Permission denied when opening files from Termux

Question

I have an issue with file permission in Termux.

For instance, I installed c4droid and copied the Termux /include and /lib folders content in the /c4droid folder where the headers are being looked for at compilation. I changed the owner and group to the correct name and mode to 777, but at compilation, it says "cannot open ****.h permission denied".

Same thing with a worldlist that comes from the SD card that I put on a folder meant to be used with hydra, not only have I have to use root access to unzip the file and move it around, but hydra itself can't open it.

What is this so important thing that I am missing about Termux and filed ownership and permissions?

Answer 1

The above comments hint toward SELinux blocking access to the files that are being copied around to the /data/data/ directory of apps. Yes, it is SELinux blocking the access, you just need to set it to permissive mode with SELinux_switch, and don't forget to set the user and group to the app's one.

So, copying the files from Termux with the option -pZL keeps everything in place, and once you set the correct owner and group, it will work. I have not tried having a symlink from the droidc's /includes and /libs folder to Termux's ones. If you missed fixing permission while copying files, you can use /system/bin/restorecon -R (recurse) one both /include and /lib folders.

Answer 2

TL;DR:

$su
#chown u0_a???:u0_a??? <files>
#restorecon -v <files>
#exit

or

$su
#chown -R u-a???:u0_a??? <directories>
#restorecon -vR <directories>
#exit

IMPORTANT: Commands run via sudo work differently from commands run from a root prompt via su. sudo ls -lZ ≠ su ls -lZ (which is unexpected and violates so many assumptions, but I assure you that it is nevertheless so. I assume there are a couple of other non-obvious ways these commands could fail, so I'd advise trying a couple of different ways to be root if this fails)

Make sure to get the correct username and group for your termux user via "ls -l" or similar, and use that username and group in the commands above.

I found this solution to fixing SElinux file permissions after copying from the SDcard back into my Termux home directory on a GitHub issue And it took me so much time and effort to dig up that I figured I repost it a couple of times to make it easier next time this "Why, no! you're not allowed to restore your backups!" bites my ass.

You can test to see if this is your problem before implementing this via ls -lZ. Compare to a file you can access to compare the SELinux security context of the two files and verify that they differ.