From 7c112351d9e941567e64063638396259546d9a48 Mon Sep 17 00:00:00 2001 From: Alyssa Ross Date: Sun, 7 Feb 2021 13:56:50 +0000 Subject: [PATCH] libutil: EPERM from kill(-1, ...) is fine I tested a trivial program that called kill(-1, SIGKILL), which was run as the only process for an unpriveleged user, on Linux and FreeBSD. On Linux, kill reported success, while on FreeBSD it failed with EPERM. POSIX says: > If pid is -1, sig shall be sent to all processes (excluding an > unspecified set of system processes) for which the process has > permission to send that signal. and > The kill() function is successful if the process has permission to > send sig to any of the processes specified by pid. If kill() fails, > no signal shall be sent. and > [EPERM] > The process does not have permission to send the signal to any > receiving process. My reading of this is that kill(-1, ...) may fail with EPERM when there are no other processes to kill (since the current process is ignored). Since kill(-1, ...) only attempts to kill processes the user has permission to kill, it can't mean that we tried to do something we didn't have permission to kill, so it should be fine to interpret EPERM the same as success here for any POSIX-compliant system. This fixes an issue that Mic92 encountered[1] when he tried to review a Nixpkgs PR on FreeBSD. [1]: https://github.com/NixOS/nixpkgs/pull/81459#issuecomment-606073668 --- src/libutil/util.cc | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/libutil/util.cc b/src/libutil/util.cc index 89f7b58f8..ef37275ac 100644 --- a/src/libutil/util.cc +++ b/src/libutil/util.cc @@ -946,7 +946,7 @@ void killUser(uid_t uid) #else if (kill(-1, SIGKILL) == 0) break; #endif - if (errno == ESRCH) break; /* no more processes */ + if (errno == ESRCH || errno == EPERM) break; /* no more processes */ if (errno != EINTR) throw SysError("cannot kill processes for uid '%1%'", uid); }