Ncat 7.94 "breaks udptunnel autopkgtest" on Debian. #2685
Comments
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I was about to open a bug report now that I confirmed it's an issue, thanks! This regression was introduced on 4e6c8fe, I confirm the commit previous to this one does not trigger the issue. I noticed that this only happens when running inside a script, I can't reproduce it manually/interactively. This is the script I've used to #!/bin/bash
# Bail out and tell git this commit is untestable.
untestable() {
git reset --hard
exit 125
}
# Build ncat locally.
autoconf || untestable
./configure --build=x86_64-linux-gnu --includedir=\${prefix}/include --disable-option-checking --disable-silent-rules --libdir=\${prefix}/lib/x86_64-linux-gnu --disable-maintainer-mode --disable-dependency-tracking --with-liblua=/usr --with-liblinear --without-zenmap --without-ndiff --enable-ipv6 STRIP=/bin/true || untestable
make -j16 build-ncat || untestable
# Add extra verbosity and fail on any errors.
set -euo pipefail
set -x
# Variables.
UDPSERVER_PORT=5500
TX_FILE="tx.data"
RX_FILE="rx.data"
# Point to locally built ncat.
ncat() {
./ncat/ncat "$@"
}
# Double check we're running the right version.
ncat --version
# Start UDP server.
ncat -u -l 127.0.0.1 $UDPSERVER_PORT -o $RX_FILE &
sleep 3
# Create TX_FILE.
# Trailing whitespaces were left on purpose.
cat <<EOF > $TX_FILE
THIS
IS
THE
DATA
SEND
OVER
UDPTunnel
EOF
# Send UDP data to the server.
cat $TX_FILE | ncat -u 127.0.0.1 $UDPSERVER_PORT
# Check if RX_FILE contains the data sent.
if ! diff $TX_FILE $RX_FILE; then
echo "RX_FILE is not equals TX_FILE"
# Cleanup git repo, for git bisect.
git reset --hard
exit 1
else
# If we got here, then it worked.
git reset --hard
exit 0
fi |
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The issue at the core here is what to do when EOF is received on STDIN. Previously, Ncat did not quit in this case for SOCK_DGRAM (i.e. UDP) listen mode, but it does do so for non-TCP SOCK_STREAM (i.e. SCTP). The commit which introduced this issue unified the listen mode code but did not handle the UDP case, which fell under the "non-TCP" part of the logic. The fix, which will be synchronized shortly, is for listen mode to only handle EOF on STDIN specially in the case of SOCK_STREAM (TCP and SCTP), restoring the previous behavior of UDP mode. A helpful enhancement to Ncat would be to support the |
Debian Bug #1039613 reports that:
The Nmap version in testing is "7.94+dfsg1-1". A further comment on the Debian bug notes:
They say that version of Ncat in testing (which seems to be 7.93+dfsg1-1) still works. And given that we did make several Ncat changes in 7.94, we should probably investigate and fix whatever might have caused this apparent regression.
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