Dnsmasq unable to access log file
Solution 1:
I know this answer comes late, but I found the solution. Just remove the log file and restart dnsmasq
rm /tmp/dnsmasq.log
systemctl restart dnsmasq
A new log file will be generated
EDIT: The fix above is only temporary; next time dnsmasq starts it will fail again. To fix this I uninstalled it with apt and compiled it from source instead
apt remove dnsmasq
cd ~/Downloads
git clone git://thekelleys.org.uk/dnsmasq.git
cd dnsmasq
make install (as root)