From d3b16d78293ba0099cd435736b7a9fab2c2e0201 Mon Sep 17 00:00:00 2001
From: Frank Denis <github@pureftpd.org>
Date: Wed, 4 Nov 2015 02:18:19 +0100
Subject: [PATCH] Use writev() instead of writing before an allocated region

---
 generic/tcp_proto.c | 14 +++++++-------
 lib.h               | 15 +++++++++++++++
 2 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/generic/tcp_proto.c b/generic/tcp_proto.c
index 34b6e35..da99d3a 100644
--- a/generic/tcp_proto.c
+++ b/generic/tcp_proto.c
@@ -56,16 +56,16 @@
 
 int tcp_write(int fd, char *buf, int len)
 {
-     register char *ptr;
+     struct iovec iov[2];
+     uint16_t header;
 
-     /* \/ WHOEVER WROTE THAT IS A DANGEROUS PSYCHOPATH \/ */
-     ptr = buf - sizeof(short);
+     header = htons((uint16_t) len);
+     len  = len & VTUN_FSIZE_MASK;
 
-     *((unsigned short *)ptr) = htons(len); 
-     /* /\ WHOEVER WROTE THAT IS A DANGEROUS PSYCHOPATH /\ */
-     len  = (len & VTUN_FSIZE_MASK) + sizeof(short);
+     iov[0] = (struct iovec) { .iov_base = &header, .iov_len = 2U };
+     iov[1] = (struct iovec) { .iov_base = buf, .iov_len = len };
 
-     return write_n(fd, ptr, len);
+     return write_v(fd, iov, 2);
 }
 
 int tcp_read(int fd, char *buf)
diff --git a/lib.h b/lib.h
index b42eac0..c660be6 100644
--- a/lib.h
+++ b/lib.h
@@ -26,6 +26,7 @@
 #include <sys/types.h>
 #include <signal.h>
 #include <errno.h>
+#include <unistd.h>
 
 #ifdef HAVE_LIBUTIL_H
 #include <libutil.h>
@@ -104,4 +105,18 @@ static inline int write_n(int fd, char *buf, int len)
 
 	return t;
 }
+
+static inline int write_v(int fd, const struct iovec *iov, int iov_count)
+{
+    ssize_t w = -1;
+
+    while (!__io_canceled) {
+        if( (w = writev(fd, iov, iov_count)) < 0 ){
+            if( errno == EINTR || errno == EAGAIN )
+                continue;
+        }
+        break;
+    }
+    return (int) w;
+}
 #endif /* _VTUN_LIB_H */