Date: Fri, 29 Nov 2019 18:16:06 +0300 From: Dmitry Marakasov <amdmi3@amdmi3.ru> To: freebsd-stable@freebsd.org Subject: How can kill(-1, 0) return EPERM? Message-ID: <20191129151606.GD4071@hades.panopticon>
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Hi!
I'm helping to investigate some userspace issue [1], where kill(-1, SIGKILL)
fails with EPERM. I've managed to isolate this case in a small program:
```
#include <err.h>
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
int main() {
if (setuid(66) == -1) // uucp, just for the test
err(1, "setuid");
int res = kill(-1, 0); // <- fails with EPERM
fprintf(stderr, "kill(-1, 0) result=%d, errno=%s\n", res, strerror(errno));
return 0;
}
```
when run from root on 12.1 kill call fails with EPERM. However I cannot
comprehend what it is caused by and how it's even possible: kill(2) manpage
says that with pid=-1 kill should only send (and in this case of sig=0,
/not/ send) signals to the processes belonging to the current uid, so there
should be no permission problems. I've also looked into the kernel code
(sys_kill, killpg1), and it matches to what manpage says, I see no way
for it to return EPERM: sys_kill() should fall through to the switch, call
killpg1() with all=1 and killpg1() if(all) branch may only set `ret` to
either 0 or ESRCH. Am I missing something, or is there a problem somewhere?
[1] https://github.com/NixOS/nix/issues/3250
--
Dmitry Marakasov . 55B5 0596 FF1E 8D84 5F56 9510 D35A 80DD F9D2 F77D
amdmi3@amdmi3.ru ..: https://github.com/AMDmi3
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