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Foster Snowhill says: ==================== usbnet: ipheth: prevent OoB reads of NDP16 iOS devices support two types of tethering over USB: regular, where the internet connection is shared from the phone to the attached computer, and reverse, where the internet connection is shared from the attached computer to the phone. The `ipheth` driver is responsible for regular tethering only. With this tethering type, iOS devices support two encapsulation modes on RX: legacy and NCM. In "NCM mode", the iOS device encapsulates RX (phone->computer) traffic in NCM Transfer Blocks (similarly to CDC NCM). However, unlike reverse tethering, regular tethering is not compliant with the CDC NCM spec: * Does not have the required CDC NCM descriptors * TX (computer->phone) is not NCM-encapsulated at all Thus `ipheth` implements a very limited subset of the spec with the sole purpose of parsing RX URBs. This driver does not aim to be a CDC NCM-compliant implementation and, in fact, can't be one because of the points above. For a complete spec-compliant CDC NCM implementation, there is already the `cdc_ncm` driver. This driver is used for reverse tethering on iOS devices. This patch series does not in any way change `cdc_ncm`. In the first iteration of the NCM mode implementation in `ipheth`, there were a few potential out of bounds reads when processing malformed URBs received from a connected device: * Only the start of NDP16 (wNdpIndex) was checked to fit in the URB buffer. * Datagram length check as part of DPEs could overflow. * DPEs could be read past the end of NDP16 and even end of URB buffer if a trailer DPE wasn't encountered. The above is not expected to happen in normal device operation. To address the above issues for iOS devices in NCM mode, rely on and check for a specific fixed format of incoming URBs expected from an iOS device: * 12-byte NTH16 * 96-byte NDP16, allowing up to 22 DPEs (up to 21 datagrams + trailer) On iOS, NDP16 directly follows NTH16, and its length is constant regardless of the DPE count. As the regular tethering implementation of iOS devices isn't compliant with CDC NCM, it's not possible to use the `cdc_ncm` driver to handle this functionality. Furthermore, while the logic required to properly parse URBs with NCM-encapsulated frames is already part of said driver, I haven't found a nice way to reuse the existing code without messing with the `cdc_ncm` driver itself. I didn't want to reimplement more of the spec than I absolutely had to, because that work had already been done in `cdc_ncm`. Instead, to limit the scope, I chose to rely on the specific URB format of iOS devices that hasn't changed since the NCM mode was introduced there. I tested each individual patch in the v5 series with iPhone 15 Pro Max, iOS 18.2.1: compiled cleanly, ran iperf3 between phone and computer, observed no errors in either kernel log or interface statistics. v4 was Reviewed-by Jakub Kicinski <kuba@kernel.org>. Compared to v4, v5 has no code changes. The two differences are: * Patch "usbnet: ipheth: break up NCM header size computation" moved later in the series, closer to a subsequent commit that makes use of the change. * In patch "usbnet: ipheth: refactor NCM datagram loop", removed a stray paragraph in commit msg. Above items are also noted in the changelogs of respective patches. ==================== Link: https://patch.msgid.link/20250125235409.3106594-1-forst@pen.gy Signed-off-by: Paolo Abeni <pabeni@redhat.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.