[PATCH v4 5/6] powerpc/eeh: fix potential OoB

[Markus Burri <markus.burri@mt.com>]

The buffer is set to 20 characters. If a caller write more characters,
count is truncated to the max available space in "simple_write_to_buffer".
To protect from OoB access, check that the input size fit into buffer and
add a zero terminator after copy to the end of the copied data.

Signed-off-by: Markus Burri <markus.burri@mt.com>
---
 arch/powerpc/kernel/eeh.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/eeh.c b/arch/powerpc/kernel/eeh.c
index 83fe99861eb1..92ef05d3678d 100644
--- a/arch/powerpc/kernel/eeh.c
+++ b/arch/powerpc/kernel/eeh.c
@@ -1734,10 +1734,15 @@ static ssize_t eeh_force_recover_write(struct file *filp,
 	char buf[20];
 	int ret;
 
-	ret = simple_write_to_buffer(buf, sizeof(buf), ppos, user_buf, count);
+	if (count >= sizeof(buf))
+		return -EINVAL;
+
+	ret = simple_write_to_buffer(buf, sizeof(buf) - 1, ppos, user_buf, count);
 	if (!ret)
 		return -EFAULT;
 
+	buf[ret] = '\0';
+
 	/*
 	 * When PE is NULL the event is a "special" event. Rather than
 	 * recovering a specific PE it forces the EEH core to scan for failed
-- 
2.39.5