[PATCH 1/2] hfs: do not end readdir at i_size after an unlink

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

Commit 7fde7e806657 ("hfs: rework hfsplus_readdir() logic") stopped
moving the position of open directories back when an entry is deleted.

However, hfs_readdir() still ends when ctx->pos reaches i_size, and
i_size drops on every delete. As of now, a program that reads a
directory and deletes what it read sees the directory end early and
leaves files behind.

The issue can be reproduced with BusyBox rm on a new hfs volume:

    mkdir /mnt/d
    (cd /mnt/d && for i in $(seq 1500); do : > f$i; done)
    rm -r /mnt/d

Before commit 7fde7e806657 ("hfs: rework hfsplus_readdir() logic"),
the directory is removed. After that commit, the result is:

    rm: can't remove '/mnt/d': Directory not empty

and 304 files are left.

This patch will end a walk that continues from the saved key where the
records of the directory end, and keep the i_size check for a walk that
starts from a position.

Fixes: 7fde7e806657 ("hfs: rework hfsplus_readdir() logic")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Hengyu Liang <hengyul@cs.unc.edu>
---
Application impact (Ubuntu 26.04 user space): a folder with 1500 files
on an HFS volume is moved to the trash, then the trash is emptied with
"gio trash --empty" (the call behind "Empty Trash" in GNOME Files, done
by gvfsd-trash 1.60). On v7.1, all files are removed. On v7.2, the trash
looks empty, but 478 files stay in .Trash-0/expunged and their space is
not freed.

 fs/hfs/dir.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/fs/hfs/dir.c b/fs/hfs/dir.c
index b6b8945712a9..b0858512f4d2 100644
--- a/fs/hfs/dir.c
+++ b/fs/hfs/dir.c
@@ -51,10 +51,16 @@ static int hfs_readdir(struct file *file, struct dir_context *ctx)
 	char strbuf[HFS_MAX_NAMELEN];
 	union hfs_cat_rec entry;
 	struct hfs_find_data fd;
-	struct hfs_readdir_data *rd;
+	struct hfs_readdir_data *rd = file->private_data;
+	/*
+	 * i_size follows the valence and drops on unlink, so it says nothing
+	 * about a walk that continues from a saved key. That walk ends where
+	 * the records of this directory end.
+	 */
+	bool resume = rd && rd->pos == ctx->pos;
 	u16 type;
 
-	if (ctx->pos >= inode->i_size)
+	if (!resume && ctx->pos >= inode->i_size)
 		return 0;
 
 	err = hfs_find_init(HFS_SB(sb)->cat_tree, &fd);
@@ -93,10 +99,9 @@ static int hfs_readdir(struct file *file, struct dir_context *ctx)
 			goto out;
 		ctx->pos = 2;
 	}
-	if (ctx->pos >= inode->i_size)
+	if (!resume && ctx->pos >= inode->i_size)
 		goto out;
-	rd = file->private_data;
-	if (rd && rd->pos == ctx->pos) {
+	if (resume) {
 		memcpy(fd.search_key, &rd->key, sizeof(struct hfs_cat_key));
 		err = hfs_brec_find(&fd);
 		if (err == -ENOENT)
@@ -105,10 +110,12 @@ static int hfs_readdir(struct file *file, struct dir_context *ctx)
 		err = hfs_brec_goto(&fd, ctx->pos - 1);
 	}
 	if (err)
-		goto out;
+		goto end_walk;
 
 	for (;;) {
 		if (be32_to_cpu(fd.key->cat.ParID) != inode->i_ino) {
+			if (resume)
+				goto out;
 			pr_err("walked past end of dir\n");
 			err = -EIO;
 			goto out;
@@ -146,11 +153,11 @@ static int hfs_readdir(struct file *file, struct dir_context *ctx)
 			goto out;
 		}
 		ctx->pos++;
-		if (ctx->pos >= inode->i_size)
+		if (!resume && ctx->pos >= inode->i_size)
 			goto out;
 		err = hfs_brec_goto(&fd, 1);
 		if (err)
-			goto out;
+			goto end_walk;
 	}
 	if (!rd) {
 		rd = kmalloc_obj(struct hfs_readdir_data);
@@ -162,6 +169,10 @@ static int hfs_readdir(struct file *file, struct dir_context *ctx)
 	}
 	rd->pos = ctx->pos;
 	memcpy(&rd->key, &fd.key->cat, sizeof(struct hfs_cat_key));
+end_walk:
+	/* This directory can hold the last records of the catalog. */
+	if (resume && err == -ENOENT)
+		err = 0;
 out:
 	hfs_find_exit(&fd);
 	return err;
-- 
2.53.0