[PATCH v3 7/8] userns: Replace strncmp with str_has_prefix

[Chuhong Yuan]

strncmp(str, const, len) is error-prone because len
is easy to have typo.
The example is the hard-coded len has counting error
or sizeof(const) forgets - 1.
So we prefer using newly introduced str_has_prefix()
to substitute such strncmp to make code better.

Signed-off-by: Chuhong Yuan <hslester96@xxxxxxxxx>
---
Changes in v3:
  - Revise the description.

 kernel/user_namespace.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 8eadadc478f9..e231e902df8a 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -1138,6 +1138,7 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
 	char kbuf[8], *pos;
 	bool setgroups_allowed;
 	ssize_t ret;
+	size_t len;
 
 	/* Only allow a very narrow range of strings to be written */
 	ret = -EINVAL;
@@ -1153,12 +1154,11 @@ ssize_t proc_setgroups_write(struct file *file, const char __user *buf,
 
 	/* What is being requested? */
 	ret = -EINVAL;
-	if (strncmp(pos, "allow", 5) == 0) {
-		pos += 5;
+	if ((len = str_has_prefix(pos, "allow"))) {
+		pos += len;
 		setgroups_allowed = true;
-	}
-	else if (strncmp(pos, "deny", 4) == 0) {
-		pos += 4;
+	} else if ((len = str_has_prefix(pos, "deny"))) {
+		pos += len;
 		setgroups_allowed = false;
 	}
 	else
-- 
2.20.1