Re: Why can setuid programs regain root after dropping it when using capabilities?

[Jan Engelhardt <jengelh@linux01.gwdg.de>]

>>While debugging some code, I found that a setuid program could regain
>>root after dropping root if the program used capabilities. (I tested
>>this on 2.6.14 and 2.6.9.) Is this the expected behavior? Here's a
>>short test case:
>>
>>/* chown root this program, suid it, and run it as non-root */
>>#include <sys/types.h>
>>#include <sys/capability.h>
>>#include <unistd.h>
>>#include <stdio.h>
>>int main() {
>>   cap_set_proc(cap_from_text("all-eip")); /* drop all caps */
>>   setuid(getuid());                       /* drop root. this call succeeds */
>>   setuid(0);                              /* this should fail! but doesn't */

uid != euid. You would probably have to use

  seteuid(getuid());

Plus there is also the feature of saved ids, see sys_setresuid().



Jan Engelhardt
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