Honor the symbolic link option when copying files

Inspect source links without following them when COPYFILE_SYM is requested, before rejecting directories. This makes the documented option recreate link text instead of copying the referent, including dangling and directory links. Preserve requested link timestamps and report link-creation errors without overwriting the destination. Cover direct calls, destination directories, normal dereferencing and the existing rsync file caller.

src/copyfile.c

@@ -157,7 +157,13 @@ ssize_t copyfile(const char *src, const char *dst, int len, int opt)
 	if (!buffer)
 		return 0;
 
-	if (fisdir(src)) {
+	if (sym ? lstat(src, &st) : stat(src, &st)) {
+		saved_errno = errno;
+		size = -1;
+		goto exit;
+	}
+
+	if (S_ISDIR(st.st_mode)) {
 		saved_errno = EISDIR;	/* Error: source is a directory */
 		goto exit;
 	}
@@ -165,13 +171,7 @@ ssize_t copyfile(const char *src, const char *dst, int len, int opt)
 	/* Check if target is a directory, then append src filename. */
 	isdir = adjust_target(src, &dest);
 
-	/* Check if the source file is a symlink ... */
+	/* Only try readlink() if symlink and @sym is set. */
-	if (stat(src, &st)) {
-		size = -1;
-		goto exit;
-	}
-
-	/* ... only try readlink() if symlink and @sym is set. */
 	if (sym && (st.st_mode & S_IFMT) == S_IFLNK) {
 		size = readlink(src, buffer, BUFSIZ);
 		if (size > 0) {
@@ -181,8 +181,16 @@ ssize_t copyfile(const char *src, const char *dst, int len, int opt)
 			} else {
 				buffer[size] = 0;
 				size = !symlink(buffer, dest);
+				if (!size)
+					saved_errno = errno;
+				else if (keep_mtim) {
+					struct timespec tv[2] = { st.st_atim, st.st_mtim };
+
+					utimensat(AT_FDCWD, dest, tv, AT_SYMLINK_NOFOLLOW);
+				}
 			}
-		}
+		} else
+			saved_errno = errno;
 
 		/* Don't fall back to copy, that is a potentially
 		 * dangerous race condition, see CWE-367. */

src/rsync.c

@@ -24,6 +24,7 @@
 
 #include <errno.h>
 #include <fcntl.h>	/* AT_* macros */
+#include <libgen.h>	/* dirname() */
 #include <stdlib.h>	/* NULL, free() */
 #include <string.h>	/* strlen() */
 #include <strings.h>	/* rindex() */
@@ -159,15 +160,49 @@ int rsync(char *src, char *dst, int opt, int (*filter)(const char *file))
 
 static int copy(char *src, char *dst, int opt)
 {
+	char *dest = NULL, *temp = NULL, *file = NULL;
+	int result = 1, saved_errno, made_temp = 0;
+
 	copyfile(src, dst, 0, opt | LITE_FOPT_COPYFILE_SYM);
-	if (errno) {
+	if (errno != EEXIST)
-		if (errno != EEXIST)
+		return errno ? 1 : 0;
+
+	/* Replace an existing destination only after the new link is ready. */
+	if (fisdir(dst)) {
+		char *base = strrchr(src, '/');
+
+		if (asprintf(&dest, "%s%s%s", dst, fisslashdir(dst) ? "" : "/", base ? base + 1 : src) < 0)
+			return 1;
+	} else {
+		dest = strdup(dst);
+		if (!dest)
 			return 1;
-
-		errno = 0;
 	}
+	if (asprintf(&temp, "%s/.rsync-XXXXXX", dirname(strdupa(dest))) < 0)
+		goto exit;
+	if (!mkdtemp(temp))
+		goto exit;
+	made_temp = 1;
+	if (asprintf(&file, "%s/link", temp) < 0)
+		goto exit;
 
-	return 0;
+	copyfile(src, file, 0, opt | LITE_FOPT_COPYFILE_SYM);
+	if (errno)
+		goto exit;
+	result = rename(file, dest) != 0;
+
+exit:
+	saved_errno = errno;
+	if (file)
+		unlink(file);
+	if (made_temp)
+		rmdir(temp);
+	free(file);
+	free(temp);
+	free(dest);
+	errno = saved_errno;
+
+	return result;
 }
 
 /* Creates dir/name @mode ... skipping / if dir already ends so. */

test/.gitignore

@@ -5,6 +5,7 @@
 /chomp
 /copyfile
 /fcopyfile
+/copyfile-symlink
 /dir
 /fexist
 /fisdir

test/Makefile.am

@@ -20,6 +20,7 @@ TESTS           =
 TESTS          += chomp
 TESTS          += copyfile
 TESTS          += fcopyfile
+TESTS          += copyfile-symlink
 TESTS          += dir
 TESTS          += fexist
 TESTS          += fisdir
@@ -41,3 +42,4 @@ TESTS          += which
 TESTS          += yorn
 
 check_PROGRAMS  = $(TESTS)
+copyfile_symlink_SOURCES = copyfile-symlink.c

test/copyfile-symlink.c

@@ -0,0 +1,114 @@
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include "check.h"
+
+static void check_link(const char *path, const char *target)
+{
+	char buf[256];
+	struct stat st;
+	ssize_t len;
+
+	fail_unless(lstat(path, &st) == 0 && S_ISLNK(st.st_mode));
+	len = readlink(path, buf, sizeof(buf));
+	fail_unless(len == (ssize_t)strlen(target));
+	fail_unless(memcmp(buf, target, len) == 0);
+}
+
+int main(void)
+{
+	char tmp[] = "/tmp/libite-copylink-XXXXXX";
+	const char payload[] = "target contents";
+	char buf[sizeof(payload)];
+	const char *targets[] = { "file", "dir", "missing", ".", "link" };
+	struct timespec times[2] = { { 1234567800, 0 }, { 1234567801, 0 } };
+	struct stat src_st, dst_st;
+	char cwd[4096];
+	size_t i;
+	FILE *fp;
+
+	fail_unless(getcwd(cwd, sizeof(cwd)) && mkdtemp(tmp));
+	fail_unless(chdir(tmp) == 0);
+	fail_unless(mkdir("dir", 0700) == 0);
+	fail_unless(mkdir("out", 0700) == 0);
+	fp = fopen("file", "w");
+	fail_unless(fp && fwrite(payload, 1, sizeof(payload), fp) == sizeof(payload));
+	fail_unless(fclose(fp) == 0);
+
+	for (i = 0; i < NELEMS(targets); i++) {
+		fail_unless(symlink(targets[i], "link") == 0);
+		fail_unless(copyfile("link", "copied", 0, LITE_FOPT_COPYFILE_SYM) == 1);
+		check_link("copied", targets[i]);
+		fail_unless(copyfile("link", "out", 0, LITE_FOPT_COPYFILE_SYM) == 1);
+		check_link("out/link", targets[i]);
+		/* Existing targets must survive a failed symlink creation. */
+		errno = 0;
+		fail_unless(copyfile("link", "file", 0, LITE_FOPT_COPYFILE_SYM) == 0);
+		fail_unless(errno == EEXIST);
+		check_link("copied", targets[i]);
+		fail_unless(unlink("copied") == 0 && unlink("out/link") == 0);
+		fail_unless(unlink("link") == 0);
+	}
+
+	fail_unless(symlink("file", "link") == 0);
+	/* Without SYM, continue to copy target data and preserve regular-file metadata. */
+	fail_unless(copyfile("link", "copied", 0, LITE_FOPT_KEEP_MTIME) == sizeof(payload));
+	fail_unless(lstat("copied", &dst_st) == 0 && S_ISREG(dst_st.st_mode));
+	fail_unless(stat("file", &src_st) == 0 && src_st.st_mtime == dst_st.st_mtime);
+	fp = fopen("copied", "r");
+	fail_unless(fp && fread(buf, 1, sizeof(buf), fp) == sizeof(payload));
+	fail_unless(memcmp(buf, payload, sizeof(payload)) == 0 && fclose(fp) == 0);
+	fail_unless(unlink("copied") == 0);
+
+	fail_unless(utimensat(AT_FDCWD, "link", times, AT_SYMLINK_NOFOLLOW) == 0);
+	fail_unless(copyfile("link", "copied", 0, LITE_FOPT_COPYFILE_SYM | LITE_FOPT_KEEP_MTIME) == 1);
+	check_link("copied", "file");
+	fail_unless(lstat("copied", &dst_st) == 0 && dst_st.st_mtime == times[1].tv_sec);
+	fail_unless(unlink("copied") == 0);
+	/* Exercise the existing rsync file caller, which requests SYM. */
+	fail_unless(rsync("link", "copied", 0, NULL) == 0);
+	check_link("copied", "file");
+	/* Reuse the destination after changing the source link. */
+	fail_unless(unlink("link") == 0 && symlink("file", "link") == 0);
+	fail_unless(rsync("link", "out", 0, NULL) == 0);
+	check_link("out/link", "file");
+	fail_unless(unlink("link") == 0 && symlink("copied", "link") == 0);
+	fail_unless(rsync("link", "out", 0, NULL) == 0);
+	check_link("out/link", "copied");
+	/* A same-path copy must not unlink its source. */
+	fail_unless(rsync("link", "link", 0, NULL) == 0);
+	check_link("link", "copied");
+	fail_unless(unlink("out/link") == 0);
+	/* Replacing a regular destination must also retain the source link. */
+	fail_unless(touch("out/link") == 0);
+	fail_unless(rsync("link", "out", 0, NULL) == 0);
+	check_link("out/link", "copied");
+	fail_unless(unlink("out/link") == 0);
+	/* A failed replacement must keep both the destination and source. */
+	fail_unless(mkdir("out/link", 0700) == 0);
+	fail_unless(touch("out/link/keep") == 0);
+	fail_unless(rsync("link", "out", 0, NULL) != 0);
+	fail_unless(fexist("out/link/keep"));
+	check_link("link", "copied");
+	fail_unless(unlink("out/link/keep") == 0 && rmdir("out/link") == 0);
+	if (getuid() != 0) {
+		fail_unless(mkdir("protected", 0700) == 0);
+		fail_unless(symlink("original", "protected/link") == 0);
+		fail_unless(chmod("protected", 0500) == 0);
+		fail_unless(rsync("link", "protected", 0, NULL) != 0);
+		check_link("protected/link", "original");
+		check_link("link", "copied");
+		fail_unless(chmod("protected", 0700) == 0);
+		fail_unless(unlink("protected/link") == 0 && rmdir("protected") == 0);
+	}
+	fail_unless(unlink("copied") == 0 && unlink("link") == 0);
+
+	errno = 0;
+	fail_unless(copyfile("dir", "copied", 0, LITE_FOPT_COPYFILE_SYM) == 0 && errno == EISDIR);
+	errno = 0;
+	fail_unless(copyfile("missing", "copied", 0, LITE_FOPT_COPYFILE_SYM) == -1 && errno == ENOENT);
+
+	fail_unless(unlink("file") == 0 && rmdir("dir") == 0 && rmdir("out") == 0);
+	fail_unless(chdir(cwd) == 0 && rmdir(tmp) == 0);
+	return 0;
+}