[PATCH] lockdown: avoid extra call to strlen() in lockdown_read()

[Dmitry Antipov]

Since s*printf() family of functions returns the number of characters
emitted, avoid redundant call to strlen() in lockdown_read() and prefer
snprintf() over sprintf() for an extra protection against buffer overflow.

Signed-off-by: Dmitry Antipov <dmantipov at yandex.ru>
---
 security/lockdown/lockdown.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index cf83afa1d879..10537d7c4437 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -106,9 +106,13 @@ static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count,
 			const char *label = lockdown_reasons[level];
 
 			if (kernel_locked_down == level)
-				offset += sprintf(temp+offset, "[%s] ", label);
+				offset += snprintf(temp + offset,
+						   sizeof(temp) - offset,
+						   "[%s] ", label);
 			else
-				offset += sprintf(temp+offset, "%s ", label);
+				offset += snprintf(temp + offset,
+						   sizeof(temp) - offset,
+						   "%s ", label);
 		}
 	}
 
@@ -116,7 +120,7 @@ static ssize_t lockdown_read(struct file *filp, char __user *buf, size_t count,
 	if (offset > 0)
 		temp[offset-1] = '\n';
 
-	return simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
+	return simple_read_from_buffer(buf, count, ppos, temp, offset);
 }
 
 static ssize_t lockdown_write(struct file *file, const char __user *buf,
-- 
2.50.1