From: Lennart Poettering <lennart@poettering.net>
Date: Mon, 2 Oct 2017 08:51:19 +0000 (+0200)
Subject: path-util: some updates to path_make_relative()
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?a=commitdiff_plain;h=0b49a6ad440392bc8758db5dfd522287c80ee6a8;p=elogind.git

path-util: some updates to path_make_relative()

Don't miscount number of "../" to generate, if we "." is included in an
input path.

Also, refuse if we encounter "../" since we can't possibly follow that
up properly, without file system access.

Some other modernizations.
---

diff --git a/src/basic/path-util.c b/src/basic/path-util.c
index acd1007e3..280beae22 100644
--- a/src/basic/path-util.c
+++ b/src/basic/path-util.c
@@ -132,8 +132,7 @@ int path_make_relative(const char *from_dir, const char *to_path, char **_r) {
 
         /* Skip the common part. */
         for (;;) {
-                size_t a;
-                size_t b;
+                size_t a, b;
 
                 from_dir += strspn(from_dir, "/");
                 to_path += strspn(to_path, "/");
@@ -145,7 +144,6 @@ int path_make_relative(const char *from_dir, const char *to_path, char **_r) {
                         else
                                 /* from_dir is a parent directory of to_path. */
                                 r = strdup(to_path);
-
                         if (!r)
                                 return -ENOMEM;
 
@@ -176,21 +174,32 @@ int path_make_relative(const char *from_dir, const char *to_path, char **_r) {
 
         /* Count the number of necessary ".." elements. */
         for (n_parents = 0;;) {
+                size_t w;
+
                 from_dir += strspn(from_dir, "/");
 
                 if (!*from_dir)
                         break;
 
-                from_dir += strcspn(from_dir, "/");
-                n_parents++;
+                w = strcspn(from_dir, "/");
+
+                /* If this includes ".." we can't do a simple series of "..", refuse */
+                if (w == 2 && from_dir[0] == '.' && from_dir[1] == '.')
+                        return -EINVAL;
+
+                /* Count number of elements, except if they are "." */
+                if (w != 1 || from_dir[0] != '.')
+                        n_parents++;
+
+                from_dir += w;
         }
 
-        r = malloc(n_parents * 3 + strlen(to_path) + 1);
+        r = new(char, n_parents * 3 + strlen(to_path) + 1);
         if (!r)
                 return -ENOMEM;
 
-        for (p = r; n_parents > 0; n_parents--, p += 3)
-                memcpy(p, "../", 3);
+        for (p = r; n_parents > 0; n_parents--)
+                p = mempcpy(p, "../", 3);
 
         strcpy(p, to_path);
         path_kill_slashes(r);
diff --git a/src/test/test-path-util.c b/src/test/test-path-util.c
index 08d12d95b..5bfafce2d 100644
--- a/src/test/test-path-util.c
+++ b/src/test/test-path-util.c
@@ -262,6 +262,7 @@ static void test_make_relative(void) {
 
         assert_se(path_make_relative("some/relative/path", "/some/path", &result) < 0);
         assert_se(path_make_relative("/some/path", "some/relative/path", &result) < 0);
+        assert_se(path_make_relative("/some/dotdot/../path", "/some/path", &result) < 0);
 
 #define test(from_dir, to_path, expected) {                \
                 _cleanup_free_ char *z = NULL;             \
@@ -275,6 +276,7 @@ static void test_make_relative(void) {
         test("/some/path", "/some/path/in/subdir", "in/subdir");
         test("/some/path", "/", "../..");
         test("/some/path", "/some/other/path", "../other/path");
+        test("/some/path/./dot", "/some/further/path", "../../further/path");
         test("//extra/////slashes///won't////fool///anybody//", "////extra///slashes////are/just///fine///", "../../../are/just/fine");
 }
 #endif // 0