[PATCH] selinux: replace strlcat() with seq_buf in selinux_ima_collect_state()

[Ian Bridges <icb@fastmail.org>]

In preparation for removing the deprecated strlcat() API[1], replace the
strscpy()/strlcat() chain in selinux_ima_collect_state() with a struct
seq_buf, which tracks the write position and remaining space internally.

The seven open-coded WARN_ON(rc >= buf_len) truncation checks become a
single seq_buf_has_overflowed() check after the string is built. The
kzalloc() and its exact-size computation are unchanged, so the
measurement string passed to IMA is unchanged.

Link: https://github.com/KSPP/linux/issues/370 [1]
Signed-off-by: Ian Bridges <icb@fastmail.org>
---
 security/selinux/ima.c | 35 ++++++++++++++---------------------
 1 file changed, 14 insertions(+), 21 deletions(-)

diff --git a/security/selinux/ima.c b/security/selinux/ima.c
index aa34da9b0aeb..3d81093d16aa 100644
--- a/security/selinux/ima.c
+++ b/security/selinux/ima.c
@@ -9,6 +9,7 @@
  */
 #include <linux/vmalloc.h>
 #include <linux/ima.h>
+#include <linux/seq_buf.h>
 #include "security.h"
 #include "ima.h"
 
@@ -21,8 +22,9 @@
 static char *selinux_ima_collect_state(void)
 {
 	const char *on = "=1;", *off = "=0;";
+	struct seq_buf s;
 	char *buf;
-	int buf_len, len, i, rc;
+	int buf_len, len, i;
 
 	buf_len = strlen("initialized=0;enforcing=0;checkreqprot=0;") + 1;
 
@@ -34,33 +36,24 @@ static char *selinux_ima_collect_state(void)
 	if (!buf)
 		return NULL;
 
-	rc = strscpy(buf, "initialized", buf_len);
-	WARN_ON(rc < 0);
+	seq_buf_init(&s, buf, buf_len);
 
-	rc = strlcat(buf, selinux_initialized() ? on : off, buf_len);
-	WARN_ON(rc >= buf_len);
+	seq_buf_puts(&s, "initialized");
+	seq_buf_puts(&s, selinux_initialized() ? on : off);
 
-	rc = strlcat(buf, "enforcing", buf_len);
-	WARN_ON(rc >= buf_len);
+	seq_buf_puts(&s, "enforcing");
+	seq_buf_puts(&s, enforcing_enabled() ? on : off);
 
-	rc = strlcat(buf, enforcing_enabled() ? on : off, buf_len);
-	WARN_ON(rc >= buf_len);
-
-	rc = strlcat(buf, "checkreqprot", buf_len);
-	WARN_ON(rc >= buf_len);
-
-	rc = strlcat(buf, checkreqprot_get() ? on : off, buf_len);
-	WARN_ON(rc >= buf_len);
+	seq_buf_puts(&s, "checkreqprot");
+	seq_buf_puts(&s, checkreqprot_get() ? on : off);
 
 	for (i = 0; i < __POLICYDB_CAP_MAX; i++) {
-		rc = strlcat(buf, selinux_policycap_names[i], buf_len);
-		WARN_ON(rc >= buf_len);
-
-		rc = strlcat(buf, selinux_state.policycap[i] ? on : off,
-			buf_len);
-		WARN_ON(rc >= buf_len);
+		seq_buf_puts(&s, selinux_policycap_names[i]);
+		seq_buf_puts(&s, selinux_state.policycap[i] ? on : off);
 	}
 
+	WARN_ON(seq_buf_has_overflowed(&s));
+
 	return buf;
 }
 
-- 
2.47.3