init: clamp fd limits to int

When setting the fd limit to 1 >> 31, the node fails to start:

ulimit -n 214748364
build/bin/bitcoind
Error: Not enough file descriptors available. -2147483648 available, 160 required.

Similar to the previous commit, this is fixed by capping the limit
to std::numeric_limits<int>::max().

Co-authored-by: Luke Dashjr <luke-jr+git@utopios.org>

src/util/fs_helpers.cpp

@@ -179,11 +179,13 @@ int RaiseFileDescriptorLimit(int min_fd)
         // Check the (possibly raised) current soft limit against the special
         // value of RLIM_INFINITY. Some platforms implement this as the maximum
         // uint64, others as int64 (-1). Avoid casting even if the return type
-        // is changed to uint64_t.
-        if (limitFD.rlim_cur == RLIM_INFINITY) {
+        // is changed to uint64_t. We also cap unlikely but possible values
+        // that would overflow int.
+        if (limitFD.rlim_cur == RLIM_INFINITY ||
+            std::cmp_greater_equal(limitFD.rlim_cur, std::numeric_limits<int>::max())) {
             return std::numeric_limits<int>::max();
         }
-        return limitFD.rlim_cur;
+        return static_cast<int>(limitFD.rlim_cur);
     }
     return min_fd; // getrlimit failed, assume it's fine
 #endif

test/functional/feature_init.py

@@ -348,6 +348,15 @@ class InitTest(BitcoinTestFramework):
         self.log.info("Testing node startup with RLIM_INFINITY fd limit")
         self.restart_node_with_fd_limit(self.RLIM_INFINITY)
 
+    def init_rlimit_large_test(self):
+        """Test that bitcoind starts correctly when the soft RLIMIT_NOFILE limit is above INT_MAX."""
+        if self.RLIM_INFINITY is None:
+            self.log.info("Skipping: resource module not available")
+            return
+
+        self.log.info("Testing node startup with fd limit above INT_MAX")
+        self.restart_node_with_fd_limit(1 << 31)
+
     def run_test(self):
         self.init_pid_test()
         self.init_stress_test_interrupt()
@@ -355,6 +364,7 @@ class InitTest(BitcoinTestFramework):
         self.break_wait_test()
         self.init_empty_test()
         self.init_rlimit_test()
+        self.init_rlimit_large_test()
 
 
 if __name__ == '__main__':