[PATCH 06/10] pstore: Add proper unregister lock checking

From: Kees Cook
Date: Wed May 06 2020 - 11:22:15 EST


The pstore backend lock wasn't being used during pstore_unregister().
Add sanity check and locking.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
fs/pstore/platform.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index d0ce22237589..03bc847a6951 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -69,8 +69,9 @@ static void pstore_dowork(struct work_struct *);
static DECLARE_WORK(pstore_work, pstore_dowork);

/*
- * psinfo_lock just protects "psinfo" during
- * calls to pstore_register()
+ * psinfo_lock protects "psinfo" during calls to
+ * pstore_register(), pstore_unregister(), and
+ * the filesystem mount/unmount routines.
*/
static DEFINE_MUTEX(psinfo_lock);
struct pstore_info *psinfo;
@@ -626,6 +627,18 @@ EXPORT_SYMBOL_GPL(pstore_register);

void pstore_unregister(struct pstore_info *psi)
{
+ /* It's okay to unregister nothing. */
+ if (!psi)
+ return;
+
+ mutex_lock(&psinfo_lock);
+
+ /* Only one backend can be registered at a time. */
+ if (WARN_ON(psi != psinfo)) {
+ mutex_unlock(&psinfo_lock);
+ return;
+ }
+
/* Stop timer and make sure all work has finished. */
pstore_update_ms = -1;
del_timer_sync(&pstore_timer);
@@ -644,6 +657,7 @@ void pstore_unregister(struct pstore_info *psi)

psinfo = NULL;
backend = NULL;
+ mutex_unlock(&psinfo_lock);
}
EXPORT_SYMBOL_GPL(pstore_unregister);

--
2.20.1