linux-kernel - [PATCH] IB/qib: Validate ->show()/store() callbacks before calling them

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Date:   Thu,  7 Nov 2019 08:50:25 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Dennis Dalessandro <dennis.dalessandro@...el.com>,
        Mike Marciniszyn <mike.marciniszyn@...el.com>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] IB/qib: Validate ->show()/store() callbacks before calling them

The permissions of the read-only or write-only sysfs files can be
changed (as root) and the user can then try to read a write-only file or
write to a read-only file which will lead to kernel crash here.

Protect against that by always validating the show/store callbacks.

Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
 drivers/infiniband/hw/qib/qib_sysfs.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/infiniband/hw/qib/qib_sysfs.c b/drivers/infiniband/hw/qib/qib_sysfs.c
index 3926be78036e..568b21eb6ea1 100644
--- a/drivers/infiniband/hw/qib/qib_sysfs.c
+++ b/drivers/infiniband/hw/qib/qib_sysfs.c
@@ -301,6 +301,9 @@ static ssize_t qib_portattr_show(struct kobject *kobj,
 	struct qib_pportdata *ppd =
 		container_of(kobj, struct qib_pportdata, pport_kobj);
 
+	if (!pattr->show)
+		return -EIO;
+
 	return pattr->show(ppd, buf);
 }
 
@@ -312,6 +315,9 @@ static ssize_t qib_portattr_store(struct kobject *kobj,
 	struct qib_pportdata *ppd =
 		container_of(kobj, struct qib_pportdata, pport_kobj);
 
+	if (!pattr->store)
+		return -EIO;
+
 	return pattr->store(ppd, buf, len);
 }
 
-- 
2.21.0.rc0.269.g1a574e7a288b