RFR: 8062795: (fs) Files.setPermissions requires read access when NOFOLLOW_LINKS specified [v2]

[Alan Bateman]

On Thu, 10 Aug 2023 00:40:00 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

>> If setting POSIX permissions while not following links fails with `AccessDeniedException` but the path does not contain any symbolic links, then retry the operation as if the `NOFOLLOW_LINKS` option had not been specified.
>
> Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8062795: Add missing bug ID to test

I don't think this is the right thing as it may do the wrong thing when there are concurrency changes on the file system. I think the simplest is to just attempt to open the file for write access, this should work for regular files.

Not tested, but I expect something like this is what you want here.


diff --git a/src/java.base/unix/classes/sun/nio/fs/UnixFileAttributeViews.java b/src/java.base/unix/classes/sun/nio/fs/UnixFileAttributeViews.java
index f35541a9e19..bcab5319d8d 100644
--- a/src/java.base/unix/classes/sun/nio/fs/UnixFileAttributeViews.java
+++ b/src/java.base/unix/classes/sun/nio/fs/UnixFileAttributeViews.java
@@ -31,6 +31,7 @@ import java.util.*;
 import java.util.concurrent.TimeUnit;
 import java.io.IOException;
 
+import static sun.nio.fs.UnixConstants.*;
 import static sun.nio.fs.UnixNativeDispatcher.*;
 
 class UnixFileAttributeViews {
@@ -262,20 +263,45 @@ class UnixFileAttributeViews {
         // chmod
         final void setMode(int mode) throws IOException {
             checkWriteExtended();
-            try {
-                if (followLinks) {
+
+            if (followLinks) {
+                try {
                     chmod(file, mode);
-                } else {
-                    int fd = file.openForAttributeAccess(false);
+                } catch (UnixException e) {
+                    e.rethrowAsIOException(file);
+                }
+                return;
+            }
+
+            if (O_NOFOLLOW == 0) {
+                throw new IOException("NOFOLLOW_LINKS is not supported on this platform");
+            }
+
+            int fd = -1;
+            try {
+                fd = open(file, O_RDONLY, O_NOFOLLOW);
+            } catch (UnixException e1) {
+                if (e1.errno() == EACCES) {
                     try {
-                        fchmod(fd, mode);
-                    } finally {
-                        close(fd);
+                        fd = open(file, O_WRONLY, O_NOFOLLOW);
+                    } catch (UnixException e2) {
+                        e2.rethrowAsIOException(file);
                     }
+                } else {
+                    e1.rethrowAsIOException(file);
                 }
-            } catch (UnixException x) {
-                x.rethrowAsIOException(file);
             }
+
+            try {
+                try {
+                    fchmod(fd, mode);
+                } finally {
+                    close(fd);
+                }
+            } catch (UnixException e) {
+                e.rethrowAsIOException(file);
+            }
+
         }
 
         // chown

-------------

PR Comment: https://git.openjdk.org/jdk/pull/15214#issuecomment-1678648583