linux-kernel - Re: Regression: NULL pointer dereference after NFS_V4_2_READ

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Date:   Fri, 10 Feb 2023 09:53:00 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Anna Schumaker <schumaker.anna@...il.com>
Cc:     Trond Myklebust <trondmy@...merspace.com>,
        Anna Schumaker <Anna.Schumaker@...app.com>,
        linux-nfs <linux-nfs@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "regressions@...ts.linux.dev" <regressions@...ts.linux.dev>
Subject: Re: Regression: NULL pointer dereference after NFS_V4_2_READ_PLUS
 (commit 7fd461c47)

On 10/02/2023 09:41, Krzysztof Kozlowski wrote:
> 
> 
>>
>> I was also wondering if it would be possible to turn on KASAN in your
>> kernel, which should give us a little more info?
> 
> I'll try with KASAN.

Not much from the KASAN, except that kernel
continues to boot and runs:

[   44.722846] vdd_vmem: disabling
[   44.793465] systemd[1]: Hostname set to <odroidhc1>.
[   45.357929] systemd[1]: bpf-lsm: BPF LSM hook not enabled in the kernel, BPF LSM not supported
[   45.980476] ==================================================================
[   45.986372] BUG: KASAN: null-ptr-deref in xdr_inline_decode+0x140/0x200
[   45.992929] Read of size 4092 at addr 00000004 by task kworker/u16:3/71
[   45.999513] 
[   46.000940] CPU: 6 PID: 71 Comm: kworker/u16:3 Not tainted 6.2.0-rc7-00018-g0983f6bf2bfc #222
[   46.009504] Hardware name: Samsung Exynos (Flattened Device Tree)
[   46.015542] Workqueue: rpciod rpc_async_schedule
[   46.020123]  unwind_backtrace from show_stack+0x10/0x14
[   46.025323]  show_stack from dump_stack_lvl+0x58/0x70
[   46.030301]  dump_stack_lvl from kasan_report+0xa8/0xe0
[   46.035501]  kasan_report from kasan_check_range+0x94/0x1a0
[   46.041048]  kasan_check_range from memcpy+0x28/0x68
[   46.045985]  memcpy from xdr_inline_decode+0x140/0x200
[   46.051098]  xdr_inline_decode from nfs4_xdr_dec_read_plus+0x298/0x5b8
[   46.057602]  nfs4_xdr_dec_read_plus from call_decode+0x39c/0x530
[   46.063581]  call_decode from __rpc_execute+0x1f4/0xc5c
[   46.068776]  __rpc_execute from rpc_async_schedule+0x2c/0x4c
[   46.074411]  rpc_async_schedule from process_one_work+0x51c/0xc44
[   46.080478]  process_one_work from worker_thread+0x9c/0x7c0
[   46.086022]  worker_thread from kthread+0x16c/0x1b8
[   46.090872]  kthread from ret_from_fork+0x14/0x2c
[   46.095550] Exception stack(0xf0ba3fb0 to 0xf0ba3ff8)
[   46.100580] 3fa0:                                     00000000 00000000 00000000 00000000
[   46.108740] 3fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[   46.116885] 3fe0: 00000000 00000000 00000000 00000000 00000013 00000000
[   46.123461] ==================================================================
[   46.130774] Disabling lock debugging due to kernel taint
[   50.848579] systemd[1]: Queued start job for default target Graphical Interface.
[   50.877068] systemd[1]: Created slice Slice /system/getty.


Decoded stacktrace is (this is master branch):

[   46.020123] unwind_backtrace from show_stack (arch/arm/kernel/traps.c:258) 
[   46.025323] show_stack from dump_stack_lvl (lib/dump_stack.c:107 (discriminator 4)) 
[   46.030301] dump_stack_lvl from kasan_report (mm/kasan/report.c:184 mm/kasan/report.c:519) 
[   46.035501] kasan_report from kasan_check_range (mm/kasan/generic.c:173 mm/kasan/generic.c:189) 
[   46.041048] kasan_check_range from memcpy (mm/kasan/shadow.c:65) 
[   46.045985] memcpy from xdr_inline_decode (net/sunrpc/xdr.c:1419 net/sunrpc/xdr.c:1454) 
[   46.051098] xdr_inline_decode from nfs4_xdr_dec_read_plus (fs/nfs/nfs42xdr.c:1063 fs/nfs/nfs42xdr.c:1149 fs/nfs/nfs42xdr.c:1360 fs/nfs/nfs42xdr.c:1343) 
[   46.057602] nfs4_xdr_dec_read_plus from call_decode (net/sunrpc/clnt.c:2595) 
[   46.063581] call_decode from __rpc_execute (include/asm-generic/bitops/generic-non-atomic.h:128 net/sunrpc/sched.c:954) 
[   46.068776] __rpc_execute from rpc_async_schedule (include/linux/sched/mm.h:336 net/sunrpc/sched.c:1035) 
[   46.074411] rpc_async_schedule from process_one_work (kernel/workqueue.c:2294) 
[   46.080478] process_one_work from worker_thread (include/linux/list.h:292 kernel/workqueue.c:2437) 
[   46.086022] worker_thread from kthread (kernel/kthread.c:376) 
[   46.090872] kthread from ret_from_fork (arch/arm/kernel/entry-common.S:149) 


Best regards,
Krzysztof