Messages in this thread | | | Date | Mon, 23 Jan 2023 08:58:43 +0100 | Subject | Re: Regression: NULL pointer dereference after NFS_V4_2_READ_PLUS (commit 7fd461c47) | From | Krzysztof Kozlowski <> |
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On 22/01/2023 23:25, Anna Schumaker wrote: > Hi Krzysztof, > > On Mon, Jan 9, 2023 at 3:46 AM Krzysztof Kozlowski > <krzysztof.kozlowski@linaro.org> 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@linaro.org> wrote: >>>>> >>>>> [You don't often get email from krzysztof.kozlowski@linaro.org. 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@Netapp.com> >>>>> 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@Netapp.com> >>>>> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com> >>>>> >>>>> 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... > > I'm still working on this issue, but I haven't been able to reproduce > it with my setup at all yet. I was hoping I could ask you a couple of > questions? > > - Are both client and server run on a Raspberry Pi 3?
No, server is Rpi3, client is Odroid HC1.
> - Is there a specific workload that triggers the bug, or is it just > during boot when using nfsroot?
No specific workload - mounting system with nfsroot. You have there full logs as it is reproducible every time.
> - Would it be possible to get a Wireshark network trace of the crash > (you'll have to run this on the server due to nfsroot).
I'll check.
> - Can you share your export options from /etc/exports and the mount > options that the client uses?
exports are the same since like 5 years or more:
/srv/nfs/odroidhc1 192.168.1.0/24(rw,async,no_root_squash,no_subtree_check) /srv/nfs/odroidhc1-home 192.168.1.0/24(rw,async,no_root_squash,no_subtree_check)
> > Thanks, > Anna > >> >> Best regards, >> Krzysztof >>
Best regards, Krzysztof
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