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From:   Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
To:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Mika Westerberg <mika.westerberg@linux.intel.com>,
        Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
Subject: [PATCH v2 2/3] nvmem: check for NULL reg_read and reg_write before
 dereferencing
Thread-Topic: [PATCH v2 2/3] nvmem: check for NULL reg_read and reg_write
 before dereferencing
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Date:   Mon, 2 Mar 2020 15:43:02 +0000
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Return -EPERM if reg_read is NULL in bin_attr_nvmem_read() or if
reg_write is NULL in bin_attr_nvmem_write().

This prevents NULL dereferences such as the one described in
03cd45d2e219 ("thunderbolt: Prevent crash if non-active NVMem file is
read")

Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
---
 drivers/nvmem/nvmem-sysfs.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/nvmem/nvmem-sysfs.c b/drivers/nvmem/nvmem-sysfs.c
index 00d3259ea..9312e1d6f 100644
--- a/drivers/nvmem/nvmem-sysfs.c
+++ b/drivers/nvmem/nvmem-sysfs.c
@@ -56,6 +56,9 @@ static ssize_t bin_attr_nvmem_read(struct file *filp, struct kobject *kobj,
 
 	count = round_down(count, nvmem->word_size);
 
+	if (!nvmem->reg_read)
+		return -EPERM;
+
 	rc = nvmem->reg_read(nvmem->priv, pos, buf, count);
 
 	if (rc)
@@ -90,6 +93,9 @@ static ssize_t bin_attr_nvmem_write(struct file *filp, struct kobject *kobj,
 
 	count = round_down(count, nvmem->word_size);
 
+	if (!nvmem->reg_write)
+		return -EPERM;
+
 	rc = nvmem->reg_write(nvmem->priv, pos, buf, count);
 
 	if (rc)
-- 
2.25.1