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Is is possible to change root's password using setuid?

What I tried is writing a simple program which calls system("passwd root") owned by root and its setuid bit is set but it didn't work. The output is: You may not view or modify password information for root.

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In your program, you probably overlooked making the real and effective uid set to the same value. Gids also should match root's gid. Something like this:

setuid(geteuid());
setgid(getegid());

See for example sue (a simple setuid/setgid wrapper).

  • Might he also need to set USER environment variable? – Otheus Feb 6 '16 at 17:49
  • He might - and LOGNAME - but the lack of proper permissions is the most likely problem. – Thomas Dickey Feb 6 '16 at 20:22
  • OK, after some testing, I found only setuid(geteuid()) is need. Interestingly enough, running the program via ltrace or strace prevented seteuid from happening, so those traces were bogus. – Otheus Feb 6 '16 at 22:19
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Thomas Dickey is absolutely right. However, don't do this. Use sudo instead.

Create /etc/sudoers.d/change_root_pass

YOURUSERNAME ALL = (ALL) passwd root

(Change YOURUSERNAME).

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