How /system/xbin/su works? - Android Q&A, Help & Troubleshooting

I used TWRP for installing the su command, and I installed SuperSU app from Google Play. It works.
The question - how su command works? It hasn't s-bit (it has -rwxr-xr-x, see below), so it can not change eUID by expected way. In what way it gets root's permissions?
Code:
[email protected]:/ $ id
uid=2000(shell) gid=2000(shell)
groups=1003(graphics),1004(input),1007(log),1011(adb),1015(sdcard_rw),1028(sdcard_r),3001(net_bt_admin),3002(net_bt),3003(inet),3006(net_bw_stats) context=u:r:shell:s0
[email protected]:/ $ su
[email protected]:/ # id
uid=0(root) gid=0(root) context=u:r:init:s0
[email protected]:/ # which su
/system/xbin/su
[email protected]:/ # ls -l /system/xbin/su
-rwxr-xr-x root root 75348 2016-10-29 22:31 su
[email protected]:/ #

Related

[Q] su only working from adb on 'rooted' Galaxy Tab 2

I used clockworkmod recovery and the cwm-root-gtab2.zip package to root my Tab 2. su appears to be installed ok, and I can get root permissions by running it from an adb shell:
~ $ adb shell
[email protected]:/ $ id
uid=2000(shell) gid=2000(shell) groups=1003(graphics),1004(input),1007(log),1009(mount),1011(adb),1015(sdcard_rw),1028(sdcard_r),3001(net_bt_admin),3002(net_bt),3003(inet),3006(net_bw_stats)
[email protected]:/ $ su
[email protected]:/ # id
uid=0(root) gid=0(root) groups=1003(graphics),1004(input),1007(log),1009(mount),1011(adb),1015(sdcard_rw),1028(sdcard_r),3001(net_bt_admin),3002(net_bt),3003(inet),3006(net_bw_stats)
[email protected]:/ # ls -la /system/bin/su
-rwsr-sr-x root shell 22364 2008-08-01 12:00 su
[email protected]:/ #
So the su binary is present and has setuid bit set on its permissions. But if I run it from a SSH session, or via a terminal emulator on the Tab itself, I get permission error:
[email protected]:/ $ su
Permission denied
1|[email protected]:/ $
Various root checking apps report similar problems. What am I doing wrong? Other threads suggest steps to recreate the su binary with the correct 6755 permissions, but as far as I can see, everything is already as it should be permissions-wise.
Thanks.
Wrong section. This here is only for Tab 1.
same problem
hanspampel said:
Wrong section. This here is only for Tab 1.
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I cannot find a better match for my situation than this. Any luck? Please link if your post was moved elsewhere.
jphilli85 said:
I cannot find a better match for my situation than this. Any luck? Please link if your post was moved elsewhere.
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Well, given the description (even though the OP was for the Gtab 2), I'd try the full path to the su binary.
If "ls -l /system/bin/su shows
-rwsr-sr-x root shell 22364 2008-08-01 12:00 su
then I would try
$ /system/bin/su
and see if it works - there may be another "su" on your $PATH.
If that's not it, then check that your user account has execute permissions to /system and /system/bin

DL701Q rooted, no apk, (digiland 7") need help backtracking how

Got root, then su binary installed need some help backtracking a few things. If someone is up for it?
I guess the first thing first is. The first time I adb shell'd I got promted with root user: ( does this happen right off the bat for anyone else? I did a few things before this with modstrings and busybox. But, didn't try adb till after)
Code:
adb shell
[email protected]:/ #
Once I noticed I had root on shell I simply found the system mount at /dev/ubui0_0 and I mounted it rw.
Code:
[email protected]:/ # mount -o remount, /dev/ubi0_0
moved the su binary over to the sdcard. wrote it to system/xbin link named to /system/bin. gave permisions.
Code:
adb push su /sdcard/
[email protected]:/ # cat /sdcard/su > /system/xbin/su
[email protected]:/ # ln -s /system/xbin/su
[email protected]:/ # chmod 6755 /system/xbin/su
[email protected]:/ # su
[email protected]:/ # :D
Off I went. I need to update the binary, but as of right now Superuser shows root as 'allow', SuperSU deny (think it old binary).
If you guys are not getting root after adb shell on this device, I think I can backtrack the modstrings and other stuff I did.
I really don't know where this device sits on getting rooted. It seems like some windows programs did it before an update that happened at some point, but not anymore? I don't have access to windows so I don't keep up with those methods.
Thanks! Hope someone can help me out.

[Q] I can't see sdcard contents with su. Why?

I'have rooted a Primux zeta 2 with Android 4.4.2. I can see what stuff is stored in my (internal/emulated) sdcard (/storage/sdcard0) and external one (/storage/sdcard1) using ls command in Terminal Emulator. But if I do su, I can't see it:
[email protected]:/ $ ls /storage/sdcard0/
Alarms
Android
....
[email protected]:/ $
[email protected]:/ $ su -
[email protected]:/ # ls /storage/sdcard0/
(empty)
[email protected]:/ #

How to get ADB shell with uid=0(root) on i9500?

Hi. I set following values in default.prop but have no adb root shell.
Code:
[email protected]:/ $ grep secure default.prop
ro.secure=0
ro.adb.secure=0
Code:
[email protected]:/ $ id
uid=2000(shell) gid=2000(shell) groups=1003(graphics),1004(input),1007(log),1011(adb),1015(sdcard_rw),1028(sdcard_r),3001(net_bt_admin),3002(net_bt),3003(inet),3006(net_bw_stats) context=u:r:shell:s0
I use factory boot and system partitions, except one change I made to default.prop.
Can anyone give any suggestions or pointers?
up
up
up

Problem with secure settings

Hi all,
im using a rooted samsung galaxy note 3 with lollipop
i have installed tasker to automate a few things ...
in addition i have installed the app "secure settings" to open the lookscreen
because of the message from secure settings in "System+ Module", that "Root access was not detected. The System+ module requires root access to function, i try the following:
Found on https://www.reddit.com/comments/3uf5bn ....
---------------------------------
adb shell
su
mount -o remount,rw /system
touch /sbin/su /system/bin/su /system/xbin/su
mount -o remount,ro /system
exit
reboot
---------------------------
im using Android Debug Bridge version 1.0.41
Version 28.0.3-5475833 <-- i think that's the latest version
C:\adb>adb shell
[email protected]:/ $ su
[email protected]:/ # mount -o remount,rw /system
[email protected]:/ # touch /sbin/su /system/bin/su /system/xbin/su
touch: usage: touch [-alm] [-t YYYYMMDD[.hhmmss]] <file>
1|[email protected]:/ # exit
1|[email protected]:/ $ exit
C:\adb>adb shell
[email protected]:/ $ su
[email protected]:/ # mount -o remount,rw /system
[email protected]:/ # touch /sbin/su /system/bin/su /system/xbin/su <-- don't work
touch: usage: touch [-alm] [-t YYYYMMDD[.hhmmss]] <file>
1|[email protected]:/ # exit
1|[email protected]:/ $ exit
C:\adb>adb shell
[email protected]:/ $ su
[email protected]:/ # touch /sbin/su <-- tried single step
255|[email protected]:/ # < -- is that the problem?
----------------------------
please help me ....
thanks Mikel

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