blob: add a magic offset to nesting cookies to ensure that NULL is never returned...

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

diff --git a/blob.c b/blob.c
index 6d66fcd..faa3bb8 100644 (file)
--- a/blob.c
+++ b/blob.c
@@ -40,14 +40,14 @@ blob_init(struct blob_attr *attr, int id, unsigned int len)
 static inline struct blob_attr *
 offset_to_attr(struct blob_buf *buf, int offset)
 {
-       void *ptr = (char *)buf->buf + offset;
+       void *ptr = (char *)buf->buf + offset - BLOB_COOKIE;
        return ptr;
 }
 
 static inline int
 attr_to_offset(struct blob_buf *buf, struct blob_attr *attr)
 {
-       return (char *)attr - (char *) buf->buf;
+       return (char *)attr - (char *) buf->buf + BLOB_COOKIE;
 }
 
 void
@@ -65,7 +65,7 @@ static struct blob_attr *
 blob_add(struct blob_buf *buf, struct blob_attr *pos, int id, int payload)
 {
        int offset = attr_to_offset(buf, pos);
-       int required = (offset + sizeof(struct blob_attr) + payload) - buf->buflen;
+       int required = (offset - BLOB_COOKIE + sizeof(struct blob_attr) + payload) - buf->buflen;
        struct blob_attr *attr;
 
        if (required > 0) {

diff --git a/blob.h b/blob.h
index 846de6e..fa430a8 100644 (file)
--- a/blob.h
+++ b/blob.h
@@ -28,6 +28,8 @@
 
 #include "utils.h"
 
+#define BLOB_COOKIE            0x01234567
+
 enum {
        BLOB_ATTR_UNSPEC,
        BLOB_ATTR_NESTED,

diff --git a/blobmsg.c b/blobmsg.c
index 62f83cc..3076620 100644 (file)
--- a/blobmsg.c
+++ b/blobmsg.c
@@ -195,7 +195,7 @@ blobmsg_new(struct blob_buf *buf, int type, const char *name, int payload_len, v
 static inline int
 attr_to_offset(struct blob_buf *buf, struct blob_attr *attr)
 {
-       return (char *)attr - (char *) buf->buf;
+       return (char *)attr - (char *) buf->buf + BLOB_COOKIE;
 }
 
 
@@ -262,7 +262,7 @@ void *
 blobmsg_realloc_string_buffer(struct blob_buf *buf, int maxlen)
 {
        struct blob_attr *attr = blob_next(buf->head);
-       int offset = attr_to_offset(buf, blob_next(buf->head)) + blob_pad_len(attr);
+       int offset = attr_to_offset(buf, blob_next(buf->head)) + blob_pad_len(attr) - BLOB_COOKIE;
        int required = maxlen - (buf->buflen - offset);
 
        if (required <= 0)