streamclone: consider secret changesets (BC) (issue5589)

Previously, a repo containing secret changesets would be served via
stream clone, transferring those secret changesets. While secret
changesets aren't meant to imply strong security (if you really
want to keep them secret, others shouldn't have read access to the
repo), we should at least make an effort to protect secret changesets
when possible.

After this commit, we no longer serve stream clones for repos
containing secret changesets by default. This is backwards
incompatible behavior. In case anyone is relying on the behavior,
we provide a config option to opt into the old behavior.

Note that this defense is only beneficial for remote repos
accessed via the wire protocol: if a client has access to the
files backing a repo, they can get to the raw data and see secret
revisions.

mercurial/help/config.txt

@@ -1658,6 +1658,10 b' Controls generic server settings.'
     the write lock while determining what data to transfer.
     (default: True)
 
+``uncompressedallowsecret``
+    Whether to allow stream clones when the repository contains secret
+    changesets. (default: False)
+
 ``preferuncompressed``
     When set, clients will try to use the uncompressed streaming
     protocol. (default: False)

mercurial/streamclone.py

@@ -13,6 +13,7 b' from .i18n import _'
 from . import (
     branchmap,
     error,
+    phases,
     store,
     util,
 )
@@ -162,9 +163,18 b' def maybeperformlegacystreamclone(pullop'
 
         repo.invalidate()
 
-def allowservergeneration(ui):
+def allowservergeneration(repo):
     """Whether streaming clones are allowed from the server."""
-    return ui.configbool('server', 'uncompressed', True, untrusted=True)
+    if not repo.ui.configbool('server', 'uncompressed', True, untrusted=True):
+        return False
+
+    # The way stream clone works makes it impossible to hide secret changesets.
+    # So don't allow this by default.
+    secret = phases.hassecret(repo)
+    if secret:
+        return repo.ui.configbool('server', 'uncompressedallowsecret', False)
+
+    return True
 
 # This is it's own function so extensions can override it.
 def _walkstreamfiles(repo):

mercurial/wireproto.py

@@ -754,7 +754,7 b' def _capabilities(repo, proto):'
     """
     # copy to prevent modification of the global list
     caps = list(wireprotocaps)
-    if streamclone.allowservergeneration(repo.ui):
+    if streamclone.allowservergeneration(repo):
         if repo.ui.configbool('server', 'preferuncompressed', False):
             caps.append('stream-preferred')
         requiredformats = repo.requirements & repo.supportedformats
@@ -946,7 +946,7 b' def stream(repo, proto):'
     capability with a value representing the version and flags of the repo
     it is serving. Client checks to see if it understands the format.
     '''
-    if not streamclone.allowservergeneration(repo.ui):
+    if not streamclone.allowservergeneration(repo):
         return '1\n'
 
     def getstream(it):

tests/test-clone-uncompressed.t

@@ -49,6 +49,77 b' Clone with background file closing enabl'
   bundle2-input-bundle: 1 parts total
   checking for updated bookmarks
 
+Cannot stream clone when there are secret changesets
+
+  $ hg -R server phase --force --secret -r tip
+  $ hg clone --uncompressed -U http://localhost:$HGPORT secret-denied
+  warning: stream clone requested but server has them disabled
+  requesting all changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 1 changesets with 1 changes to 1 files
+
+  $ killdaemons.py
+
+Streaming of secrets can be overridden by server config
+
+  $ cd server
+  $ hg --config server.uncompressedallowsecret=true serve -p $HGPORT -d --pid-file=hg.pid
+  $ cat hg.pid > $DAEMON_PIDS
+  $ cd ..
+
+  $ hg clone --uncompressed -U http://localhost:$HGPORT secret-allowed
+  streaming all changes
+  1027 files to transfer, 96.3 KB of data
+  transferred 96.3 KB in * seconds (*/sec) (glob)
+  searching for changes
+  no changes found
+
+  $ killdaemons.py
+
+Verify interaction between preferuncompressed and secret presence
+
+  $ cd server
+  $ hg --config server.preferuncompressed=true serve -p $HGPORT -d --pid-file=hg.pid
+  $ cat hg.pid > $DAEMON_PIDS
+  $ cd ..
+
+  $ hg clone -U http://localhost:$HGPORT preferuncompressed-secret
+  requesting all changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 1 changesets with 1 changes to 1 files
+
+  $ killdaemons.py
+
+Clone not allowed when full bundles disabled and can't serve secrets
+
+  $ cd server
+  $ hg --config server.disablefullbundle=true serve -p $HGPORT -d --pid-file=hg.pid
+  $ cat hg.pid > $DAEMON_PIDS
+  $ cd ..
+
+  $ hg clone --uncompressed http://localhost:$HGPORT secret-full-disabled
+  warning: stream clone requested but server has them disabled
+  requesting all changes
+  remote: abort: server has pull-based clones disabled
+  abort: pull failed on remote
+  (remove --pull if specified or upgrade Mercurial)
+  [255]
+
+Local stream clone with secrets involved
+(This is just a test over behavior: if you have access to the repo's files,
+there is no security so it isn't important to prevent a clone here.)
+
+  $ hg clone -U --uncompressed server local-secret
+  warning: stream clone requested but server has them disabled
+  requesting all changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 1 changesets with 1 changes to 1 files
 
 Stream clone while repo is changing: