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Message-ID: <PH0PR21MB3025F31739A0480F66639ACAD7EE9@PH0PR21MB3025.namprd21.prod.outlook.com> Date: Fri, 15 Apr 2022 14:27:37 +0000 From: "Michael Kelley (LINUX)" <mikelley@...rosoft.com> To: Andrea Parri <parri.andrea@...il.com> CC: KY Srinivasan <kys@...rosoft.com>, Haiyang Zhang <haiyangz@...rosoft.com>, Stephen Hemminger <sthemmin@...rosoft.com>, Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>, Stefano Garzarella <sgarzare@...hat.com>, David Miller <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>, "virtualization@...ts.linux-foundation.org" <virtualization@...ts.linux-foundation.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: RE: [RFC PATCH 1/6] hv_sock: Check hv_pkt_iter_first_raw()'s return value From: Andrea Parri <parri.andrea@...il.com> Sent: Thursday, April 14, 2022 11:42 PM > > On Fri, Apr 15, 2022 at 03:33:23AM +0000, Michael Kelley (LINUX) wrote: > > From: Andrea Parri (Microsoft) <parri.andrea@...il.com> Sent: Wednesday, April 13, > 2022 1:48 PM > > > > > > The function returns NULL if the ring buffer has no enough space > > > available for a packet descriptor. The ring buffer's write_index > > > > The first sentence wording is a bit scrambled. I think you mean the > > ring buffer doesn't contain enough readable bytes to constitute a > > packet descriptor. > > Indeed, replaced with your working. > > > > > is in memory which is shared with the Hyper-V host, its value is > > > thus subject to being changed at any time. > > > > This second sentence is true, but I'm not making the connection > > with the code change below. Evidently, there is some previous > > check made to ensure that enough bytes are available to be > > received when hvs_stream_dequeue() is called, so we assumed that > > NULL could never be returned? I looked but didn't find such a check, > > so maybe I didn't look carefully enough. But now we are assuming > > that Hyper-V might have invalidated that previous check by > > subsequently changing the write_index in a bogus way? So now, NULL > > could be returned when previously we assumed it couldn't. > > I think you're looking for hvs_stream_has_data(). (Previous checks > apart, hvs_stream_dequeue() will "dereference" the pointer so...) Agreed. I didn't say this explicitly, but I was wondering about the risk in the current code (without these hardening patches) of getting a NULL pointer from hv_pkt_iter_first_raw(), and then dereferencing it. Michael
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