Would it be possible for you to test the latest upstream stable kernel? Refer to https://wiki.ubuntu.com/KernelMainlineBuilds . Please test the latest v4.4 stable kernel[0].
If this bug is fixed in the mainline kernel, please add the following tag 'kernel-fixed-upstream'. If the mainline kernel does not fix this bug, please add the tag: 'kernel-bug-exists-upstream'. If you are unable to test the mainline kernel, for example it will not boot, please add the tag: 'kernel-unable-to-test-upstream'. Once testing of the upstream kernel is complete, please mark this bug as "Confirmed". Thanks in advance. [0] http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.4.145 ** Changed in: linux (Ubuntu) Importance: Undecided => High ** Information type changed from Public to Private Security ** Tags added: kernel-key -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1784684 Title: Waste padding after PPPoE payload Status in linux package in Ubuntu: Confirmed Bug description: After a new Kernel e.g. 4.4.0-131 is installed on our Ubuntu 16.04 LTS clients, unneeded (waste) 14 bytes paddings are unexpectedly present after PPPoE payload in client's Ethernet frames which are sent towards a NAS access router. The content of such a waste padding is not all zero filled bytes, but rather parts of memory, sometimes with readable text. Thus it is also a security issue. Sometimes the waste padding is more than 14 bytes. For example, a PPPoED PADI frame (single tagged VLAN) with text "amf/application/12" (18 bytes) at the end of the frame shown as padding in Wireshark: 0000 ff ff ff ff ff ff 00 0a cd 2a ea 9f 81 00 00 07 ÿÿÿÿÿÿ..Í*ê..... 0010 88 63 11 09 00 00 00 0c 01 01 00 00 01 03 00 04 .c.............. 0020 d9 1f 00 00 61 6d 66 2f 61 70 70 6c 69 63 61 74 Ù...amf/applicat 0030 69 6f 6e 2f 31 32 ion/12 It is a critical bug of Kernel 4.4.0-131. Some affected client Ethernet frames are large enough (>64 bytes), and thus they do not need to be padded for Ethernet. Padding should be included and is required in Ethernet frames only to achieve the minimum 64 byte size of an Ethernet frame sent on wire. For a packet larger than e.g. 100 bytes no padding is needed in Ethernet frame. However we can see such 14 Byte paddings also in large client Ethernet frames (in PPPoE/PPP/IP session packets), with payload size of several hundred bytes (200, 300, 400 bytes and more). Our Ubuntu 16.04 LTS Clients are always updated via apt update / apt upgrade early enough, after a new Ubuntu update is released in Internet. Our statistics after analyzing the collected archived pcap traces of our clients with Ubuntu 16.04 LTS and the latest Kernel installed can help to identify the date and the version when the kernel bug first appeared: From 15.06.2018 to 29.06.2018 - still no waste padding on all clients (OK) 02.07.2018 - OK, still no waste padding on all clients (OK) 03.07.2018 - OK, still no waste padding on all clients (OK) 04.07.2018 - OK, still no waste padding on all clients (OK) 05.07.2018 - OK, still no waste padding on all clients (OK) 06.07.2018 - OK, still no waste padding on all clients (OK) !!! Kernel Update to 4.4.0-131 on 09-Jul-2018 !!! 09.07.2018 - 14 byte padding (PADI, PADR, etc) on all updated clients - a kernel BUG ! 10.07.2018 - 14 byte padding (PADI, PADR, etc) on all updated clients - a kernel BUG ! 12.07.2018 - 14 byte padding (PADI, PADR, etc) on all updated clients - a kernel BUG ! 13.07.2018 - 14 byte padding (PADI, PADR, etc) on all updated clients - a kernel BUG ! 19.07.2018 - 14 byte padding (PADI, PADR, etc) on all updated clients - a kernel BUG ! ... So the padding issue occurred on our Ubuntu 16.04 LTS clients for the first time on 09-Jul-2018, after the Linux Kernel was updated to 4.4.0-131. Since then, the issue is present on all the updated clients. The kernel bug disappeared and the padding behavior is OK again (without bug), after clients were downgraded to and booted with an older kernel version like e.g. 4.4.0-116 (older than 4.4.0-131). Information about the Ubuntu clients and the kernel version affected with this BUG: @client:~$ uname -a Linux client 4.4.0-131-generic #157-Ubuntu SMP Thu Jul 12 15:51:36 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux @client:~$ cat /proc/version_signature Ubuntu 4.4.0-131.157-generic 4.4.134 @client:~$ lsb_release -rd Description: Ubuntu 16.04.5 LTS Release: 16.04 @client:~$ lsb_release -ci Distributor ID: Ubuntu Codename: xenial The kernel bug does not occur and waste paddings (14 byte on single- stacked VLAN, 18 byte on double-stacked VLAN) are not present in client frames, if an old Kernel e.g. 4.4.0-116 (of 12-Feb-2018) is installed on the client and activated at boot time. This old kernel 4.4.0-116 is still without the padding bug: @client:~$ uname -a Linux client 4.4.0-116-generic #140-Ubuntu SMP Mon Feb 12 21:23:04 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux A PADI packet with unneeded padding is included as attachment. It was captured via tcpdump directly on the Ubuntu Client. It is a padding inserted by Ubuntu, not by the HW or driver. If it were a padding included by Ethernet adapter or driver to reach the minimum 64 byte frame size, we could not capture such real padding on the WAN interface of the same host and could not see such real padding of this client frame in Wireshark. The issue affects PPPoED client packets (PADI, PADR), PPP control client packets (e.g. LCP) and PPP session client packets (IPv4 / IPv6). We expect no padding is included after PPPoE payload in Ethernet frames if the packets are not small (>64 byte) and thus are not required to be padded for Ethernet. Such correct behavior (without waste paddings) can be observed on Ubuntu 16.04 LTS with old Kernel versions (like e.g. 4.4.0-116) released before July 2018. Please implement the fix in the next Kernel update. 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