https://bugs.gentoo.org/948106

Backport provided by Red Hat on the VINCE case.
diff --git a/checksum.c b/checksum.c
index cb21882..66e8089 100644
--- a/checksum.c
+++ b/checksum.c
@@ -406,7 +406,7 @@ void file_checksum(const char *fname, const STRUCT_STAT *st_p, char *sum)
 	int32 remainder;
 	int fd;
 
-	fd = do_open(fname, O_RDONLY, 0);
+	fd = do_open_checklinks(fname);
 	if (fd == -1) {
 		memset(sum, 0, file_sum_len);
 		return;
diff --git a/flist.c b/flist.c
index 087f9da..1783253 100644
--- a/flist.c
+++ b/flist.c
@@ -1390,7 +1390,7 @@ struct file_struct *make_file(const char *fname, struct file_list *flist,
 
 	if (copy_devices && am_sender && IS_DEVICE(st.st_mode)) {
 		if (st.st_size == 0) {
-			int fd = do_open(fname, O_RDONLY, 0);
+			int fd = do_open_checklinks(fname);
 			if (fd >= 0) {
 				st.st_size = get_device_size(fd, fname);
 				close(fd);
diff --git a/generator.c b/generator.c
index 110db28..3f13bb9 100644
--- a/generator.c
+++ b/generator.c
@@ -1798,7 +1798,7 @@ static void recv_generator(char *fname, struct file_struct *file, int ndx,
 
 	if (write_devices && IS_DEVICE(sx.st.st_mode) && sx.st.st_size == 0) {
 		/* This early open into fd skips the regular open below. */
-		if ((fd = do_open(fnamecmp, O_RDONLY, 0)) >= 0)
+		if ((fd = do_open_nofollow(fnamecmp, O_RDONLY)) >= 0)
 			real_sx.st.st_size = sx.st.st_size = get_device_size(fd, fnamecmp);
 	}
 
@@ -1867,7 +1867,7 @@ static void recv_generator(char *fname, struct file_struct *file, int ndx,
 	}
 
 	/* open the file */
-	if (fd < 0 && (fd = do_open(fnamecmp, O_RDONLY, 0)) < 0) {
+	if (fd < 0 && (fd = do_open_checklinks(fnamecmp)) < 0) {
 		rsyserr(FERROR, errno, "failed to open %s, continuing",
 			full_fname(fnamecmp));
 	  pretend_missing:
diff --git a/receiver.c b/receiver.c
index 8031b8f..edfbb21 100644
--- a/receiver.c
+++ b/receiver.c
@@ -775,7 +775,7 @@ int recv_files(int f_in, int f_out, char *local_name)
 			if (fnamecmp != fname) {
 				fnamecmp = fname;
 				fnamecmp_type = FNAMECMP_FNAME;
-				fd1 = do_open(fnamecmp, O_RDONLY, 0);
+				fd1 = do_open_nofollow(fnamecmp, O_RDONLY);
 			}
 
 			if (fd1 == -1 && basis_dir[0]) {
diff --git a/sender.c b/sender.c
index 2bbff2f..a4d46c3 100644
--- a/sender.c
+++ b/sender.c
@@ -350,7 +350,7 @@ void send_files(int f_in, int f_out)
 			exit_cleanup(RERR_PROTOCOL);
 		}
 
-		fd = do_open(fname, O_RDONLY, 0);
+		fd = do_open_checklinks(fname);
 		if (fd == -1) {
 			if (errno == ENOENT) {
 				enum logcode c = am_daemon && protocol_version < 28 ? FERROR : FWARNING;
diff --git a/syscall.c b/syscall.c
index 47c5ea5..c55ae5f 100644
--- a/syscall.c
+++ b/syscall.c
@@ -45,6 +45,8 @@ extern int preallocate_files;
 extern int preserve_perms;
 extern int preserve_executability;
 extern int open_noatime;
+extern int copy_links;
+extern int copy_unsafe_links;
 
 #ifndef S_BLKSIZE
 # if defined hpux || defined __hpux__ || defined __hpux
@@ -793,3 +795,21 @@ cleanup:
 	return retfd;
 #endif // O_NOFOLLOW, O_DIRECTORY
 }
+
+/*
+  varient of do_open/do_open_nofollow which does do_open() if the
+  copy_links or copy_unsafe_links options are set and does
+  do_open_nofollow() otherwise
+
+  This is used to prevent a race condition where an attacker could be
+  switching a file between being a symlink and being a normal file
+
+  The open is always done with O_RDONLY flags
+ */
+int do_open_checklinks(const char *pathname)
+{
+	if (copy_links || copy_unsafe_links) {
+		return do_open(pathname, O_RDONLY, 0);
+	}
+	return do_open_nofollow(pathname, O_RDONLY);
+}
diff --git a/t_unsafe.c b/t_unsafe.c
index 010cac5..e10619a 100644
--- a/t_unsafe.c
+++ b/t_unsafe.c
@@ -28,6 +28,9 @@ int am_root = 0;
 int am_sender = 1;
 int read_only = 0;
 int list_only = 0;
+int copy_links = 0;
+int copy_unsafe_links = 0;
+
 short info_levels[COUNT_INFO], debug_levels[COUNT_DEBUG];
 
 int
diff --git a/tls.c b/tls.c
index e6b0708..858f8f1 100644
--- a/tls.c
+++ b/tls.c
@@ -49,6 +49,9 @@ int list_only = 0;
 int link_times = 0;
 int link_owner = 0;
 int nsec_times = 0;
+int safe_symlinks = 0;
+int copy_links = 0;
+int copy_unsafe_links = 0;
 
 #ifdef SUPPORT_XATTRS
 
diff --git a/trimslash.c b/trimslash.c
index 1ec928c..f2774cd 100644
--- a/trimslash.c
+++ b/trimslash.c
@@ -26,6 +26,8 @@ int am_root = 0;
 int am_sender = 1;
 int read_only = 1;
 int list_only = 0;
+int copy_links = 0;
+int copy_unsafe_links = 0;
 
 int
 main(int argc, char **argv)
diff --git a/util1.c b/util1.c
index f260d39..d84bc41 100644
--- a/util1.c
+++ b/util1.c
@@ -365,7 +365,7 @@ int copy_file(const char *source, const char *dest, int tmpfilefd, mode_t mode)
 	int len;   /* Number of bytes read into `buf'. */
 	OFF_T prealloc_len = 0, offset = 0;
 
-	if ((ifd = do_open(source, O_RDONLY, 0)) < 0) {
+	if ((ifd = do_open_nofollow(source, O_RDONLY)) < 0) {
 		int save_errno = errno;
 		rsyserr(FERROR_XFER, errno, "open %s", full_fname(source));
 		errno = save_errno;