From 2373ee006137349a2f13209477f785396ffd59a8 Mon Sep 17 00:00:00 2001
From: Etan Kissling <etan@status.im>
Date: Mon, 13 Dec 2021 19:46:25 +0100
Subject: [PATCH] harden `ecnist` byte export against uninitialized key (#671)

Currently, `ecnist`'s `toBytes` and `getBytes` methods operate only on
properly initialized keys. If an un-initialized key is given, an
`IndexError` may be raised if the key's `xlen` / `qlen` property is
larger than the maximum buffer size. This patch hardens those functions
to report a proper error in that case.
Note that the library functions called by `init` and `initRaw` already
reject data that does not have the expected length, so these new checks
should not be reachable in practice.
---
 libp2p/crypto/ecnist.nim |  6 ++++++
 tests/testecnist.nim     | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/libp2p/crypto/ecnist.nim b/libp2p/crypto/ecnist.nim
index f0cf258aa..9e920dbff 100644
--- a/libp2p/crypto/ecnist.nim
+++ b/libp2p/crypto/ecnist.nim
@@ -381,11 +381,15 @@ proc toBytes*(seckey: EcPrivateKey, data: var openarray[byte]): EcResult[int] =
       c0.write(Asn1Tag.Oid, Asn1OidSecp521r1)
     c0.finish()
     offset = pubkey.getOffset()
+    if offset < 0:
+      return err(EcKeyIncorrectError)
     length = pubkey.key.qlen
     c1.write(Asn1Tag.BitString,
              pubkey.buffer.toOpenArray(offset, offset + length - 1))
     c1.finish()
     offset = seckey.getOffset()
+    if offset < 0:
+      return err(EcKeyIncorrectError)
     length = seckey.key.xlen
     p.write(1'u64)
     p.write(Asn1Tag.OctetString,
@@ -426,6 +430,8 @@ proc toBytes*(pubkey: EcPublicKey, data: var openarray[byte]): EcResult[int] =
     c.finish()
     p.write(c)
     let offset = getOffset(pubkey)
+    if offset < 0:
+      return err(EcKeyIncorrectError)
     let length = pubkey.key.qlen
     p.write(Asn1Tag.BitString,
             pubkey.buffer.toOpenArray(offset, offset + length - 1))
diff --git a/tests/testecnist.nim b/tests/testecnist.nim
index 27dc5cce7..76999a4f3 100644
--- a/tests/testecnist.nim
+++ b/tests/testecnist.nim
@@ -315,6 +315,9 @@ suite "EC NIST-P256/384/521 test suite":
         rkey2 == key
         rkey3 == key
         rkey4 == key
+      rkey1.key.xlen = rkey1.buffer.len + 1
+      check:
+        rkey1.getBytes == EcResult[seq[byte]].err(EcKeyIncorrectError)
 
   test "[secp256r1] Public key serialize/deserialize test":
     for i in 0..<TestsCount:
@@ -333,6 +336,9 @@ suite "EC NIST-P256/384/521 test suite":
         rkey2 == pair.pubkey
         rkey3 == pair.pubkey
         rkey4 == pair.pubkey
+      rkey1.key.qlen = rkey1.buffer.len + 1
+      check:
+        rkey1.getBytes == EcResult[seq[byte]].err(EcKeyIncorrectError)
 
   test "[secp256r1] ECDHE test":
     for i in 0..<TestsCount:
@@ -422,6 +428,9 @@ suite "EC NIST-P256/384/521 test suite":
         rkey2 == key
         rkey3 == key
         rkey4 == key
+      rkey1.key.xlen = rkey1.buffer.len + 1
+      check:
+        rkey1.getBytes == EcResult[seq[byte]].err(EcKeyIncorrectError)
 
   test "[secp384r1] Public key serialize/deserialize test":
     for i in 0..<TestsCount:
@@ -440,6 +449,9 @@ suite "EC NIST-P256/384/521 test suite":
         rkey2 == pair.pubkey
         rkey3 == pair.pubkey
         rkey4 == pair.pubkey
+      rkey1.key.qlen = rkey1.buffer.len + 1
+      check:
+        rkey1.getBytes == EcResult[seq[byte]].err(EcKeyIncorrectError)
 
   test "[secp384r1] ECDHE test":
     for i in 0..<TestsCount:
@@ -529,6 +541,9 @@ suite "EC NIST-P256/384/521 test suite":
         rkey2 == key
         rkey3 == key
         rkey4 == key
+      rkey1.key.xlen = rkey1.buffer.len + 1
+      check:
+        rkey1.getBytes == EcResult[seq[byte]].err(EcKeyIncorrectError)
 
   test "[secp521r1] Public key serialize/deserialize test":
     for i in 0..<TestsCount:
@@ -547,6 +562,9 @@ suite "EC NIST-P256/384/521 test suite":
         rkey2 == pair.pubkey
         rkey3 == pair.pubkey
         rkey4 == pair.pubkey
+      rkey1.key.qlen = rkey1.buffer.len + 1
+      check:
+        rkey1.getBytes == EcResult[seq[byte]].err(EcKeyIncorrectError)
 
   test "[secp521r1] ECDHE test":
     for i in 0..<TestsCount: