From: Brian Warner <warner@allmydata.com>
Date: Thu, 8 Nov 2007 21:02:36 +0000 (-0700)
Subject: mutable: verify incoming share signatures during Publish, it's not that expensive... 
X-Git-Tag: allmydata-tahoe-0.7.0~240
X-Git-Url: https://git.rkrishnan.org/somewhere?a=commitdiff_plain;h=30a91c84c8232bbb86de6b6406b90d45a5e2d4aa;p=tahoe-lafs%2Ftahoe-lafs.git

mutable: verify incoming share signatures during Publish, it's not that expensive and it's a good idea
---

diff --git a/src/allmydata/mutable.py b/src/allmydata/mutable.py
index 20b0429a..d7a0d669 100644
--- a/src/allmydata/mutable.py
+++ b/src/allmydata/mutable.py
@@ -745,11 +745,13 @@ class Publish:
             (seqnum, root_hash, IV, k, N, segsize, datalen,
              pubkey_s, signature, prefix) = r
 
-            # TODO: consider verifying the signature here. It's expensive.
-            # What can an attacker (in this case the server) accomplish? They
-            # could make us think that there's a newer version of the file
-            # out there, which would cause us to throw
-            # UncoordinatedWriteError (i.e. it's a DoS attack).
+            # self._pubkey is present because we require read-before-replace
+            valid = self._pubkey.verify(prefix, signature)
+            if not valid:
+                self.log("WEIRD: bad signature from %s shnum %d" %
+                         (shnum, idlib.shortnodeid_b2a(peerid)))
+                continue
+
             share = (shnum, seqnum, root_hash)
             current_share_peers.add(shnum, (peerid, seqnum, root_hash) )