[PATCH v2 1/4] ext4: register 'orphan_list' procfs

[Ye Bin <yebin@huaweicloud.com>]

From: Ye Bin <yebin10@huawei.com>

This patch register '/proc/fs/ext4/XXX/orphan_list' procfs for show inode
orphan list about EXT4 file system.
In actual production environments, there may be inconsistencies in df/du,
sometimes due to kernel occupation, making it difficult to find such files,
and it is also difficult to operate in the current network environment. So
add "orphan_list" procfs to quickly query files that have been deleted but
are occupied.

Signed-off-by: Ye Bin <yebin10@huawei.com>
---
 fs/ext4/ext4.h   |  1 +
 fs/ext4/orphan.c | 77 ++++++++++++++++++++++++++++++++++++++++++++++++
 fs/ext4/sysfs.c  |  2 ++
 3 files changed, 80 insertions(+)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 0cf68f85dfd1..ccb0fd1e63e7 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -3875,6 +3875,7 @@ extern void ext4_stop_mmpd(struct ext4_sb_info *sbi);
 extern const struct fsverity_operations ext4_verityops;
 
 /* orphan.c */
+extern const struct proc_ops ext4_orphan_proc_ops;
 extern int ext4_orphan_add(handle_t *, struct inode *);
 extern int ext4_orphan_del(handle_t *, struct inode *);
 extern void ext4_orphan_cleanup(struct super_block *sb,
diff --git a/fs/ext4/orphan.c b/fs/ext4/orphan.c
index 64ea47624233..f7e7f77e021e 100644
--- a/fs/ext4/orphan.c
+++ b/fs/ext4/orphan.c
@@ -4,6 +4,8 @@
 #include <linux/fs.h>
 #include <linux/quotaops.h>
 #include <linux/buffer_head.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
 
 #include "ext4.h"
 #include "ext4_jbd2.h"
@@ -657,3 +659,78 @@ int ext4_orphan_file_empty(struct super_block *sb)
 			return 0;
 	return 1;
 }
+
+struct ext4_proc_orphan {
+	struct ext4_inode_info cursor;
+};
+
+static void *ext4_orphan_seq_start(struct seq_file *seq, loff_t *pos)
+{
+	return NULL;
+}
+
+static void *ext4_orphan_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+{
+	return NULL;
+}
+
+static int ext4_orphan_seq_show(struct seq_file *seq, void *v)
+{
+	return 0;
+}
+
+static void ext4_orphan_seq_stop(struct seq_file *seq, void *v)
+{
+}
+
+const struct seq_operations ext4_orphan_seq_ops = {
+	.start  = ext4_orphan_seq_start,
+	.next   = ext4_orphan_seq_next,
+	.stop   = ext4_orphan_seq_stop,
+	.show   = ext4_orphan_seq_show,
+};
+
+static int ext4_seq_orphan_open(struct inode *inode, struct file *file)
+{
+	int rc;
+	struct seq_file *m;
+	struct ext4_proc_orphan *private;
+
+	rc = seq_open_private(file, &ext4_orphan_seq_ops,
+			      sizeof(struct ext4_proc_orphan));
+	if (!rc) {
+		m = file->private_data;
+		private = m->private;
+		INIT_LIST_HEAD(&private->cursor.i_orphan);
+		private->cursor.vfs_inode.i_ino = 0;
+	}
+
+	return rc;
+}
+
+static int ext4_seq_orphan_release(struct inode *inode, struct file *file)
+{
+	struct seq_file *seq = file->private_data;
+	struct ext4_proc_orphan *s = seq->private;
+	struct ext4_sb_info *sbi = EXT4_SB(pde_data(inode));
+
+	/*
+	 * The function close_pdeo() is called when deleting the procfs
+	 * in ext4_unregister_sysfs(), and this function is used to remove
+	 * the entry from the 'pde->pde_openers' list. Therefore, when the
+	 * file is closed, proc_reg_release() will not call close_pdeo()
+	 * again because it cannot find the node on the 'pde->pde_openers'
+	 * list. This prevents the UAF issue from occurring.
+	 */
+	mutex_lock(&sbi->s_orphan_lock);
+	list_del(&s->cursor.i_orphan);
+	mutex_unlock(&sbi->s_orphan_lock);
+
+	return seq_release_private(inode, file);
+}
+
+const struct proc_ops ext4_orphan_proc_ops = {
+	.proc_open      = ext4_seq_orphan_open,
+	.proc_read      = seq_read,
+	.proc_release   = ext4_seq_orphan_release,
+};
diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
index 923b375e017f..b40a934e30c9 100644
--- a/fs/ext4/sysfs.c
+++ b/fs/ext4/sysfs.c
@@ -639,6 +639,8 @@ int ext4_register_sysfs(struct super_block *sb)
 				ext4_seq_mb_stats_show, sb);
 		proc_create_seq_data("mb_structs_summary", 0444, sbi->s_proc,
 				&ext4_mb_seq_structs_summary_ops, sb);
+		proc_create_data("orphan_list", 0400, sbi->s_proc,
+				 &ext4_orphan_proc_ops, sb);
 	}
 	return 0;
 }
-- 
2.34.1