Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH 1/4] ozwpan: Use proper check to prevent heap overflow | Date | Fri, 15 May 2015 15:02:07 +0000 |
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From: Jason A. Donenfeld > Sent: 13 May 2015 19:34 > Since elt->length is a u8, we can make this variable a u8. Then we can > do proper bounds checking more easily. Without this, a potentially > negative value is passed to the memcpy inside oz_hcd_get_desc_cnf, > resulting in a remotely exploitable heap overflow with network > supplied data. ... > diff --git a/drivers/staging/ozwpan/ozusbsvc1.c b/drivers/staging/ozwpan/ozusbsvc1.c > index d434d8c..cd6c63e 100644 > --- a/drivers/staging/ozwpan/ozusbsvc1.c > +++ b/drivers/staging/ozwpan/ozusbsvc1.c > @@ -390,8 +390,10 @@ void oz_usb_rx(struct oz_pd *pd, struct oz_elt *elt) > case OZ_GET_DESC_RSP: { > struct oz_get_desc_rsp *body = > (struct oz_get_desc_rsp *)usb_hdr; > - int data_len = elt->length - > + u8 data_len = elt->length - > sizeof(struct oz_get_desc_rsp) + 1; > + if (data_len > elt->length) > + break;
Why not just check the length. eg: unsigned int data_len = elt->length; if (data_len < sizeof(struct oz_get_desc_rsp) + 1) break;
> u16 offs = le16_to_cpu(get_unaligned(&body->offset)); > u16 total_size = > le16_to_cpu(get_unaligned(&body->total_size));
Don't put variable definitions after code.
You don't really want to do arithmetic on local variables that are smaller than a machine word (eg u8 and u16), doing so can require the compiler generate a lot more code.
David
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