[PATCH] adduser: Make home directory not world readable

[tito]

On Tue, 17 Jan 2023 14:10:48 +0100
Valentin <vakevk at gmail.com> wrote:

> adduser sets the mode of the newly created home directory to
> u+rwx g+rx o+rx (755). This allows every user on the system to read the
> directory.
> 
> This commit changes the mode to not give other users any permissions
> (750).
> 
> This is a better default. Home directories are likely to contain
> sensitive information, which you expect to not be world readable. If
> you really want your home directory to be world readable you can
> manually chmod it afterwards.
> 
> On the other hand, if the default is world readable, then inaction
> exposes sensitive information. This can happen by accident when you are
> not aware what mode adduser sets.
> 
> I could not find any reasoning for the current behavior. 755 has been
> used since the commit that created adduser.c in 2002. Neither the commit
> nor the file today contain an explanation.
> ---
>  loginutils/adduser.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/loginutils/adduser.c b/loginutils/adduser.c
> index d3c795afa..218fe1371 100644
> --- a/loginutils/adduser.c
> +++ b/loginutils/adduser.c
> @@ -278,9 +278,9 @@ int adduser_main(int argc UNUSED_PARAM, char **argv)
>  	umask(0);
>  	if (!(opts & OPT_DONT_MAKE_HOME)) {
>  		/* set the owner and group so it is owned by the new user,
> -		 * then fix up the permissions to 2755. Can't do it before
> +		 * then fix up the permissions to 2750. Can't do it before
>  		 * since chown will clear the setgid bit */
> -		int mkdir_err = mkdir(pw.pw_dir, 0755);
> +		int mkdir_err = mkdir(pw.pw_dir, 0750);
>  		if (mkdir_err == 0) {
>  			/* New home. Copy /etc/skel to it */
>  			const char *args[] = {
> @@ -299,7 +299,7 @@ int adduser_main(int argc UNUSED_PARAM, char **argv)
>  		}
>  		if ((mkdir_err != 0 && errno != EEXIST)
>  		 || chown(pw.pw_dir, pw.pw_uid, pw.pw_gid) != 0
> -		 || chmod(pw.pw_dir, 02755) != 0 /* set setgid bit on homedir */
> +		 || chmod(pw.pw_dir, 02750) != 0 /* set setgid bit on homedir */
>  		) {
>  			bb_simple_perror_msg(pw.pw_dir);
>  		}


Hi,
this is the default in debian as could be seen in /etc/adduser.conf:

# If DIR_MODE is set, directories will be created with the specified
# mode. Otherwise the default mode 0755 will be used.
DIR_MODE=0755

so busybox uses the default. This could be made a config option
with 755 as default or if we want to be more on the security 
side 750.

Ciao,
Tito