blobmsg: fix attrs iteration in the blobmsg_check_array_len()

Starting with 75e300aeec25 ("blobmsg: fix wrong payload len passed from
blobmsg_check_array") blobmsg_check_array_len() gets *blob* length
passed as argument. It cannot be used with __blobmsg_for_each_attr()
which expects *data* length.

Use blobmsg_for_each_attr() which calculates *data* length on its own.

The same bug was already reported in the past and there was fix attempt
in the commit cd75136b1342 ("blobmsg: fix wrong payload len passed from
blobmsg_check_array"). That change made blobmsg_check_attr_len() calls
fail however.

This is hopefully the correct & complete fix:
1. blobmsg_check_array_len() gets *blob* length
2. It calls blobmsg_check_attr_len() which requires *blob* length
3. It uses blobmsg_for_each_attr() which gets *data* length

This fixes iterating over random memory treated as attrs. That was
resulting in check failing randomly for totally correct blobs. It's
critical e.g. for procd project with its instance_fill_array() failing
and procd not starting services.

Fixes: 75e300aeec25 ("blobmsg: fix wrong payload len passed from blobmsg_check_array")
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

diff --git a/blobmsg.c b/blobmsg.c
index 8b9877d7ce9e1cec5d0a37c0488244196d35575f..59045e1672c85efdf4431874230d45901aa7ad6e 100644 (file)
--- a/blobmsg.c
+++ b/blobmsg.c
@@ -117,16 +117,18 @@ int blobmsg_check_array(const struct blob_attr *attr, int type)
        return blobmsg_check_array_len(attr, type, blob_len(attr));
 }
 
-int blobmsg_check_array_len(const struct blob_attr *attr, int type, size_t len)
+int blobmsg_check_array_len(const struct blob_attr *attr, int type,
+                           size_t blob_len)
 {
        struct blob_attr *cur;
+       size_t rem;
        bool name;
        int size = 0;
 
        if (type > BLOBMSG_TYPE_LAST)
                return -1;
 
-       if (!blobmsg_check_attr_len(attr, false, len))
+       if (!blobmsg_check_attr_len(attr, false, blob_len))
                return -1;
 
        switch (blobmsg_type(attr)) {
@@ -140,11 +142,11 @@ int blobmsg_check_array_len(const struct blob_attr *attr, int type, size_t len)
                return -1;
        }
 
-       __blobmsg_for_each_attr(cur, attr, len) {
+       blobmsg_for_each_attr(cur, attr, rem) {
                if (type != BLOBMSG_TYPE_UNSPEC && blobmsg_type(cur) != type)
                        return -1;
 
-               if (!blobmsg_check_attr_len(cur, name, len))
+               if (!blobmsg_check_attr_len(cur, name, rem))
                        return -1;
 
                size++;