Re: refcount underflow in nfsd41_destroy_cb

[Jan Psota <jasiu@belsznica.pl>]

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> I thought I read in the initial report that you were seeing this
> problem only on v5.6-rc6. What is the earliest kernel release
> where you saw refcount UaF warnings from nfsd4_destroy_cb?
> 
I didn't noticed that earlier too, because until connection breakage on
WireGuard I did not have any problems related. But when you are asking,
I found it in my Pentium G2020 system too since 5.5.4 kernel and 5.4.2
looks not affected (I have logs since 01 Jan and fault begin to appear
on Feb 21, when I switched from 5.4.2 to 5.5.4 kernel a day before)

$ journalctl | grep nfsd41_destroy_cb
lut 21 01:07:58 mordimer kernel:  nfsd41_destroy_cb+0x2c/0x40 [nfsd]
lut 27 01:01:12 mordimer kernel:  nfsd41_destroy_cb+0x2c/0x40 [nfsd]
mar 03 00:59:01 mordimer kernel:  nfsd41_destroy_cb+0x2c/0x40 [nfsd]
mar 03 23:03:02 mordimer kernel:  nfsd41_destroy_cb+0x2c/0x40 [nfsd]
mar 11 11:52:42 mordimer kernel:  nfsd41_destroy_cb+0x2c/0x40 [nfsd]
mar 13 01:12:02 mordimer kernel:  nfsd41_destroy_cb+0x2c/0x40 [nfsd]
mar 14 14:31:39 mordimer kernel:  nfsd41_destroy_cb+0x2c/0x40 [nfsd]
mar 15 20:56:56 mordimer kernel:  nfsd41_destroy_cb+0x2c/0x40 [nfsd]
mar 17 15:58:32 mordimer kernel:  nfsd41_destroy_cb+0x2c/0x40 [nfsd]
mar 22 15:24:03 mordimer kernel:  nfsd41_destroy_cb+0x2c/0x40 [nfsd]

I attach NFS part of my .config and a screen dump of menuconfig.

[-- Attachment #2: nfs.config --]
[-- Type: application/octet-stream, Size: 1037 bytes --]

CONFIG_NETWORK_FILESYSTEMS=y
CONFIG_NFS_FS=m
# CONFIG_NFS_V2 is not set
CONFIG_NFS_V3=m
CONFIG_NFS_V3_ACL=y
CONFIG_NFS_V4=m
# CONFIG_NFS_SWAP is not set
CONFIG_NFS_V4_1=y
CONFIG_NFS_V4_2=y
CONFIG_PNFS_FILE_LAYOUT=m
CONFIG_PNFS_BLOCK=m
CONFIG_PNFS_FLEXFILE_LAYOUT=m
CONFIG_NFS_V4_1_IMPLEMENTATION_ID_DOMAIN="kernel.org"
# CONFIG_NFS_V4_1_MIGRATION is not set
CONFIG_NFS_V4_SECURITY_LABEL=y
# CONFIG_NFS_FSCACHE is not set
# CONFIG_NFS_USE_LEGACY_DNS is not set
CONFIG_NFS_USE_KERNEL_DNS=y
CONFIG_NFS_DISABLE_UDP_SUPPORT=y
CONFIG_NFSD=m
CONFIG_NFSD_V2_ACL=y
CONFIG_NFSD_V3=y
CONFIG_NFSD_V3_ACL=y
CONFIG_NFSD_V4=y
CONFIG_NFSD_PNFS=y
CONFIG_NFSD_BLOCKLAYOUT=y
CONFIG_NFSD_SCSILAYOUT=y
# CONFIG_NFSD_FLEXFILELAYOUT is not set
# CONFIG_NFSD_V4_2_INTER_SSC is not set
# CONFIG_NFSD_V4_SECURITY_LABEL is not set
CONFIG_GRACE_PERIOD=m
CONFIG_LOCKD=m
CONFIG_LOCKD_V4=y
CONFIG_NFS_ACL_SUPPORT=m
CONFIG_NFS_COMMON=y
CONFIG_SUNRPC=m
CONFIG_SUNRPC_GSS=m
CONFIG_SUNRPC_BACKCHANNEL=y
# CONFIG_RPCSEC_GSS_KRB5 is not set
# CONFIG_SUNRPC_DEBUG is not set

[-- Attachment #3: nfs-config.txt --]
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│ │         --- Network File Systems                                                        │ │  
│ │         <M>   NFS client support                                                        │ │  
│ │         < >     NFS client support for NFS version 2                                    │ │  
│ │         <M>     NFS client support for NFS version 3                                    │ │  
│ │         [*]       NFS client support for the NFSv3 ACL protocol extension               │ │  
│ │         <M>     NFS client support for NFS version 4                                    │ │  
│ │         [ ]     Provide swap over NFS support                                           │ │  
│ │         [*]   NFS client support for NFSv4.1                                            │ │  
│ │         [*]     NFS client support for NFSv4.2                                          │ │  
│ │         (kernel.org) NFSv4.1 Implementation ID Domain                                   │ │  
│ │         [ ]     NFSv4.1 client support for migration                                    │ │  
│ │         [ ]   Provide NFS client caching support                                        │ │  
│ │         [ ]   Use the legacy NFS DNS resolver                                           │ │  
│ │         [*]   NFS: Disable NFS UDP protocol support                                     │ │  
│ │         <M>   NFS server support                                                        │ │  
│ │         -*-     NFS server support for NFS version 3                                    │ │  
│ │         [*]       NFS server support for the NFSv3 ACL protocol extension               │ │  
│ │         [*]     NFS server support for NFS version 4                                    │ │  
│ │         [*]   NFSv4.1 server support for pNFS block layouts                             │ │  
│ │         [*]   NFSv4.1 server support for pNFS SCSI layouts                              │ │  
│ │         [ ]   NFSv4.1 server support for pNFS Flex File layouts                         │ │  
│ │         [ ]   NFSv4.2 inter server to server COPY                                       │ │  
│ │         [ ]   Provide Security Label support for NFSv4 server                           │ │  
│ │         < >   Secure RPC: Kerberos V mechanism                                          │ │  
│ │         [ ]   RPC: Enable dprintk debugging                                             │ │