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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Op1czpXG/VkE4BR4++qVQNjZiLSQTMRo6R7AHTASdP0=; b=QKp3FTQaegblQKhj+tNEs9Emknow0scSGj6eEdcT6g65zs6XN3rp9ElIKkBCZPfjuf pXzfLOdGUjIZZsJubcbo42jtDUw66u6ZCtQ9OFMqSk6OZuPwHO1JfufnjUYrzcb9mB2r N3rgBPQqN4BuOTbmk9DZNgt7BTF2EGEqa8bwJ1YiA/LHz6NL/6JuqbT6S/QDPv4dM4+5 litV6ViTGR7nCU1IMCdVuUlX52yU4qQWjJPtrNqo3dby4YQT9qh3RBEgshnRmJO1eKXb gUqwl2Y3t+tD54KHtE1ylay6vgBowsHL/D1Fi8qr6Pceqh6Ia9TNMr5MmWbPobXwWwgw n9dQ== X-Gm-Message-State: AOAM5321PhObwStH1ZiyLM/RoZgDDaKiMIkF5s0Ejf032JfCp0xo7qAH NOHf8cClDzN+2I9YZs4afCrGhH5k//NWg2ZYt5DmKARmi78= X-Google-Smtp-Source: ABdhPJx49Lc4wyd7DIxK2LmZzqUThk8AWhOM212xm0BTV8n65kH62iatnkAnJlP8eZEjwFyO+R3wW0JiwZutori/AEw= X-Received: by 2002:ac8:480c:: with SMTP id g12mr26079296qtq.257.1597054920691; Mon, 10 Aug 2020 03:22:00 -0700 (PDT) MIME-Version: 1.0 References: <000000000000ce85c405ac744ff6@google.com> <20200810074706.GD1529187@kroah.com> <20200810090833.GA2271719@kroah.com> <20200810091538.GA2273701@kroah.com> <20200810095754.GA2404978@kroah.com> In-Reply-To: <20200810095754.GA2404978@kroah.com> From: Dmitry Vyukov Date: Mon, 10 Aug 2020 12:21:49 +0200 Message-ID: Subject: Re: KMSAN: kernel-infoleak in raw_ioctl To: Greg KH Cc: syzbot , Andrey Konovalov , balbi@kernel.org, Dan Carpenter , Alexander Potapenko , LKML , USB list , syzkaller-bugs Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 10, 2020 at 11:57 AM Greg KH wrote: > > On Mon, Aug 10, 2020 at 11:15:38AM +0200, Greg KH wrote: > > On Mon, Aug 10, 2020 at 11:08:33AM +0200, Greg KH wrote: > > > On Mon, Aug 10, 2020 at 11:00:07AM +0200, Dmitry Vyukov wrote: > > > > On Mon, Aug 10, 2020 at 9:46 AM Greg KH wrote: > > > > > > > > > > On Sun, Aug 09, 2020 at 09:27:18AM -0700, syzbot wrote: > > > > > > Hello, > > > > > > > > > > > > syzbot found the following issue on: > > > > > > > > > > > > HEAD commit: ce8056d1 wip: changed copy_from_user where instrumented > > > > > > git tree: https://github.com/google/kmsan.git master > > > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=141eb8b2900000 > > > > > > kernel config: https://syzkaller.appspot.com/x/.config?x=3afe005fb99591f > > > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=a7e220df5a81d1ab400e > > > > > > compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81) > > > > > > userspace arch: i386 > > > > > > > > > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > > > > > > > The irony of a kernel module written for syzbot testing, causing syzbot > > > > > reports.... > > > > > > > > The raw gadget and KCOV are also kernel code and subject to all the > > > > same rules as any other kernel code from syzkaller point of view. > > > > > > > > But I think the root cause of this bug is the origin of the uninitialized-ness: > > > > > > > > Local variable ----buf.i@asix_get_phy_addr created at: > > > > asix_read_cmd drivers/net/usb/asix_common.c:312 [inline] > > > > asix_read_phy_addr drivers/net/usb/asix_common.c:295 [inline] > > > > asix_get_phy_addr+0x4d/0x290 drivers/net/usb/asix_common.c:314 > > > > asix_read_cmd drivers/net/usb/asix_common.c:312 [inline] > > > > asix_read_phy_addr drivers/net/usb/asix_common.c:295 [inline] > > > > asix_get_phy_addr+0x4d/0x290 drivers/net/usb/asix_common.c:314 > > > > > > read buffers sent to USB hardware are ment to be filled in by the > > > hardware with the data received from it, we do not zero-out those > > > buffers before passing the pointer there. > > > > > > Perhaps with testing frameworks like the raw usb controller, that might > > > cause a number of false-positives to happen? > > > > Ah, wait, that buffer is coming from the stack, which isn't allowed in > > the first place :( > > > > So that should be changed anyway to a dynamic allocation, I'll go write > > up a patch... > > Nope, my fault, the data is not coming from the stack, so all is good. My reading of the code is that asix_read_cmd returns the number of bytes actually read, which may be less than requested. This happens in __usbnet_read_cmd: https://elixir.bootlin.com/linux/latest/source/drivers/net/usb/usbnet.c#L2002 So this code in asix_read_phy_addr will need produce an uninit value for result if <2 bytes read: u8 buf[2]; int ret = asix_read_cmd(dev, AX_CMD_READ_PHY_ID, 0, 0, 2, buf, 0); if (ret < 0) netdev_err(dev->net, "Error reading PHYID register: %02x\n", ret); ret = buf[offset]; return ret; And it looks like all of 13 uses of asix_read_cmd in drivers/net/usb/asix_common.c are subject to this bug as well.