[PATCH v3 4/4] Reject NUL bytes in xenstore nodes

[Demi Marie Obenour <demi@invisiblethingslab.com>]

This rejects bogus xenstore node values that include interior NUL
bytes.  These would be truncated by functions that expect NUL-terminated
strings.

Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
---
 drivers/xen/xenbus/xenbus_xs.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c
index 12e02eb01f5991b31db451cc57037205359b347f..7cb2a22a7698ac40c81add23476594d9f27de8d0 100644
--- a/drivers/xen/xenbus/xenbus_xs.c
+++ b/drivers/xen/xenbus/xenbus_xs.c
@@ -569,16 +569,20 @@ int xenbus_scanf(struct xenbus_transaction t,
 		 const char *dir, const char *node, const char *fmt, ...)
 {
 	va_list ap;
-	int ret;
+	int ret = 0;
+	unsigned int len;
 	char *val;
 
-	val = xenbus_read(t, dir, node, NULL);
+	val = xenbus_read(t, dir, node, &len);
 	if (IS_ERR(val))
 		return PTR_ERR(val);
+	if (strlen(val) != len)
+		goto bad;
 
 	va_start(ap, fmt);
 	ret = vsscanf(val, fmt, ap);
 	va_end(ap);
+bad:
 	kfree(val);
 	/* Distinctive errno. */
 	if (ret == 0)
@@ -636,15 +640,18 @@ int xenbus_gather(struct xenbus_transaction t, const char *dir, ...)
 	while (ret == 0 && (name = va_arg(ap, char *)) != NULL) {
 		const char *fmt = va_arg(ap, char *);
 		void *result = va_arg(ap, void *);
+		unsigned len;
 		char *p;
 
-		p = xenbus_read(t, dir, name, NULL);
+		p = xenbus_read(t, dir, name, &len);
 		if (IS_ERR(p)) {
 			ret = PTR_ERR(p);
 			break;
 		}
-		if (fmt) {
-			if (sscanf(p, fmt, result) == 0)
+		if (strlen(p) != len)
+			ret = -EINVAL;
+		else if (fmt) {
+			if (sscanf(p, fmt, result) <= 0)
 				ret = -EINVAL;
 			kfree(p);
 		} else
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab