kernel crashes at nfs4_get_valid_delegation function

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Environment

SUSE Linux Enterprise Server 15 SP2

Situation

A SLES15 SP2 system running kernel version 5.3.18-22.2 crashes.
The dmesg.txt of the kernel kdump stack trace shows the following:
[344815.414662] BUG: unable to handle page fault for address: ffffffffffffffb0
[344815.414667] #PF: supervisor read access in kernel mode
[344815.414669] #PF: error_code(0x0000) - not-present page
[344815.414671] PGD 787dc0f067 P4D 787dc0f067 PUD 787dc11067 PMD 0
[344815.414675] Oops: 0000 [#1] SMP PTI
[344815.414677] CPU: 9 PID: 116164 Comm: kworker/u256:9 Kdump: loaded Tainted: P OE 5.3.18-22-default #1 SLE15-SP2 (unreleased)
[344815.414680] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 12/12/2018
[344815.414701] Workqueue: rpciod rpc_async_schedule [sunrpc]
[344815.414718] RIP: 0010:nfs4_get_valid_delegation+0x6/0x30 [nfsv4]
[344815.414720] Code: ff ff ff eb 9b e8 5a 44 4a c4 66 2e 0f 1f 84 00 00 00 00 00 66 66 66 66 90 f0 80 4f 48 08 c3 0f 1f 44 00 00 66 66 66 66 90 53 <48> 8b 5f b0 31 f6 48 89 df e8 9c fa ff ff 84 c0 b8 00 00 00 00 48
[344815.414724] RSP: 0018:ffffba19c26ebdf8 EFLAGS: 00010246
[344815.414725] RAX: ffff9d0396708fc0 RBX: ffff9cef184f7c00 RCX: 0000000000000004
[344815.414727] RDX: 0000000000008000 RSI: 0000000000000001 RDI: 0000000000000000
[344815.414728] RBP: ffff9d4995f77c00 R08: 0000646f69637072 R09: 8080808080808080
[344815.414730] R10: ffffba19d84476d0 R11: fefefefefefefeff R12: 0000000000000004
[344815.414731] R13: ffff9d49a4276c00 R14: ffffffffc0ae7170 R15: ffffffffc0ae3ef0
[344815.414733] FS: 0000000000000000(0000) GS:ffff9d49b6240000(0000) knlGS:0000000000000000
[344815.414735] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[344815.414737] CR2: ffffffffffffffb0 CR3: 0000007dd139e006 CR4: 00000000000606e0
[344815.414787] Call Trace:
[344815.414799] nfs4_open_prepare+0x80/0x1d0 [nfsv4]
[344815.414812] __rpc_execute+0x83/0x420 [sunrpc]
[344815.414822] rpc_async_schedule+0x29/0x40 [sunrpc]
[344815.414830] process_one_work+0x1f4/0x3e0
[344815.414833] worker_thread+0x2d/0x3e0
[344815.414835] ? process_one_work+0x3e0/0x3e0
[344815.414838] kthread+0x10d/0x130
[344815.414840] ? kthread_park+0xa0/0xa0
[344815.414844] ret_from_fork+0x35/0x40

Resolution

This is a bug that is already fixed in kernel version 5.3.18-24.9.1 or later.

Cause

The issue is caused by a NULL deference bug in the nfsv4 module of the kernel version 5.3.18-22.2.

Status

Top Issue

Additional Information

The release notes for the kernel patch "SUSE-SLE-Module-Basesystem-15-SP2-2020-2105" :
- nfs: fix NULL deference in nfs4_get_valid_delegation.

The changelog for the fix:
# rpm -q --changelog kernel-default
...
* Fri May 22 2020 pvorel@suse.cz
- nfs: fix NULL deference in nfs4_get_valid_delegation.
- commit ee8a543

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