[PATCH v2 3/3] Strict XenStore entry parsing

[Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>]

This rejects bogus xenstore node values that include e.g. leading spaces
or overflow the expected integer type.

Signed-off-by: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
---
 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