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Click here for more info. Hi everybody, i'd like to know what is the difference between the real uid and the effective uid if someone can point out a good source of information it would be enough, i've been googling but things are still confuse in my head.
Cheers, Milosevic. I think this is a pretty good summary: Quote:. Find More Posts by xjlittle View Blog. Thread Tools. After executing the setuid program, it will have your real id since you're the process owner and the effective user id of the file owner for example root since it is setuid. The program does whatever magic it needs to do with superuser privileges and then wants to do something on your behalf.
That means, attempting to do something that you shouldn't be able to do should fail. How does it do that? Well, obviously by changing its effective user id to the real user id!
Now that setuid program has no way of switching back since all the kernel knows is your id and Bang, you're dead.
Every process has an owner and belongs to a group. In our shell, every process that we'll now run will inherit the privileges of my user account and will run with the same UID and GID. You can see that the owner and the group of the file are root.
This is because the ping command needs to open up a socket and the Linux kernel demands root privilege for that. This is a special permission bit for specific binary executable files like ping and sudo which is known as setuid. The kernel makes the decision whether this process has the privilege by looking on the EUID of the process. Because now the EUID points to root , the operation won't be rejected by the kernel. Notice : On latest Linux releases the output of the ping command will look different because of the fact that they adopted the Linux Capabilities approach instead of this setuid approach - for those who are not familiar - read here.
The Saved user ID SUID is being used when a privileged process is running as root for example and it needs to do some unprivileged tasks. This is how I understand it. The file an user executes equivalent to starting a process will have a RUID equal to that user's id. Important thing to note here is that the uid which created a file is not the same as the uid that executes the file. They can be the same or different.
When a file has the setuid bit on it, whenever an uid executes that file, that uid will temporary be replaced with the file owner's uid. So, if we have a file owned by uid and has the setuid bit on it, whenever uid executes that file, that file will be executed with the uid How are we doing?
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