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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Xiao Ni <xni@redhat.com>,
        NeilBrown <neilb@suse.com>, Yufen Yu <yuyufen@huawei.com>,
        Song Liu <songliubraving@fb.com>
Subject: [PATCH 4.4 038/241] md: add mddev->pers to avoid potential NULL pointer dereference
Date:   Sun,  9 Jun 2019 18:39:40 +0200
Message-Id: <20190609164148.872968428@linuxfoundation.org>
In-Reply-To: <20190609164147.729157653@linuxfoundation.org>
References: <20190609164147.729157653@linuxfoundation.org>
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From: Yufen Yu <yuyufen@huawei.com>

commit ee37e62191a59d253fc916b9fc763deb777211e2 upstream.

When doing re-add, we need to ensure rdev->mddev->pers is not NULL,
which can avoid potential NULL pointer derefence in fallowing
add_bound_rdev().

Fixes: a6da4ef85cef ("md: re-add a failed disk")
Cc: Xiao Ni <xni@redhat.com>
Cc: NeilBrown <neilb@suse.com>
Cc: <stable@vger.kernel.org> # 4.4+
Reviewed-by: NeilBrown <neilb@suse.com>
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/md/md.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -2690,8 +2690,10 @@ state_store(struct md_rdev *rdev, const
 			err = 0;
 		}
 	} else if (cmd_match(buf, "re-add")) {
-		if (test_bit(Faulty, &rdev->flags) && (rdev->raid_disk == -1) &&
-			rdev->saved_raid_disk >= 0) {
+		if (!rdev->mddev->pers)
+			err = -EINVAL;
+		else if (test_bit(Faulty, &rdev->flags) && (rdev->raid_disk == -1) &&
+				rdev->saved_raid_disk >= 0) {
 			/* clear_bit is performed _after_ all the devices
 			 * have their local Faulty bit cleared. If any writes
 			 * happen in the meantime in the local node, they