetooth/hci_vhci.c b/drivers/bluetooth/hci_vhci.c
index 8ab26dec5f6e..0c49821d7b98 100644
--- a/drivers/bluetooth/hci_vhci.c
+++ b/drivers/bluetooth/hci_vhci.c
@@ -159,7 +159,7 @@ static inline ssize_t vhci_get_user(struct vhci_data *data,
 	__u8 pkt_type, opcode;
 	int ret;
 
-	if (len < 2 || len > HCI_MAX_FRAME_SIZE)
+	if (len < 4 || len > HCI_MAX_FRAME_SIZE)
 		return -EINVAL;
 
 	skb = bt_skb_alloc(len, GFP_KERNEL);
-- 
2.25.1