> On Jan 9, 2023, at 03:42, Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx> wrote: > > On 09/01/2023 09:14, Krzysztof Kozlowski wrote: >> On 08/01/2023 18:09, Trond Myklebust wrote: >>> Hi Krzysztof, >>> >>>> On Jan 8, 2023, at 08:25, Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx> wrote: >>>> >>>> [You don't often get email from krzysztof.kozlowski@xxxxxxxxxx. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification] >>>> >>>> On 07/01/2023 16:44, Krzysztof Kozlowski wrote: >>>>> Hi, >>>>> >>>>> Bisect identified commit 7fd461c47c6c ("NFSv4.2: Change the default >>>>> KConfig value for READ_PLUS") as one leading to NULL pointer exception >>>>> when mounting NFS root on NFSv4 client: >>>>> >>>>> [ 25.739003] systemd[1]: Set hostname to <odroidhc1>. >>>>> [ 25.771714] systemd[1]: Failed to bump fs.file-max, ignoring: Invalid >>>>> argument >>>>> [ 26.199478] 8<--- cut here --- >>>>> [ 26.201366] Unable to handle kernel NULL pointer dereference at >>>>> virtual address 00000004 >>>>> ... >>>>> [ 26.555522] mmiocpy from xdr_inline_decode+0xec/0x16c >>>>> [ 26.560628] xdr_inline_decode from nfs4_xdr_dec_read_plus+0x178/0x358 >>>>> [ 26.567130] nfs4_xdr_dec_read_plus from call_decode+0x204/0x304 >>>>> >>>>> Full OOPS attached. Full log available here: >>>>> https://krzk.eu/#/builders/21/builds/3901/steps/15/logs/serial0 >>>>> >>>>> Disabling NFS_V4_2_READ_PLUS fixes the issue, so obviously the commit is >>>>> not the cause, but rather making it default caused the regression. >>>>> >>>>> I did not make the bisect yet which commit introduced it, if every >>>>> config includes NFS_V4_2_READ_PLUS. >>>> >>>> When every kernel is built with NFS_V4_2_READ_PLUS, bisect pointed to: >>>> d3b00a802c84 ("NFS: Replace the READ_PLUS decoding code") >>>> >>>> commit d3b00a802c845a6021148ce2e669b5a0b5729959 >>>> Author: Anna Schumaker <Anna.Schumaker@xxxxxxxxxx> >>>> Date: Thu Jul 21 14:21:34 2022 -0400 >>>> >>>> NFS: Replace the READ_PLUS decoding code >>>> >>>> We now take a 2-step process that allows us to place data and hole >>>> segments directly at their final position in the xdr_stream without >>>> needing to do a bunch of redundant copies to expand holes. Due to the >>>> variable lengths of each segment, the xdr metadata might cross page >>>> boundaries which I account for by setting a small scratch buffer so >>>> xdr_inline_decode() won't fail. >>>> >>>> Signed-off-by: Anna Schumaker <Anna.Schumaker@xxxxxxxxxx> >>>> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> >>>> >>>> With a trace: >>>> [ 25.898462] systemd[1]: Set hostname to <odroidhc1>. >>>> [ 25.933746] systemd[1]: Failed to bump fs.file-max, ignoring: Invalid >>>> argument >>>> [ 25.986237] random: crng init done >>>> [ 26.264564] 8<--- cut here --- >>>> [ 26.266823] Unable to handle kernel NULL pointer dereference at >>>> virtual address 00000fe8 >>>> ... >>>> [ 26.597263] nfs4_xdr_dec_read_plus from call_decode+0x204/0x304 >>>> [ 26.603222] call_decode from __rpc_execute+0xd0/0x890 >>>> [ 26.608328] __rpc_execute from rpc_async_schedule+0x1c/0x34 >>>> [ 26.613960] rpc_async_schedule from process_one_work+0x294/0x790 >>>> [ 26.620030] process_one_work from worker_thread+0x54/0x518 >>>> [ 26.625570] worker_thread from kthread+0xf4/0x128 >>>> [ 26.630336] kthread from ret_from_fork+0x14/0x2c >>>> >>> >>> Is this test being run against a 6.2-rc2 server, or is it an older server platform? We know there were bugs in older server implementations, so the question is whether this might be a problem with handling a bad/corrupt RPC reply from the server, or whether it is happening against code that is supposed to have been fixed? >> >> I would say that buggy server should not cause NULL pointer dereferences >> on the client. Otherwise this is a perfect recipe for a rogue server in >> the network to start crashing clients and running exploits... Imagine a >> compromised machine (through some other means) in a local company >> network running now a server with NFS share "HR salary data" or "HR >> planned layoffs", where unsuspected people in that network access it >> leading to exploit of NFS code on their side... >> >> Server is Raspberry Pi 3 kernel: 5.10.92-2-rpi-legacy-ARCH >> >> Which points that it is not latest stable, so anyway I need to update. > > I updated the kernel to 5.15.84-3-rpi-ARCH which is pretty close to > latest stable and I can reproduce the issue. Therefore: > 1. It is visible on two stable (one new, one old) kernels on the server, > 2. Buggy or rogue server should not cause NULL pointer on remote devices... > The nfsd READ_PLUS code is borked up and until 6.2-rc1. I thought we had a server option to disable that code, but it seems as if that is not the case. Chuck + Anna, can we please send a stable patch to rip out that code altogether from all the older versions? If we want to enable READ_PLUS by default on the client, then we cannot do so if the majority of NFSv4.2 servers out there are running a borked implementation. I do agree that we cannot allow buggy servers to cause memory corruption in the client code, so I propose that we revert the Kconfig default setting change again until both the client code and the legacy servers have been fixed. Anna? Thanks Trond
