> On Jan 9, 2023, at 10:07, Chuck Lever III <chuck.lever@xxxxxxxxxx> wrote: > > > >> On Jan 9, 2023, at 9:44 AM, Trond Myklebust <trondmy@xxxxxxxxxxxxxxx> wrote: >> >> >> >>> 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 > > or malicious, or non-Linux, > > >> 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. > > I stand ready to receive and apply server-side fixes, as you suggested. > > However IMO it would be most responsible to go straight for a client code fix. The Kconfig setting is a red herring (as delicious as that might sound). Any thoughts about how difficult that fix might be? > A client fix is necessary, but not sufficient. The older server READ_PLUS code is slower than ordinary read for several filesystems, since it relies upon the (often poor) performance of lseek(SEEK_HOLE). Leaving legacy servers as is, would therefore still cause regressions for clients that default to trying READ_PLUS, even if the code is fixed to not Oops. As for the client fix, I’m leaving that to Anna, since she owns the READ_PLUS feature. I stand ready to revert the Kconfig setting if these fixes cannot be made in the 6.2 time frame. _________________________________ Trond Myklebust Linux NFS client maintainer, Hammerspace trond.myklebust@xxxxxxxxxxxxxxx
