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immutable: prevent clients from reading past the end of share data, which would allow them to learn the cancellation secret

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Declare explicitly that we prevent this problem in the server's version dict.
fixes #1528 (there are two patches that are each a sufficient fix to #1528 and this is one of them)
This commit is contained in:
Zooko O'Whielacronx 2011-09-12 15:24:58 -07:00
parent 5476f67dc1
commit 20e2910c61
2 changed files with 3 additions and 4 deletions
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6
src/allmydata/storage/immutable.py
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@ -83,11 +83,9 @@ class ShareFile:
def read_share_data(self, offset, length): def read_share_data(self, offset, length):
precondition(offset >= 0) precondition(offset >= 0)
# reads beyond the end of the data are truncated. Reads that start # reads beyond the end of the data are truncated. Reads that start
# beyond the end of the data return an empty string. I wonder why # beyond the end of the data return an empty string.
# Python doesn't do the following computation for me?
seekpos = self._data_offset+offset seekpos = self._data_offset+offset
fsize = os.path.getsize(self.home) actuallength = max(0, min(length, self._lease_offset-seekpos))
actuallength = max(0, min(length, fsize-seekpos))
if actuallength == 0: if actuallength == 0:
return "" return ""
f = open(self.home, 'rb') f = open(self.home, 'rb')

1
src/allmydata/storage/server.py
View File

@ -222,6 +222,7 @@ class StorageServer(service.MultiService, Referenceable):
{ "maximum-immutable-share-size": remaining_space, { "maximum-immutable-share-size": remaining_space,
"tolerates-immutable-read-overrun": True, "tolerates-immutable-read-overrun": True,
"delete-mutable-shares-with-zero-length-writev": True, "delete-mutable-shares-with-zero-length-writev": True,
"prevents-read-past-end-of-share-data": True,
}, },
"application-version": str(allmydata.__full_version__), "application-version": str(allmydata.__full_version__),
} }