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The FTP server currently supports the following FTP requests; case is not distinguished.
The remaining FTP requests specified in RFC 959 are recognized, but not implemented.
The FTP server will abort an active file transfer only when the ABOR command is preceded by a Telnet ‘Interrupt Process’ (IP) signal and a Telnet ‘Synch’ signal in the command Telnet stream, as described in RFC 959.
in.ftpd interprets file names according to the ‘globbing’ conventions used by sh(1) . This allows users to utilize the metacharacters: * ? [ ] { } ~
in.ftpd authenticates users according to four rules.
- The user name must be in the password data base, /etc/passwd, and have a password that is not null. A password must always be provided by the client before any file operations may be performed.
- If the user name appears in the file /etc/ftpusers, ftp access is denied.
- ftp access is denied if the user’s shell (from /etc/passwd) is not listed in the file /etc/shells. If the file /etc/shells does not exist, then the user’s shell must be one of the following:
/usr/bin/sh /usr/bin/csh /usr/bin/ksh /usr/bin/jsh /bin/sh /bin/csh /bin/ksh /bin/jsh /sbin/sh /sbin/jsh
For anonymous ftp users, in.ftpd takes special measures to restrict the client’s access privileges. The server performs a chroot(2) command to the home directory of the ‘ftp’ user. In order that system security is not breached, it is recommended that the ‘ftp’ subtree be constructed with care; the following rules are suggested.
ld.so*
libc.so*
libdl.so*
libintl.so*
libw.so*
libnsl.so*
libsocket.so*
nss_nis.so*
nss_nisplus.so*
nss_dns.so*
nss_files.so*
straddr.so*
/dev/zero
/dev/tcp
/dev/udp
/dev/ticotsord
Set the read and write mode on these nodes to 666 so that passive ftp will not fail with ‘permission denied’ errors.
To set up anonymous ftp, add the following entry to the /etc/passwd file. In this case, /export/ftp was chosen to be the anonymous ftp area, and the shell is the non-existent file /nosuchshell. This prevents users from logging in as the ftp user. ftp:x:30000:30000:Anonymous FTP:/export/ftp:/nosuchshell Add the following entry to /etc/shadow: ftp:NP:6445::::::
The following is a shell script that will set up the anonymous ftp area. It presumes that names are resolved using NIS .
#!/bin/sh
# script to setup anonymous ftp area
#
# handle the optional command line argument
case $# in
# the default location for the anon ftp comes from the passwd file
0) ftphome="‘grep ’^ftp:’ /etc/passwd | cut -d: -f6‘"
;;
1) if [ "$1" = "start" ]; then
ftphome="‘grep ’^ftp:’ /etc/passwd | cut -d: -f6‘"
else
ftphome=$1
fi
;;
*) echo "Usage: $0 [anon-ftp-root]"
exit 1
;;
esac
if [ -z "${ftphome}" ]; then
echo "$0: ftphome must be non-null"
exit 2
fi
# This script assumes that ftphome is neither / nor /usr so ...
if [ "${ftphome}" = "/" -o "${ftphome}" = "/usr" ]; then
echo "$0: ftphome must not be / or /usr"
exit 2
fi
# If ftphome does not exist but parent does, create ftphome
if [ ! -d ${ftphome} ]; then
# lack of -p below is intentional
mkdir ${ftphome}
fi
echo Setting up anonymous ftp area ${ftphome}
# Ensure that the /usr/bin directory exists
if [ ! -d ${ftphome}/usr/bin ]; then
mkdir -p ${ftphome}/usr/bin
fi
cp /usr/bin/ls ${ftphome}/usr/bin
chmod 111 ${ftphome}/usr/bin/ls
# Now set the ownership and modes to match the man page
chown root ${ftphome}/usr/bin
chmod 555 ${ftphome}/usr/bin
# this may not be the right thing to do
# but we need the bin -> usr/bin link
if [ -r ${ftphome}/bin ]; then
mv -f ${ftphome}/bin ${ftphome}/Obin
fi
ln -s usr/bin ${ftphome}
# Ensure that the /usr/lib and /etc directories exist
if [ ! -d ${ftphome}/usr/lib ]; then
mkdir -p ${ftphome}/usr/lib
fi
if [ ! -d ${ftphome}/etc ]; then
mkdir -p ${ftphome}/etc
fi
#Most of the following are needed for basic operation, except
#for libnsl.so, nss_nis.so, libsocket.so, and straddr.so which are
#needed to resolve NIS names.
cp /usr/lib/ld.so /usr/lib/ld.so.1 ${ftphome}/usr/lib
for lib in libc libdl libintl libw libnsl libsocket \
nss_nis nss_nisplus nss_dns nss_files
do
cp /usr/lib/${lib}.so.1 ${ftphome}/usr/lib
rm -f ${ftphome}/usr/lib/${lib}.so
ln -s ./${lib}.so.1 ${ftphome}/usr/lib/${lib}.so
done
cp /usr/lib/straddr.so.2 ${ftphome}/usr/lib
rm -f ${ftphome}/usr/lib/straddr.so
ln -s ./straddr.so.2 ${ftphome}/usr/lib/straddr.so
cp /etc/passwd /etc/group /etc/netconfig ${ftphome}/etc
# Copy timezone database
mkdir -p ${ftphome}/usr/share/lib/zoneinfo
(cd ${ftphome}/usr/share/lib/zoneinfo
(cd /usr/share/lib/zoneinfo; find . -print | cpio -o) | cpio -imdu
find . -print | xargs chmod 555
find . -print | xargs chown root
)
chmod 555 ${ftphome}/usr/lib/*
chmod 444 ${ftphome}/etc/*
# Now set the ownership and modes
chown root ${ftphome}/usr/lib ${ftphome}/etc
chmod 555 ${ftphome}/usr/lib ${ftphome}/etc
# Ensure that the /dev directory exists
if [ ! -d ${ftphome}/dev ]; then
mkdir -p ${ftphome}/dev
fi
# make device nodes. ticotsord and udp are necessary for
# ’ls’ to resolve NIS names.
for device in zero tcp udp ticotsord
do
line=‘ls -lL /dev/${device} | sed -e ’s/,//’‘
major=‘echo $line | awk ’{print $5}’‘
minor=‘echo $line | awk ’{print $6}’‘
rm -f ${ftphome}/dev/${device}
mknod ${ftphome}/dev/${device} c ${major} ${minor}
done
chmod 666 ${ftphome}/dev/*
## Now set the ownership and modes
chown root ${ftphome}/dev
chmod 555 ${ftphome}/dev
if [ ! -d ${ftphome}/pub ]; then
mkdir -p ${ftphome}/pub
fi
chown ftp ${ftphome}/pub
chmod 777 ${ftphome}/pub
Postel, Jon, and Joyce Reynolds, File Transfer Protocol ( FTP ), RFC 959, Network Information Center, SRI International, Menlo Park, Calif., October 1985.
The server must run as the super-user to create sockets with privileged port numbers. It maintains an effective user id of the logged in user, reverting to the super-user only when binding addresses to sockets. The possible security holes have been extensively scrutinized, but are possibly incomplete.
/etc/ftpusers contains a list of users who cannot access the system; the format of the file is one user name per line.