unshare: bail if USER is empty (#88)

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

Author: AkihiroSuda

Dockerfile

@@ -37,5 +37,6 @@ ENV HOME /home/user
 RUN useradd --create-home --home-dir $HOME user \
 	&& chown -R user:user $HOME /run /tmp
 USER user
+ENV USER user
 ENTRYPOINT [ "img" ]
 CMD [ "--help" ]

unshare/unshare.c

@@ -266,6 +266,8 @@ static char *read_ranges(int type) {
 	uid = getuid();
 	user = getenv("USER");
 	user = user ? user : getlogin();
+	if (user == NULL)
+		bail("USER is unset");
 
 	while (getline(&line, &size, file) >= 0) {
 		if (strtol(line, &entry, 10) != uid || entry == line) {