[PATCH next] ACPI: APEI: EINJ: prevent memory corruption in error_type_set()

[Dan Carpenter <dan.carpenter@linaro.org>]

The "einj_buf" buffer is 32 chars.  Verify that "count" is not too large
for that.  Also leave the last character as a NUL terminator to ensure
the string is properly terminated.

Fixes: 0c6176e1e186 ("ACPI: APEI: EINJ: Enable the discovery of EINJv2 capabilities")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
---
 drivers/acpi/apei/einj-core.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/apei/einj-core.c b/drivers/acpi/apei/einj-core.c
index d6d7e36e3647..e77c0d4b4ee5 100644
--- a/drivers/acpi/apei/einj-core.c
+++ b/drivers/acpi/apei/einj-core.c
@@ -826,8 +826,11 @@ static ssize_t error_type_set(struct file *file, const char __user *buf,
 	int rc;
 	u64 val;
 
+	if (count > sizeof(einj_buf))
+		return -EINVAL;
+
 	memset(einj_buf, 0, sizeof(einj_buf));
-	if (copy_from_user(einj_buf, buf, count))
+	if (copy_from_user(einj_buf, buf, min(count, sizeof((einj_buf) - 1))))
 		return -EFAULT;
 
 	if (strncmp(einj_buf, "V2_", 3) == 0) {
-- 
2.47.2