main: fix daemonization stdio redirection and fd leak

Two bugs in the daemon child setup:

1. The condition `cur_fd > 0` fails to redirect stdin/stdout/stderr
   when open("/dev/null") returns fd 0 (possible if stdin was already
   closed before daemonising).  Change to `cur_fd >= 0` to handle
   that case correctly.

2. After the three dup2() calls the original file descriptor
   `cur_fd` is never closed.  If open() returned a descriptor number
   greater than 2 (the common case), that descriptor is leaked into
   the server process for its entire lifetime.  Add `close(cur_fd)`
   when `cur_fd > 2` to release it.

3. Change the open() flags from O_WRONLY to O_RDWR so that fd 0
   (stdin) is also opened in a readable state, matching normal daemon
   practice.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

1 files changed, 4 insertions, 2 deletions

diff --git a/main.c b/main.c
index fd065f6..c345add 100644
--- a/main.c
+++ b/main.c
@@ -642,11 +642,13 @@ int main(int argc, char **argv)
 			if (chdir("/"))
 				perror("chdir()");
 
-			cur_fd = open("/dev/null", O_WRONLY);
-			if (cur_fd > 0) {
+			cur_fd = open("/dev/null", O_RDWR);
+			if (cur_fd >= 0) {
 				dup2(cur_fd, 0);
 				dup2(cur_fd, 1);
 				dup2(cur_fd, 2);
+				if (cur_fd > 2)
+					close(cur_fd);
 			}
 
 			break;