Fix following symlinks when processing the fixup list

The previous fix in b41daec was incomplete. Fixup entries are
given the original path without calling cleanup_pathname().
To make sure we don't follow a symlink, we must strip trailing
slashes from the path.

The fixup entries are always directories. Make sure we try to modify
only directories by providing O_DIRECTORY to open() (if supported)
and if it fails to check directory via lstat().

Fixes libarchive#1566

Author: mmatuska

libarchive/archive_write_disk_posix.c

@@ -2462,6 +2462,7 @@ _archive_write_disk_close(struct archive *_a)
 	struct archive_write_disk *a = (struct archive_write_disk *)_a;
 	struct fixup_entry *next, *p;
 	struct stat st;
+	char *c;
 	int fd, ret;
 
 	archive_check_magic(&a->archive, ARCHIVE_WRITE_DISK_MAGIC,
@@ -2475,24 +2476,49 @@ _archive_write_disk_close(struct archive *_a)
 	while (p != NULL) {
 		fd = -1;
 		a->pst = NULL; /* Mark stat cache as out-of-date. */
-		if (p->fixup &
-		    (TODO_TIMES | TODO_MODE_BASE | TODO_ACLS | TODO_FFLAGS)) {
-			fd = open(p->name,
-			    O_WRONLY | O_BINARY | O_NOFOLLOW | O_CLOEXEC);
+
+		/* We must strip trailing slashes from the path to avoid
+		   dereferencing symbolic links to directories */
+		c = p->name;
+		while (*c != '\0')
+			c++;
+		while (c != p->name && *(c - 1) == '/') {
+			c--;
+			*c = '\0';
+		}
+
+		if (p->fixup == 0)
+			goto skip_fixup_entry;
+		else {
+			fd = open(p->name, O_BINARY | O_NOFOLLOW | O_RDONLY
+#if defined(O_DIRECTORY)
+			    | O_DIRECTORY
+#endif
+			    | O_CLOEXEC);
+			/*
+		 `	 * If we don't support O_DIRECTORY,
+			 * or open() has failed, we must stat()
+			 * to verify that we are opening a directory
+			 */
+#if defined(O_DIRECTORY)
 			if (fd == -1) {
-				/* If we cannot lstat, skip entry */
-				if (lstat(p->name, &st) != 0)
+				if (lstat(p->name, &st) != 0 ||
+				    !S_ISDIR(st.st_mode)) {
 					goto skip_fixup_entry;
-				/*
-				 * If we deal with a symbolic link, mark
-				 * it in the fixup mode to ensure no
-				 * modifications are made to its target.
-				 */
-				if (S_ISLNK(st.st_mode)) {
-					p->mode &= ~S_IFMT;
-					p->mode |= S_IFLNK;
 				}
 			}
+#else
+#if HAVE_FSTAT
+			if (fd > 0 && (
+			    fstat(fd, &st) != 0 || !S_ISDIR(st.st_mode))) {
+				goto skip_fixup_entry;
+			} else
+#endif
+			if (lstat(p->name, &st) != 0 ||
+			    !S_ISDIR(st.st_mode)) {
+				goto skip_fixup_entry;
+			}
+#endif
 		}
 		if (p->fixup & TODO_TIMES) {
 			set_times(a, fd, p->mode, p->name,
@@ -2504,14 +2530,13 @@ _archive_write_disk_close(struct archive *_a)
 		if (p->fixup & TODO_MODE_BASE) {
 #ifdef HAVE_FCHMOD
 			if (fd >= 0)
-				fchmod(fd, p->mode);
+				fchmod(fd, p->mode & 07777);
 			else
 #endif
 #ifdef HAVE_LCHMOD
-			lchmod(p->name, p->mode);
+			lchmod(p->name, p->mode & 07777);
 #else
-			if (!S_ISLNK(p->mode))
-				chmod(p->name, p->mode);
+			chmod(p->name, p->mode & 07777);
 #endif
 		}
 		if (p->fixup & TODO_ACLS)
@@ -2664,7 +2689,6 @@ new_fixup(struct archive_write_disk *a, const char *pathname)
 	fe->next = a->fixup_list;
 	a->fixup_list = fe;
 	fe->fixup = 0;
-	fe->mode = 0;
 	fe->name = strdup(pathname);
 	return (fe);
 }

libarchive/test/test_write_disk_fixup.c

@@ -47,26 +47,50 @@ DEFINE_TEST(test_write_disk_fixup)
 	/*
 	 * Create a file
 	 */
-	assertMakeFile("victim", 0600, "a");
+	assertMakeFile("file", 0600, "a");
+
+	/*
+	 * Create a directory
+	 */
+	assertMakeDir("dir", 0700);
 
 	/*
 	 * Create a directory and a symlink with the same name
 	 */
 
-	/* Directory: dir */
+	/* Directory: dir1 */
+        assert((ae = archive_entry_new()) != NULL);
+        archive_entry_copy_pathname(ae, "dir1/");
+        archive_entry_set_mode(ae, AE_IFDIR | 0555);
+	assertEqualIntA(ad, 0, archive_write_header(ad, ae));
+	assertEqualIntA(ad, 0, archive_write_finish_entry(ad));
+        archive_entry_free(ae);
+
+	/* Directory: dir2 */
         assert((ae = archive_entry_new()) != NULL);
-        archive_entry_copy_pathname(ae, "dir");
-        archive_entry_set_mode(ae, AE_IFDIR | 0606);
+        archive_entry_copy_pathname(ae, "dir2/");
+        archive_entry_set_mode(ae, AE_IFDIR | 0555);
 	assertEqualIntA(ad, 0, archive_write_header(ad, ae));
 	assertEqualIntA(ad, 0, archive_write_finish_entry(ad));
         archive_entry_free(ae);
 
-	/* Symbolic Link: dir -> foo */
+	/* Symbolic Link: dir1 -> dir */
+	assert((ae = archive_entry_new()) != NULL);
+	archive_entry_copy_pathname(ae, "dir1");
+	archive_entry_set_mode(ae, AE_IFLNK | 0777);
+	archive_entry_set_size(ae, 0);
+	archive_entry_copy_symlink(ae, "dir");
+	assertEqualIntA(ad, 0, r = archive_write_header(ad, ae));
+	if (r >= ARCHIVE_WARN)
+		assertEqualIntA(ad, 0, archive_write_finish_entry(ad));
+	archive_entry_free(ae);
+
+	/* Symbolic Link: dir2 -> file */
 	assert((ae = archive_entry_new()) != NULL);
-	archive_entry_copy_pathname(ae, "dir");
+	archive_entry_copy_pathname(ae, "dir2");
 	archive_entry_set_mode(ae, AE_IFLNK | 0777);
 	archive_entry_set_size(ae, 0);
-	archive_entry_copy_symlink(ae, "victim");
+	archive_entry_copy_symlink(ae, "file");
 	assertEqualIntA(ad, 0, r = archive_write_header(ad, ae));
 	if (r >= ARCHIVE_WARN)
 		assertEqualIntA(ad, 0, archive_write_finish_entry(ad));
@@ -75,7 +99,9 @@ DEFINE_TEST(test_write_disk_fixup)
 	assertEqualInt(ARCHIVE_OK, archive_write_free(ad));
 
 	/* Test the entries on disk. */
-	assertIsSymlink("dir", "victim", 0);
-	assertFileMode("victim", 0600);
+	assertIsSymlink("dir1", "dir", 0);
+	assertIsSymlink("dir2", "file", 0);
+	assertFileMode("dir", 0700);
+	assertFileMode("file", 0600);
 #endif
 }