: version 1.34 released April 25th, 2005	SLES9	RHEL4/FedoraCore3, SuseWorkstation 9.2 and other 2.6.8 and 2.6.9 based kernels	current mainline
cifs.ko kernel module (source code)	fs/cifs/ src 1.34a	fs/cifs src 1.34a	fs/cifs src 1.50
cifs.ko kernel module (prebuilt for x86 default kernel)	cifs.ko 1.33	cifs.ko 1.33
mount.cifs cifs mount helper (source code)	same	same	mount.cifs.c
mount.cifs (prebuilt x86)	same	same	mount.cifs (1.8 for x86)
umount.cifs (rarely needed, except for certain types of user unmounts) (source code)	same	same	umount.cifs.c (0.4 for x86)
umount.cifs (rarely needed) (prebuilt x86 binary)	same	same	umount.cifs
man pages	same	same	mount.cifs umount.cifs

For Linux 2.6 the cifs vfs does not require a distinct download (it is in starting in kernel release 2.5.42). Kernel version 2.6.10 contains version 1.28 of the cifs vfs. The current version is always available via the bitkeeper tree at http://cifs.bkbits.net/linux-2.5cifs and a relatively recent version is also available by downloading replacement files that can be used in place of those in the fs/cifs directory.

Source for fairly current cifs vfs also can be retrieved via subversion from samba svn linux-cifs-client project:
svn co svn://svnanon.samba.org/linux-cifs-client/branches

The most current 2.6 source is hosted at cifs.bkbits.net (requires installation of BitKeeper to download) As kernel developers switch to newer tooling, the cifs tree may be made available via other mechanisms in the future.
Historical versions can be found at http://pserver.samba.org/samba/ftp/cifs-cvs/
including a 2.4 kernel port : Latest 2.4 Release (gz containing cifs vfs source files and patch for kernel makefile and configure)

CIFS Download