[PATCH v2] hfsplus: preserve FinderInfo when listing extended attributes

[Hengyu Liang <hengyul@cs.unc.edu>]

Commit aef507847129 ("hfsplus: fix generic/062 xfstests failure") made
hfsplus_listxattr() return zero when the inode has no records in the
attributes B-tree.

However, osx.com.apple.FinderInfo is stored in the catalog record, and
hfsplus_listxattr() has already added it to the result at that point.
Setting the result to zero drops it. As of now, a file whose only
extended attribute is FinderInfo gets an empty list on a volume with
an attributes B-tree, which mkfs.hfsplus creates by default. getxattr()
still returns the value.

The issue can be reproduced with:

    truncate -s 64M hfs.img
    mkfs.hfsplus hfs.img
    mount -o loop hfs.img /mnt
    touch /mnt/file
    v=0x54455854$(printf %056d 0)
    setfattr -n osx.com.apple.FinderInfo -v $v /mnt/file
    getfattr -m - /mnt/file

Without this patch, getfattr prints nothing. With this patch, it lists
the FinderInfo entry.

This patch keeps the result of hfsplus_listxattr_finder_info() when no
attributes B-tree records are found, as is already done when the
volume has no attributes B-tree. A file without extended attributes
still gets an empty list.

Fixes: aef507847129 ("hfsplus: fix generic/062 xfstests failure")
Cc: stable@vger.kernel.org
Signed-off-by: Hengyu Liang <hengyul@cs.unc.edu>
---
Changes in v2:
- Restructure the error check as suggested by Viacheslav Dubeyko. No
  functional change.
- v1: https://lore.kernel.org/r/20261021174534.482192-1-hengyul@cs.unc.edu

Tested in KVM with KASAN on a804c5742bff, without and with this patch:
- The commands above, and a C test of listxattr() sizes and buffer
  lengths: a file with only FinderInfo gives 0 without the patch and
  25 with it; a file without extended attributes gives 0 on both.
- generic/062: 10/10 passed on both kernels.
- Full fstests (805 generic tests, 608 not run on both kernels): 186
  passed and 11 failed without the patch, 187 and 10 with it. The only
  difference is generic/795, which fails at random on both kernels
  with fsck "Invalid volume file count" (1 of 11 runs without the
  patch, 2 of 11 with it). generic/089 and a small test that only
  creates files and unlinks them while open hit the same error on both
  kernels. This looks like a separate race: hfsplus_file_release()
  updates file_count without vh_mutex.

With this patch, getfattr above prints "osx.com.apple.FinderInf". The
last character is lost by a separate bug in copy_name(), which Maurycy
Pawlowski-Wieronski's patch fixes:
https://lore.kernel.org/all/20260828-hfsplus-copy_name-fix-v1-1-75ed9f0f378c@maurycy.com/

 fs/hfsplus/xattr.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/fs/hfsplus/xattr.c b/fs/hfsplus/xattr.c
index 71364e093fa7..45571d6f3abd 100644
--- a/fs/hfsplus/xattr.c
+++ b/fs/hfsplus/xattr.c
@@ -837,13 +837,9 @@ ssize_t hfsplus_listxattr(struct dentry *dentry, char *buffer, size_t size)
 
 	err = hfsplus_find_attr(inode->i_sb, inode->i_ino, NULL, &fd);
 	if (err) {
-		if (err == -ENOENT || err == -ENODATA) {
-			res = 0;
-			goto end_listxattr;
-		} else {
+		if (err != -ENOENT && err != -ENODATA)
 			res = err;
-			goto end_listxattr;
-		}
+		goto end_listxattr;
 	}
 
 	for (;;) {

base-commit: a804c5742bff224d4cb4d25dd383554d598be32b
-- 
2.53.0