On 2/10/22 16:54, Oliver Neukum wrote:
A broken device may give an extreme offset like 0xFFF0
and a reasonable length for a fragment. In the sanity
check as formulated now, this will create an integer
overflow, defeating the sanity check. It needs to be
rewritten as a subtraction and the variables should be
unsigned.
Hi Oliver,
First of all I'd like to update:
Hans Petter Selasky <hans.petter.selasky@xxxxxxxxxxxxxx>
To:
Hans Petter Selasky <hselasky@xxxxxxxxxxx>
Secondly,
"int" variables are 32-bit, so 0xFFF0 won't overflow.
The initial driver code written by me did only support 16-bit lengths
and offset. Then integer overflow is not possible.
It looks like somebody else introduced this integer overflow :-(
commit 0fa81b304a7973a499f844176ca031109487dd31
Author: Alexander Bersenev <bay@xxxxxxxxxxxx>
Date: Fri Mar 6 01:33:16 2020 +0500
cdc_ncm: Implement the 32-bit version of NCM Transfer Block
The NCM specification defines two formats of transfer blocks: with
16-bit
fields (NTB-16) and with 32-bit fields (NTB-32). Currently only
NTB-16 is
implemented.
....
With NCM 32, both "len" and "offset" must be checked, because these are
now 32-bit and stored into regular "int".
The fix you propose is not fully correct!
--HPS
Signed-off-by: Oliver Neukum <oneukum@xxxxxxxx>
---
drivers/net/usb/cdc_ncm.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
index e303b522efb5..f78fccbc4b93 100644
--- a/drivers/net/usb/cdc_ncm.c
+++ b/drivers/net/usb/cdc_ncm.c
@@ -1715,10 +1715,10 @@ int cdc_ncm_rx_fixup(struct usbnet *dev, struct sk_buff *skb_in)
{
struct sk_buff *skb;
struct cdc_ncm_ctx *ctx = (struct cdc_ncm_ctx *)dev->data[0];
- int len;
+ unsigned int len;
int nframes;
int x;
- int offset;
+ unsigned int offset;
union {
struct usb_cdc_ncm_ndp16 *ndp16;
struct usb_cdc_ncm_ndp32 *ndp32;
@@ -1791,7 +1791,7 @@ int cdc_ncm_rx_fixup(struct usbnet *dev, struct sk_buff *skb_in)
}
/* sanity checking */
- if (((offset + len) > skb_in->len) ||
+ if ((offset > skb_in->len - len) ||
(len > ctx->rx_max) || (len < ETH_HLEN)) {
netif_dbg(dev, rx_err, dev->net,
"invalid frame detected (ignored) offset[%u]=%u, length=%u, skb=%p\n",
