[Samsung Gear S3] adfree:
No idea if similar with unmodified Combination Firmware BQC2... will check later...

With my rooted BQC5:

sh-3.2# cd bin
sh-3.2# ls -1al su
-rwxr-xrwx 1 root root 31608 Jun 2 20:30 su
sh-3.2# rm su
rm: cannot remove `su': Read-only file system
sh-3.2# mount -o remount,rw /
sh-3.2# rm su
rm: cannot remove `su': Permission denied
sh-3.2# mv su suu
mv: cannot move `su' to `suu': Permission denied
sh-3.2# mkdir test
mkdir: cannot create directory `test': Permission denied
sh-3.2# chmod +u su
sh-3.2# ls -1al su
-rwxrwxrwx 1 root root 31608 Jun 2 20:30 su
sh-3.2# su
sh-3.2# su -app
su: invalid option -- 'a'
Usage: su [options] [LOGIN]

Options:
-c, --command COMMAND pass COMMAND to the invoked shell
-h, --help display this help message and exit
-, -l, --login make the shell a login shell
-m, -p,
--preserve-environment do not reset environment variables, and
keep the same shell
-s, --shell SHELL use SHELL instead of the default in passwd

sh-3.2# su --app
su: unrecognized option '--app'
Usage: su [options] [LOGIN]

Options:
-c, --command COMMAND pass COMMAND to the invoked shell
-h, --help display this help message and exit
-, -l, --login make the shell a login shell
-m, -p,
--preserve-environment do not reset environment variables, and
keep the same shell
-s, --shell SHELL use SHELL instead of the default in passwd

It looks like mount is success... but Commands like rm, mv, mkdir are blocked...

But chmod seems to work...

:confused:

Hmmmmmmmmmmmmmmmmmmmmm... so I can write to rootfs.img as it seems...

Best Regards

Edit 1.

sh-3.2# cd /usr/bin
sh-3.2# ls -1al testmode
ls: cannot access testmode: Permission denied
sh-3.2# stat testmode
stat: cannot stat `testmode': Permission denied
sh-3.2# chattr -i testmode
chattr: Permission denied while trying to stat testmode
sh-3.2# chmod +x testmode
chmod: cannot access `testmode': Permission denied
sh-3.2# rm testmode
rm: cannot remove `testmode': Permission denied
sh-3.2# mv testmode test
mv: cannot stat `testmode': Permission denied

Edit 2.

sh-3.2# tinybox --help
TinyBox v0.1 multi-call binary
Copyright (c) 2013 Samsung Electronics Co., Ltd.
Licensed under Apache License, Version 2.0
See source distribution for full notice.

Usage: tinybox [module] [arguments]...
or: tinybox --list
or: module [arguments]...

TinyBox is a multi-call binary that contains many Linux commandline
utilites in a single executable. Usualy when it's called via symbolic link
TinyBox executes the module corresponding to the name of symbolic link.

Currently defined modules:
whoami - Return effective username of the current user
who - Display who is on the system
uname - Print system information
udhcpd - micro Dynamic Host Configuration Protocol daemon
true - Return success termination code
syslogd - System logging daemon
sync - causes all buffered modifications to file metadata and data to be written to the underlying filesystems
sleep - Pause for NUMBER seconds
seq - Count from FIRST to LAST, by INCREMENT
sed - stream editor for filtering and transforming text
route - show / manipulate the IP routing table
rmdir - remove directories
rm - remove the file(s)
pwd - Print working directory
printenv - Print environment variables
nice - run a command with modified niceness value
umount - Unmount listed filesystems
mount - Mounts filesystems
mktemp - Create new unique file/directory
mknod - Create a special file with a given type
mkdir - make directories
ln - make links between files
klogd - A kernel logging daemon, which reads messages from /proc/kmsg and sends them to syslog
sendevent - send a specific event to a input device
auto_scroll - automatic scroll utility
id - Print user and group ID
head - Print the beginning of a file
fsync - causes all buffered modifications to file metadata anddata to be written to the underlying filesystems of given file
mkfs.vfat - Creates VFAT filesystem on a given device/partition/file.
fsck.vfat - check consistency of FAT filesystem
false - Return failure termination code
env - Invoke command in an altered environment
dirname - extract directory path from input path
chroot - Run command within a new root directory
chmod - change mode of the file(s)
cat - concatenate files and print on the standard output
basename - Return non-directory portion of a pathname removing suffix
awk - pattern scanning and text processing language
attr - extended file attribute management tools

Edit 3.

Interesting Links... for Linux Noob like me...

https://unix.stackexchange.com/questions/206594/why-cant-i-delete-this-file-as-root