unix - Why do I need setuid(0) within a setuid-root C program that calls an administrative program with system()? -

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I had to hack some dirty Linux for someone, so that they could have a printer with cupsenable printoname Shell command while being a non root user I did not want to fully use the cuplessable syntax as the root, so I have written a cover which is in the input < Code> argv [1] system . .

I have created the program setuid root, but still, cuplessable failed "permission denied" and then I had a setuid (0) Code> system () and, take it and see, it worked.

The best way to give users control over the printer is probably a better way for me to be interested in chmod u + s vs setuid (0) There are complications of versus system () . Why did this happen?

to man system :

Do not use system () from a program with set-user-id or set-group-id privilege, because the strange values ​​of some environment variables can be used to break the mechanism Integrity Instead of the exec (3) family of tasks, but use execlp (3) or execvp (3) . Actually, those systems will not work properly with programs with set-user-id or set-group-id privileges, on which / bin / sh Bash is version 2, as Bash 2 leaves the privileges at startup.

and man bash from:

If the shell starts with effective user (group) id actual user (group) Id is not equal, and the -p option is not provided, no startup file is read, shell functions are not inherited from the environment; shellopts variable, If it appears in the environment, it is ignored, and the effective user id is real User ID is set.

This your Setuide (0) calls circumvented security.


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