* Add LeaseSetBufferValidate which checks lease validity and extracts timestamp

* check for leases with LeaseSetBufferValidate before update in floodfill code as to prevent malicous nodes removing good LS

libi2pd/LeaseSet.cpp

@@ -265,5 +265,39 @@ namespace data
 		auto ts = i2p::util::GetMillisecondsSinceEpoch ();
 		return ts > m_ExpirationTime;
 	}
+
+	bool LeaseSetBufferValidate(const uint8_t * ptr, size_t sz, uint64_t & expires)
+	{
+		IdentityEx ident(ptr, sz);
+		size_t size = ident.GetFullLen ();
+		if (size > sz)
+		{
+			LogPrint (eLogError, "LeaseSet: identity length ", size, " exceeds buffer size ", sz);
+			return false;
+		}
+		// encryption key
+		size += 256;
+		// signing key (unused)
+		size += ident.GetSigningPublicKeyLen ();
+		uint8_t numLeases = ptr[size];
+		++size;
+		if (!numLeases || numLeases > MAX_NUM_LEASES)
+		{
+			LogPrint (eLogError, "LeaseSet: incorrect number of leases", (int)numLeases);
+			return false;
+		}
+		const uint8_t * leases = ptr + size;
+		expires = 0;
+		/** find lease with the max expiration timestamp */
+		for (int i = 0; i < numLeases; i++)
+		{
+			leases += 36; // gateway + tunnel ID
+			uint64_t endDate = bufbe64toh (leases);
+			leases += 8; // end date
+			if(endDate > expires)
+				expires = endDate;
+		}
+		return ident.Verify(ptr, leases - ptr, leases);
+	}
 }
 }

libi2pd/LeaseSet.h

@@ -95,6 +95,12 @@ namespace data
 			size_t m_BufferLen;
 	};
 
+	/**
+			validate lease set buffer signature and extract expiration timestamp
+			@returns true if the leaseset is well formed and signature is valid
+	 */
+	bool LeaseSetBufferValidate(const uint8_t * ptr, size_t sz, uint64_t & expires);
+
 	class LocalLeaseSet
 	{
 		public:

libi2pd/NetDb.cpp

@@ -237,22 +237,20 @@ namespace data
 			auto it = m_LeaseSets.find(ident);
 			if (it != m_LeaseSets.end ())
 			{
-				if (it->second->IsNewer (buf, len))
+				uint64_t expires;
+				if(LeaseSetBufferValidate(buf, len, expires))
 				{
-					it->second->Update (buf, len);
-					if (it->second->IsValid ())
+					if(it->second->GetExpirationTime() < expires)
 					{
+						it->second->Update (buf, len);
 						LogPrint (eLogInfo, "NetDb: LeaseSet updated: ", ident.ToBase32());
 						updated = true;
 					}
 					else
-					{
-						LogPrint (eLogWarning, "NetDb: LeaseSet update failed: ", ident.ToBase32());
-						m_LeaseSets.erase (it);
-					}
+						LogPrint(eLogDebug, "NetDb: LeaseSet is older: ", ident.ToBase32());
 				}
 				else
-					LogPrint (eLogDebug, "NetDb: LeaseSet is older: ", ident.ToBase32());
+					LogPrint(eLogError, "NetDb: LeaseSet is invalid: ", ident.ToBase32());
 			}
 			else
 			{