166 lines
7.4 KiB
ReStructuredText
166 lines
7.4 KiB
ReStructuredText
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.. SPDX-License-Identifier: GPL-2.0
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==========================
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KSMBD - SMB3 Kernel Server
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==========================
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KSMBD is a linux kernel server which implements SMB3 protocol in kernel space
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for sharing files over network.
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KSMBD architecture
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==================
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The subset of performance related operations belong in kernelspace and
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the other subset which belong to operations which are not really related with
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performance in userspace. So, DCE/RPC management that has historically resulted
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into number of buffer overflow issues and dangerous security bugs and user
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account management are implemented in user space as ksmbd.mountd.
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File operations that are related with performance (open/read/write/close etc.)
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in kernel space (ksmbd). This also allows for easier integration with VFS
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interface for all file operations.
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ksmbd (kernel daemon)
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---------------------
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When the server daemon is started, It starts up a forker thread
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(ksmbd/interface name) at initialization time and open a dedicated port 445
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for listening to SMB requests. Whenever new clients make request, Forker
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thread will accept the client connection and fork a new thread for dedicated
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communication channel between the client and the server. It allows for parallel
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processing of SMB requests(commands) from clients as well as allowing for new
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clients to make new connections. Each instance is named ksmbd/1~n(port number)
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to indicate connected clients. Depending on the SMB request types, each new
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thread can decide to pass through the commands to the user space (ksmbd.mountd),
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currently DCE/RPC commands are identified to be handled through the user space.
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To further utilize the linux kernel, it has been chosen to process the commands
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as workitems and to be executed in the handlers of the ksmbd-io kworker threads.
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It allows for multiplexing of the handlers as the kernel take care of initiating
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extra worker threads if the load is increased and vice versa, if the load is
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decreased it destroys the extra worker threads. So, after connection is
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established with client. Dedicated ksmbd/1..n(port number) takes complete
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ownership of receiving/parsing of SMB commands. Each received command is worked
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in parallel i.e., There can be multiple clients commands which are worked in
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parallel. After receiving each command a separated kernel workitem is prepared
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for each command which is further queued to be handled by ksmbd-io kworkers.
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So, each SMB workitem is queued to the kworkers. This allows the benefit of load
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sharing to be managed optimally by the default kernel and optimizing client
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performance by handling client commands in parallel.
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ksmbd.mountd (user space daemon)
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--------------------------------
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ksmbd.mountd is userspace process to, transfer user account and password that
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are registered using ksmbd.adduser (part of utils for user space). Further it
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allows sharing information parameters that parsed from smb.conf to ksmbd in
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kernel. For the execution part it has a daemon which is continuously running
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and connected to the kernel interface using netlink socket, it waits for the
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requests (dcerpc and share/user info). It handles RPC calls (at a minimum few
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dozen) that are most important for file server from NetShareEnum and
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NetServerGetInfo. Complete DCE/RPC response is prepared from the user space
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and passed over to the associated kernel thread for the client.
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KSMBD Feature Status
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====================
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============================== =================================================
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Feature name Status
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============================== =================================================
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Dialects Supported. SMB2.1 SMB3.0, SMB3.1.1 dialects
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(intentionally excludes security vulnerable SMB1
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dialect).
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Auto Negotiation Supported.
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Compound Request Supported.
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Oplock Cache Mechanism Supported.
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SMB2 leases(v1 lease) Supported.
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Directory leases(v2 lease) Planned for future.
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Multi-credits Supported.
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NTLM/NTLMv2 Supported.
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HMAC-SHA256 Signing Supported.
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Secure negotiate Supported.
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Signing Update Supported.
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Pre-authentication integrity Supported.
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SMB3 encryption(CCM, GCM) Supported. (CCM and GCM128 supported, GCM256 in
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progress)
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SMB direct(RDMA) Supported.
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SMB3 Multi-channel Partially Supported. Planned to implement
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replay/retry mechanisms for future.
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Receive Side Scaling mode Supported.
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SMB3.1.1 POSIX extension Supported.
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ACLs Partially Supported. only DACLs available, SACLs
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(auditing) is planned for the future. For
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ownership (SIDs) ksmbd generates random subauth
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values(then store it to disk) and use uid/gid
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get from inode as RID for local domain SID.
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The current acl implementation is limited to
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standalone server, not a domain member.
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Integration with Samba tools is being worked on
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to allow future support for running as a domain
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member.
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Kerberos Supported.
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Durable handle v1,v2 Planned for future.
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Persistent handle Planned for future.
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SMB2 notify Planned for future.
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Sparse file support Supported.
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DCE/RPC support Partially Supported. a few calls(NetShareEnumAll,
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NetServerGetInfo, SAMR, LSARPC) that are needed
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for file server handled via netlink interface
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from ksmbd.mountd. Additional integration with
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Samba tools and libraries via upcall is being
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investigated to allow support for additional
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DCE/RPC management calls (and future support
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for Witness protocol e.g.)
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ksmbd/nfsd interoperability Planned for future. The features that ksmbd
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support are Leases, Notify, ACLs and Share modes.
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============================== =================================================
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How to run
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==========
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1. Download ksmbd-tools and compile them.
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- https://github.com/cifsd-team/ksmbd-tools
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2. Create user/password for SMB share.
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# mkdir /etc/ksmbd/
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# ksmbd.adduser -a <Enter USERNAME for SMB share access>
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3. Create /etc/ksmbd/smb.conf file, add SMB share in smb.conf file
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- Refer smb.conf.example and
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https://github.com/cifsd-team/ksmbd-tools/blob/master/Documentation/configuration.txt
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4. Insert ksmbd.ko module
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# insmod ksmbd.ko
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5. Start ksmbd user space daemon
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# ksmbd.mountd
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6. Access share from Windows or Linux using CIFS
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Shutdown KSMBD
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==============
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1. kill user and kernel space daemon
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# sudo ksmbd.control -s
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How to turn debug print on
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==========================
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Each layer
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/sys/class/ksmbd-control/debug
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1. Enable all component prints
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# sudo ksmbd.control -d "all"
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2. Enable one of components (smb, auth, vfs, oplock, ipc, conn, rdma)
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# sudo ksmbd.control -d "smb"
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3. Show what prints are enabled.
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# cat /sys/class/ksmbd-control/debug
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[smb] auth vfs oplock ipc conn [rdma]
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4. Disable prints:
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If you try the selected component once more, It is disabled without brackets.
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