GHSA-59hh-656j-3p7v

### Impact

A vulnerable node is susceptible to crash when processing a maliciously crafted message from a peer, via the `snap/1` protocol. The crash can be triggered by sending a malicious `snap/1` `GetTrieNodes` package.

### Details

On September 21, 2021, geth-team member Gary Rong (@rjl493456442) found a way to crash the snap request handler .
By using this vulnerability, a peer connected on the `snap/1` protocol could cause a vulnerable node to crash with a `panic`.

In the `trie.TryGetNode` implementation, if the requested path is reached, the associated node will be returned. However the nilness is
not checked there.

```golang
func (t *Trie) tryGetNode(origNode node, path []byte, pos int) (item []byte, newnode node, resolved int, err error) {
// If we reached the requested path, return the current node
if pos >= len(path) {
// Although we most probably have the original node expanded, encoding
// that into consensus form can be nasty (needs to cascade down) and
// time consuming. Instead, just pull the hash up from disk directly.
var hash hashNode
if node, ok := origNode.(hashNode); ok {
hash = node
} else {
hash, _ = origNode.cache()
}
```
More specifically the `origNode` can be nil(e.g. the child of fullnode) and system can panic at line `hash, _ = origNode.cache()`.

When investigating this, @holiman tried to find it via fuzzing, which uncovered a second crasher, also related to the snap `GetTrieNodes` package. If the caller requests a storage trie:
```golang
// Storage slots requested, open the storage trie and retrieve from there
account, err := snap.Account(common.BytesToHash(pathset[0]))
loads++ // always account database reads, even for failures
if account == nil {
break
}
stTrie, err := trie.NewSecure(common.BytesToHash(account.Root), triedb)
```
The code assumes that `snap.Account` returns _either_ a non-nil response unless `error` is also provided. This is however not the case, since `snap.Account` can return `nil, nil`.

### Patches

```diff
--- a/eth/protocols/snap/handler.go
+++ b/eth/protocols/snap/handler.go
@@ -469,7 +469,7 @@ func handleMessage(backend Backend, peer *Peer) error {
// Storage slots requested, open the storage trie and retrieve from there
account, err := snap.Account(common.BytesToHash(pathset[0]))
loads++ // always account database reads, even for failures
- if err != nil {
+ if err != nil || account == nil {
break
}
stTrie, err := trie.NewSecure(common.BytesToHash(account.Root), triedb)
diff --git a/trie/trie.go b/trie/trie.go
index 7ea7efa835..d0f0d4e2bc 100644
--- a/trie/trie.go
+++ b/trie/trie.go
@@ -174,6 +174,10 @@ func (t *Trie) TryGetNode(path []byte) ([]byte, int, error) {
}

func (t *Trie) tryGetNode(origNode node, path []byte, pos int) (item []byte, newnode node, resolved int, err error) {
+ // If non-existent path requested, abort
+ if origNode == nil {
+ return nil, nil, 0, nil
+ }
// If we reached the requested path, return the current node
if pos >= len(path) {
// Although we most probably have the original node expanded, encoding
@@ -193,10 +197,6 @@ func (t *Trie) tryGetNode(origNode node, path []byte, pos int) (item []byte, new
}
// Path still needs to be traversed, descend into children
switch n := (origNode).(type) {
- case nil:
- // Non-existent path requested, abort
- return nil, nil, 0, nil
-
case valueNode:
// Path prematurely ended, abort
return nil, nil, 0, nil

```
The fixes were merged into [#23657](https://github.com/ethereum/go-ethereum/pull/23657), with commit [f1fd963](https://github.com/ethereum/go-ethereum/pull/23657/commits/f1fd963a5a965e643e52fcf805a2a02a323c32b8), and released as part of Geth [v1.10.9](https://github.com/ethereum/go-ethereum/tree/v1.10.9) on Sept 29, 2021.

### Workarounds

Apply the patch above or upgrade to a version which is not vulnerable.

### For more information
If you have any questions or comments about this advisory:
* Open an issue in [go-ethereum](https://github.com/ethereum/go-ethereum/)
* Email us at [[email protected]](mailto:[email protected])