From: Brian Warner <warner@allmydata.com>
Date: Wed, 13 Feb 2008 20:34:20 +0000 (-0700)
Subject: mutable.py: reject shares with different k/N than we expect. Quick fix for #312:... 
X-Git-Tag: allmydata-tahoe-0.8.0~71
X-Git-Url: https://git.rkrishnan.org/%3C?a=commitdiff_plain;h=8c8bcb6d531cfd3554b5fd807ff3808db455708b;p=tahoe-lafs%2Ftahoe-lafs.git

mutable.py: reject shares with different k/N than we expect. Quick fix for #312: avoids data corruption but has availability problems.
---

diff --git a/src/allmydata/mutable.py b/src/allmydata/mutable.py
index fc1b4c33..4459ee71 100644
--- a/src/allmydata/mutable.py
+++ b/src/allmydata/mutable.py
@@ -410,6 +410,9 @@ class Retrieve:
             self._valid_versions[verinfo] = (prefix, DictOfSets())
 
             # and make a note of the other parameters we've just learned
+            # NOTE: Retrieve needs to be refactored to put k,N in the verinfo
+            # along with seqnum/etc, to make sure we don't co-mingle shares
+            # from differently-encoded versions of the same file.
             if self._required_shares is None:
                 self._required_shares = k
                 self._node._populate_required_shares(k)
@@ -417,6 +420,23 @@ class Retrieve:
                 self._total_shares = N
                 self._node._populate_total_shares(N)
 
+        # reject shares that don't match our narrow-minded ideas of what
+        # encoding we're going to use. This addresses the immediate needs of
+        # ticket #312, by turning the data corruption into unavailability. To
+        # get back the availability (i.e. make sure that one weird-encoding
+        # share that happens to come back first doesn't make us ignore the
+        # rest of the shares), we need to implement the refactoring mentioned
+        # above.
+        if k != self._required_shares:
+            raise CorruptShareError(peerid, shnum,
+                                    "share has k=%d, we want k=%d" %
+                                    (k, self._required_shares))
+
+        if N != self._total_shares:
+            raise CorruptShareError(peerid, shnum,
+                                    "share has N=%d, we want N=%d" %
+                                    (N, self._total_shares))
+
         # we've already seen this pair, and checked the signature so we
         # know it's a valid candidate. Accumulate the share info, if
         # there's enough data present. If not, raise NeedMoreDataError,