From: Timo Sirainen <timo.sirainen@dovecot.fi>
Date: Wed, 16 Nov 2016 09:40:35 +0000 (+0200)
Subject: lib: Add fd_close_maybe_stdio()
X-Git-Tag: 2.2.27~151
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=58bd9504a72311e5b8b6cd6c4ff1b20ef2ee6b9f;p=thirdparty%2Fdovecot%2Fcore.git

lib: Add fd_close_maybe_stdio()

The idea is that this should be used whenever closing fds that may be 0 or
1. If they are closed normally, the following code may end up using 0/1 fd
for other purposes, which could cause problems.
---

diff --git a/src/lib/lib.c b/src/lib/lib.c
index c1605cad8c..0b40fb1643 100644
--- a/src/lib/lib.c
+++ b/src/lib/lib.c
@@ -34,6 +34,25 @@ int close_keep_errno(int *fd)
 	return ret;
 }
 
+void fd_close_maybe_stdio(int *fd_in, int *fd_out)
+{
+	int *fdp[2] = { fd_in, fd_out };
+
+	if (*fd_in == *fd_out)
+		*fd_in = -1;
+
+	for (unsigned int i = 0; i < N_ELEMENTS(fdp); i++) {
+		if (*fdp[i] == -1)
+			;
+		else if (*fdp[i] > 1)
+			i_close_fd(fdp[i]);
+		else if (dup2(dev_null_fd, *fdp[i]) == *fdp[i])
+			*fdp[i] = -1;
+		else
+			i_fatal("dup2(/dev/null, %d) failed: %m", *fdp[i]);
+	}
+}
+
 #undef i_unlink
 int i_unlink(const char *path, const char *source_fname,
 	     unsigned int source_linenum)
diff --git a/src/lib/lib.h b/src/lib/lib.h
index 1581924759..fa386892ae 100644
--- a/src/lib/lib.h
+++ b/src/lib/lib.h
@@ -54,6 +54,10 @@ typedef void lib_atexit_callback_t(void);
 extern int dev_null_fd;
 
 int close_keep_errno(int *fd);
+/* Close fd_in and fd_out, unless they're already -1. They can point to the
+   same fd, in which case they're closed only once. If they point to stdin
+   or stdout, they're replaced with /dev/null. */
+void fd_close_maybe_stdio(int *fd_in, int *fd_out);
 /* Call unlink(). If it fails, log an error including the source filename
    and line number. */
 int i_unlink(const char *path, const char *source_fname,