find . -type f -print0 | xargs -0 chmod 644

touch "hullo world"
chmod 777 "hullo*"
find . -type f -print0 | xargs -0 chmod 644

/bin/chmod: cannot access `./hello': No such file or directory
/bin/chmod: cannot access `world': No such file or directory

find . -type f -exec chmod 644 {} ;

find . -type f -print0 | xargs -0 -I {} chmod 644 {}