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Date:   Wed,  6 May 2020 08:21:14 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-kernel@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Luis Henriques <lhenriques@...e.com>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>
Subject: [PATCH 10/10] pstore: Remove filesystem records when backend is unregistered

If a backend was unloaded without having first removed all its
associated records in pstorefs, subsequent removals would crash while
attempting to call into the now missing backend. Add automatic removal
from the tree in pstore_unregister(), so that no references to the
backend remain.

Reported-by: Luis Henriques <lhenriques@...e.com>
Link: https://lore.kernel.org/lkml/87o8yrmv69.fsf@suse.com
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 fs/pstore/inode.c    | 30 ++++++++++++++++++++++++++++++
 fs/pstore/internal.h |  1 +
 fs/pstore/platform.c |  3 +++
 3 files changed, 34 insertions(+)

diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
index e13482c8e180..499d91a669bb 100644
--- a/fs/pstore/inode.c
+++ b/fs/pstore/inode.c
@@ -36,6 +36,7 @@ static struct super_block *pstore_sb;
 
 struct pstore_private {
 	struct list_head list;
+	struct dentry *dentry;
 	struct pstore_record *record;
 	size_t total_size;
 };
@@ -306,6 +307,34 @@ struct dentry *psinfo_lock_root(void)
 	return root;
 }
 
+int pstore_put_backend_records(struct pstore_info *psi)
+{
+	struct pstore_private *pos, *tmp;
+	struct dentry *root;
+	int rc = 0;
+
+	root = psinfo_lock_root();
+	if (!root)
+		return 0;
+
+	mutex_lock(&records_list_lock);
+	list_for_each_entry_safe(pos, tmp, &records_list, list) {
+		if (pos->record->psi == psi) {
+			list_del_init(&pos->list);
+			rc = simple_unlink(d_inode(root), pos->dentry);
+			if (WARN_ON(rc))
+				break;
+			d_delete(pos->dentry);
+			dput(pos->dentry);
+		}
+	}
+	mutex_unlock(&records_list_lock);
+
+	inode_unlock(d_inode(root));
+
+	return rc;
+}
+
 /*
  * Make a regular file in the root directory of our file system.
  * Load it up with "size" bytes of data from "buf".
@@ -352,6 +381,7 @@ int pstore_mkfile(struct dentry *root, struct pstore_record *record)
 	if (!dentry)
 		goto fail_private;
 
+	private->dentry = dentry;
 	private->record = record;
 	inode->i_size = private->total_size = size;
 	inode->i_private = private;
diff --git a/fs/pstore/internal.h b/fs/pstore/internal.h
index fe5f7ef7323f..8efd72d93b10 100644
--- a/fs/pstore/internal.h
+++ b/fs/pstore/internal.h
@@ -31,6 +31,7 @@ extern void	pstore_set_kmsg_bytes(int);
 extern void	pstore_get_records(int);
 extern void	pstore_get_backend_records(struct pstore_info *psi,
 					   struct dentry *root, int quiet);
+extern int	pstore_put_backend_records(struct pstore_info *psi);
 extern int	pstore_mkfile(struct dentry *root,
 			      struct pstore_record *record);
 extern void	pstore_record_init(struct pstore_record *record,
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index 03a17b401533..6fb526187953 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -658,6 +658,9 @@ void pstore_unregister(struct pstore_info *psi)
 	del_timer_sync(&pstore_timer);
 	flush_work(&pstore_work);
 
+	/* Remove all backend records from filesystem tree. */
+	pstore_put_backend_records(psi);
+
 	free_buf_for_compression();
 
 	psinfo = NULL;
-- 
2.20.1

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