linux-kernel - [RFC/PATCH 1/2] pstore: Protect unlink with read

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Date:   Wed, 19 Oct 2016 10:23:40 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stefan Hajnoczi <stefanha@...hat.com>
Subject: [RFC/PATCH 1/2] pstore: Protect unlink with read_mutex

When update_ms is set, pstore_get_records() will be called when there's
a new entry.  But unlink can be called at the same time and might
contend with the open-read-close loop.  Depending on the implementation
of platform driver, it may be safe or not.  But I think it'd be better
to protect those race in the first place.

Cc: Stefan Hajnoczi <stefanha@...hat.com>
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 fs/pstore/inode.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
index 1781dc50762e..75728dfae0a6 100644
--- a/fs/pstore/inode.c
+++ b/fs/pstore/inode.c
@@ -197,11 +197,14 @@ static int pstore_unlink(struct inode *dir, struct dentry *dentry)
 	if (err)
 		return err;
 
-	if (p->psi->erase)
+	if (p->psi->erase) {
+		mutex_lock(&p->psi->read_mutex);
 		p->psi->erase(p->type, p->id, p->count,
 			      d_inode(dentry)->i_ctime, p->psi);
-	else
+		mutex_unlock(&p->psi->read_mutex);
+	} else {
 		return -EPERM;
+	}
 
 	return simple_unlink(dir, dentry);
 }
-- 
2.9.3