From 1300f91149bf8477ec1b55ea0bd2ac6010f7b807 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Mon, 26 Nov 2018 15:52:33 +0100
Subject: [PATCH] rlimit: add new rlimit_nofile_safe() helper

This helper sets RLIMIT_NOFILE's soft limit to 1024 (FD_SETSIZE) for
compatibility with apps using select().

The idea is that we use this helper to reset the limit whenever we
invoke foreign code from our own processes which have bumped
RLIMIT_NOFILE high.
---
 src/shared/rlimit-util.c | 19 +++++++++++++++++++
 src/shared/rlimit-util.h |  1 +
 2 files changed, 20 insertions(+)

diff --git a/src/shared/rlimit-util.c b/src/shared/rlimit-util.c
index c133f84b7e9..74b3a023f18 100644
--- a/src/shared/rlimit-util.c
+++ b/src/shared/rlimit-util.c
@@ -389,3 +389,22 @@ int rlimit_nofile_bump(int limit) {
 
         return 0;
 }
+
+int rlimit_nofile_safe(void) {
+        struct rlimit rl;
+
+        /* Resets RLIMIT_NOFILE's soft limit FD_SETSIZE (i.e. 1024), for compatibility with software still using
+         * select() */
+
+        if (getrlimit(RLIMIT_NOFILE, &rl) < 0)
+                return log_debug_errno(errno, "Failed to query RLIMIT_NOFILE: %m");
+
+        if (rl.rlim_cur <= FD_SETSIZE)
+                return 0;
+
+        rl.rlim_cur = FD_SETSIZE;
+        if (setrlimit(RLIMIT_NOFILE, &rl) < 0)
+                return log_debug_errno(errno, "Failed to lower RLIMIT_NOFILE's soft limit to " RLIM_FMT ": %m", rl.rlim_cur);
+
+        return 1;
+}
diff --git a/src/shared/rlimit-util.h b/src/shared/rlimit-util.h
index 6139af3ff50..d4fca2b8556 100644
--- a/src/shared/rlimit-util.h
+++ b/src/shared/rlimit-util.h
@@ -22,3 +22,4 @@ void rlimit_free_all(struct rlimit **rl);
 #define RLIMIT_MAKE_CONST(lim) ((struct rlimit) { lim, lim })
 
 int rlimit_nofile_bump(int limit);
+int rlimit_nofile_safe(void);
-- 
2.47.3