fs-util: add new CHASE_NON_EXISTING flag to chase_symlinks()

This new flag controls whether to consider a problem if the referenced path
doesn't actually exist. If specified it's OK if the final file doesn't exist.

Note that this permits one or more final components of the path not to exist,
but these must not contain "../" for safety reasons (or, to be extra safe,
neither "./" and a couple of others, i.e. what path_is_safe() permits).

This new flag is useful when resolving paths before issuing an mkdir() or
open(O_CREAT) on a path, as it permits that the file or directory is created
later.

The return code of chase_symlinks() is changed to return 1 if the file exists,
and 0 if it doesn't. The latter is only returned in case CHASE_NON_EXISTING is
set.

1 files changed, 45 insertions, 11 deletions

diff --git a/src/test/test-fs-util.c b/src/test/test-fs-util.c
index fac3a1d089..2570bc5859 100644
--- a/src/test/test-fs-util.c
+++ b/src/test/test-fs-util.c
@@ -63,7 +63,7 @@ static void test_chase_symlinks(void) {
         /* Paths that use symlinks underneath the "root" */
 
         r = chase_symlinks(p, NULL, 0, &result);
-        assert_se(r >= 0);
+        assert_se(r > 0);
         assert_se(path_equal(result, "/usr"));
 
         result = mfree(result);
@@ -71,10 +71,15 @@ static void test_chase_symlinks(void) {
         assert_se(r == -ENOENT);
 
         q = strjoina(temp, "/usr");
+
+        r = chase_symlinks(p, temp, CHASE_NON_EXISTING, &result);
+        assert_se(r == 0);
+        assert_se(path_equal(result, q));
+
         assert_se(mkdir(q, 0700) >= 0);
 
         r = chase_symlinks(p, temp, 0, &result);
-        assert_se(r >= 0);
+        assert_se(r > 0);
         assert_se(path_equal(result, q));
 
         p = strjoina(temp, "/slash");
@@ -82,12 +87,12 @@ static void test_chase_symlinks(void) {
 
         result = mfree(result);
         r = chase_symlinks(p, NULL, 0, &result);
-        assert_se(r >= 0);
+        assert_se(r > 0);
         assert_se(path_equal(result, "/"));
 
         result = mfree(result);
         r = chase_symlinks(p, temp, 0, &result);
-        assert_se(r >= 0);
+        assert_se(r > 0);
         assert_se(path_equal(result, temp));
 
         /* Paths that would "escape" outside of the "root" */
@@ -97,21 +102,21 @@ static void test_chase_symlinks(void) {
 
         result = mfree(result);
         r = chase_symlinks(p, temp, 0, &result);
-        assert_se(r == 0 && path_equal(result, temp));
+        assert_se(r > 0 && path_equal(result, temp));
 
         p = strjoina(temp, "/6dotsusr");
         assert_se(symlink("../../../usr", p) >= 0);
 
         result = mfree(result);
         r = chase_symlinks(p, temp, 0, &result);
-        assert_se(r == 0 && path_equal(result, q));
+        assert_se(r > 0 && path_equal(result, q));
 
         p = strjoina(temp, "/top/8dotsusr");
         assert_se(symlink("../../../../usr", p) >= 0);
 
         result = mfree(result);
         r = chase_symlinks(p, temp, 0, &result);
-        assert_se(r == 0 && path_equal(result, q));
+        assert_se(r > 0 && path_equal(result, q));
 
         /* Paths that contain repeated slashes */
 
@@ -120,24 +125,24 @@ static void test_chase_symlinks(void) {
 
         result = mfree(result);
         r = chase_symlinks(p, NULL, 0, &result);
-        assert_se(r >= 0);
+        assert_se(r > 0);
         assert_se(path_equal(result, "/usr"));
 
         result = mfree(result);
         r = chase_symlinks(p, temp, 0, &result);
-        assert_se(r >= 0);
+        assert_se(r > 0);
         assert_se(path_equal(result, q));
 
         /* Paths using . */
 
         result = mfree(result);
         r = chase_symlinks("/etc/./.././", NULL, 0, &result);
-        assert_se(r >= 0);
+        assert_se(r > 0);
         assert_se(path_equal(result, "/"));
 
         result = mfree(result);
         r = chase_symlinks("/etc/./.././", "/etc", 0, &result);
-        assert_se(r == 0 && path_equal(result, "/etc"));
+        assert_se(r > 0 && path_equal(result, "/etc"));
 
         result = mfree(result);
         r = chase_symlinks("/etc/machine-id/foo", NULL, 0, &result);
@@ -151,6 +156,35 @@ static void test_chase_symlinks(void) {
         r = chase_symlinks(p, NULL, 0, &result);
         assert_se(r == -ELOOP);
 
+        /* Path which doesn't exist */
+
+        p = strjoina(temp, "/idontexist");
+        r = chase_symlinks(p, NULL, 0, &result);
+        assert_se(r == -ENOENT);
+
+        r = chase_symlinks(p, NULL, CHASE_NON_EXISTING, &result);
+        assert_se(r == 0);
+        assert_se(path_equal(result, p));
+        result = mfree(result);
+
+        p = strjoina(temp, "/idontexist/meneither");
+        r = chase_symlinks(p, NULL, 0, &result);
+        assert_se(r == -ENOENT);
+
+        r = chase_symlinks(p, NULL, CHASE_NON_EXISTING, &result);
+        assert_se(r == 0);
+        assert_se(path_equal(result, p));
+        result = mfree(result);
+
+        /* Path which doesn't exist, but contains weird stuff */
+
+        p = strjoina(temp, "/idontexist/..");
+        r = chase_symlinks(p, NULL, 0, &result);
+        assert_se(r == -ENOENT);
+
+        r = chase_symlinks(p, NULL, CHASE_NON_EXISTING, &result);
+        assert_se(r == -ENOENT);
+
         assert_se(rm_rf(temp, REMOVE_ROOT|REMOVE_PHYSICAL) >= 0);
 }