wireproto: check permissions when executing "batch" command (BC) (SEC)

For as long as the "batch" command has existed (introduced by
bd88561afb4b and first released as part of Mercurial 1.9), that command
(like most wire commands introduced after 2008) lacked an entry in
the hgweb permissions table. And since we don't verify permissions if
an entry is missing from the permissions table, this meant that
executing a command via "batch" would bypass all permissions
checks.

The security implications are significant: a Mercurial HTTP server
would allow writes via "batch" wire protocol commands as long as
the HTTP request were processed by Mercurial and the process running
the Mercurial HTTP server had write access to the repository. The
Mercurial defaults of servers being read-only and the various web.*
config options to define access control were bypassed.

In addition, "batch" could be used to exfiltrate data from servers
that were configured to not allow read access.

Both forms of permissions bypass could be mitigated to some extent
by using HTTP authentication. This would prevent HTTP requests from
hitting Mercurial's server logic. However, any authenticated request
would still be able to bypass permissions checks via "batch" commands.

The easiest exploit was to send "pushkey" commands via "batch" and
modify the state of bookmarks, phases, and obsolescence markers.
However, I suspect a well-crafted HTTP request could trick the server
into running the "unbundle" wire protocol command, effectively
performing a full `hg push` to create new changesets on the remote.

This commit plugs this gaping security hole by having the "batch"
command perform permissions checking on each sub-command that is
being batched. We do this by threading a permissions checking
callable all the way to the protocol handler. The threading is a
bit hacky from a code perspective. But it preserves API compatibility,
which is the proper thing to do on the stable branch.

One of the subtle things we do is assume that a command with an
undefined permission is a "push" command. This is the safest thing to
do from a security perspective: we don't want to take chances that
a command could perform a write even though the server is configured
to not allow writes.

As the test changes demonstrate, it is no longer possible to bypass
permissions via the "batch" wire protocol command.

.. bc::

   The "batch" wire protocol command now enforces permissions of
   each invoked sub-command. Wire protocol commands must define
   their operation type or the "batch" command will assume they
   can write data and will prevent their execution on HTTP servers
   unless the HTTP request method is POST, the server is configured
   to allow pushes, and the (possibly authenticated) HTTP user is
   authorized to perform a push.

mercurial/hgweb/hgweb_mod.py

@@ -360,8 +360,10 b' class hgweb(object):'
             try:
                 if query:
                     raise ErrorResponse(HTTP_NOT_FOUND)
+
+                req.checkperm = lambda op: self.check_perm(rctx, req, op)
                 if cmd in perms:
-                    self.check_perm(rctx, req, perms[cmd])
+                    req.checkperm(perms[cmd])
                 return protocol.call(rctx.repo, req, cmd)
             except ErrorResponse as inst:
                 # A client that sends unbundle without 100-continue will

mercurial/hgweb/protocol.py

@@ -52,6 +52,7 b' class webproto(wireproto.abstractserverp'
         self.response = ''
         self.ui = ui
         self.name = 'http'
+        self.checkperm = req.checkperm
 
     def getargs(self, args):
         knownargs = self._args()

mercurial/wireproto.py

@@ -689,6 +689,8 b" def wireprotocommand(name, args=''):"
         return func
     return register
 
+# TODO define a more appropriate permissions type to use for this.
+permissions['batch'] = 'pull'
 @wireprotocommand('batch', 'cmds *')
 def batch(repo, proto, cmds, others):
     repo = repo.filtered("served")
@@ -701,6 +703,17 b' def batch(repo, proto, cmds, others):'
                 n, v = a.split('=')
                 vals[unescapearg(n)] = unescapearg(v)
         func, spec = commands[op]
+
+        # If the protocol supports permissions checking, perform that
+        # checking on each batched command.
+        # TODO formalize permission checking as part of protocol interface.
+        if util.safehasattr(proto, 'checkperm'):
+            # Assume commands with no defined permissions are writes / for
+            # pushes. This is the safest from a security perspective because
+            # it doesn't allow commands with undefined semantics from
+            # bypassing permissions checks.
+            proto.checkperm(permissions.get(op, 'push'))
+
         if spec:
             keys = spec.split()
             data = {}

tests/test-http-permissions.t

@@ -83,13 +83,12 b' web.deny_read=* prevents access to wire '
   read not authorized
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=listkeys+namespace%3Dphases'
-  200 Script output follows
+  401 read not authorized
   
-  cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b	1
-  publishing	True (no-eol)
+  0
+  read not authorized
+  [1]
 
 TODO custom commands don't check permissions
 
@@ -143,13 +142,12 b' web.deny_read=* with REMOTE_USER set sti'
   read not authorized
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=listkeys+namespace%3Dphases'
-  200 Script output follows
+  401 read not authorized
   
-  cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b	1
-  publishing	True (no-eol)
+  0
+  read not authorized
+  [1]
 
 TODO custom commands don't check permissions
 
@@ -201,13 +199,12 b' web.deny_read=<user> denies access to un'
   read not authorized
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=listkeys+namespace%3Dphases'
-  200 Script output follows
+  401 read not authorized
   
-  cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b	1
-  publishing	True (no-eol)
+  0
+  read not authorized
+  [1]
 
 TODO custom commands don't check permissions
 
@@ -254,13 +251,12 b' web.deny_read=<user> denies access to us'
   read not authorized
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=listkeys+namespace%3Dphases'
-  200 Script output follows
+  401 read not authorized
   
-  cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b	1
-  publishing	True (no-eol)
+  0
+  read not authorized
+  [1]
 
 TODO custom commands don't check permissions
 
@@ -461,13 +457,12 b' web.allow_read=<user> does not allow una'
   read not authorized
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=listkeys+namespace%3Dphases'
-  200 Script output follows
+  401 read not authorized
   
-  cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b	1
-  publishing	True (no-eol)
+  0
+  read not authorized
+  [1]
 
 TODO custom commands don't check permissions
 
@@ -514,13 +509,12 b' web.allow_read=<user> does not allow use'
   read not authorized
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=listkeys+namespace%3Dphases'
-  200 Script output follows
+  401 read not authorized
   
-  cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b	1
-  publishing	True (no-eol)
+  0
+  read not authorized
+  [1]
 
 TODO custom commands don't check permissions
 
@@ -621,13 +615,12 b' web.deny_read takes precedence over web.'
   read not authorized
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=listkeys+namespace%3Dphases'
-  200 Script output follows
+  401 read not authorized
   
-  cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b	1
-  publishing	True (no-eol)
+  0
+  read not authorized
+  [1]
 
 TODO custom commands don't check permissions
 
@@ -686,13 +679,12 b' web.allow-pull=false denies read access '
   pull not authorized
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=listkeys+namespace%3Dphases'
-  200 Script output follows
+  401 pull not authorized
   
-  cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b	1
-  publishing	True (no-eol)
+  0
+  pull not authorized
+  [1]
 
 TODO custom commands don't check permissions
 
@@ -742,16 +734,18 b' Attempting a write command with HTTP GET'
   push requires POST request
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=pushkey+namespace%3Dbookmarks%2Ckey%3Dbm%2Cold%3D%2Cnew%3Dcb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b'
-  200 Script output follows
+  405 push requires POST request
   
-  1
+  0
+  push requires POST request
+  [1]
 
   $ hg bookmarks
-     bm                        0:cb9a9f314b8b
+  no bookmarks set
   $ hg bookmark -d bm
+  abort: bookmark 'bm' does not exist
+  [255]
 
 TODO custom commands don't check permissions
 
@@ -781,16 +775,18 b' Attempting a write command with an unkno'
   push requires POST request
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=pushkey+namespace%3Dbookmarks%2Ckey%3Dbm%2Cold%3D%2Cnew%3Dcb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b'
-  200 Script output follows
+  405 push requires POST request
   
-  1
+  0
+  push requires POST request
+  [1]
 
   $ hg bookmarks
-     bm                        0:cb9a9f314b8b
+  no bookmarks set
   $ hg bookmark -d bm
+  abort: bookmark 'bm' does not exist
+  [255]
 
 TODO custom commands don't check permissions
 
@@ -823,16 +819,15 b' Pushing on a plaintext channel is disabl'
   ssl required
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=pushkey+namespace%3Dbookmarks%2Ckey%3Dbm%2Cold%3D%2Cnew%3Dcb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b'
-  200 Script output follows
+  403 ssl required
   
-  1
+  0
+  ssl required
+  [1]
 
   $ hg bookmarks
-     bm                        0:cb9a9f314b8b
-  $ hg book -d bm
+  no bookmarks set
 
 TODO custom commands don't check permissions
 
@@ -887,16 +882,15 b' web.deny_push=* denies pushing to unauth'
   push not authorized
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=pushkey+namespace%3Dbookmarks%2Ckey%3Dbm%2Cold%3D%2Cnew%3Dcb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b'
-  200 Script output follows
+  401 push not authorized
   
-  1
+  0
+  push not authorized
+  [1]
 
   $ hg bookmarks
-     bm                        0:cb9a9f314b8b
-  $ hg book -d bm
+  no bookmarks set
 
 TODO custom commands don't check permissions
 
@@ -945,16 +939,15 b' web.deny_push=* denies pushing to authen'
   push not authorized
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=pushkey+namespace%3Dbookmarks%2Ckey%3Dbm%2Cold%3D%2Cnew%3Dcb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b'
-  200 Script output follows
+  401 push not authorized
   
-  1
+  0
+  push not authorized
+  [1]
 
   $ hg bookmarks
-     bm                        0:cb9a9f314b8b
-  $ hg book -d bm
+  no bookmarks set
 
 TODO custom commands don't check permissions
 
@@ -1009,16 +1002,15 b' web.deny_push=<user> denies pushing to u'
   push not authorized
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=pushkey+namespace%3Dbookmarks%2Ckey%3Dbm%2Cold%3D%2Cnew%3Dcb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b'
-  200 Script output follows
+  401 push not authorized
   
-  1
+  0
+  push not authorized
+  [1]
 
   $ hg bookmarks
-     bm                        0:cb9a9f314b8b
-  $ hg book -d bm
+  no bookmarks set
 
 TODO custom commands don't check permissions
 
@@ -1067,16 +1059,15 b' web.deny_push=<user> denies pushing to u'
   push not authorized
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=pushkey+namespace%3Dbookmarks%2Ckey%3Dbm%2Cold%3D%2Cnew%3Dcb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b'
-  200 Script output follows
+  401 push not authorized
   
-  1
+  0
+  push not authorized
+  [1]
 
   $ hg bookmarks
-     bm                        0:cb9a9f314b8b
-  $ hg book -d bm
+  no bookmarks set
 
 TODO custom commands don't check permissions
 
@@ -1241,16 +1232,15 b' web.allow-push=<user> denies push to use'
   push not authorized
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=pushkey+namespace%3Dbookmarks%2Ckey%3Dbm%2Cold%3D%2Cnew%3Dcb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b'
-  200 Script output follows
+  401 push not authorized
   
-  1
+  0
+  push not authorized
+  [1]
 
   $ hg bookmarks
-     bm                        0:cb9a9f314b8b
-  $ hg book -d bm
+  no bookmarks set
 
 TODO custom commands don't check permissions
 
@@ -1367,16 +1357,15 b' web.deny_push takes precedence over web.'
   push not authorized
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=pushkey+namespace%3Dbookmarks%2Ckey%3Dbm%2Cold%3D%2Cnew%3Dcb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b'
-  200 Script output follows
+  401 push not authorized
   
-  1
+  0
+  push not authorized
+  [1]
 
   $ hg bookmarks
-     bm                        0:cb9a9f314b8b
-  $ hg book -d bm
+  no bookmarks set
 
 TODO custom commands don't check permissions
 
@@ -1432,16 +1421,15 b' web.allow-push has no effect if web.deny'
   read not authorized
   [1]
 
-TODO batch command doesn't check permissions
-
   $ get-with-headers.py $LOCALIP:$HGPORT '?cmd=batch' --requestheader 'x-hgarg-1=cmds=pushkey+namespace%3Dbookmarks%2Ckey%3Dbm%2Cold%3D%2Cnew%3Dcb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b'
-  200 Script output follows
+  401 read not authorized
   
-  1
+  0
+  read not authorized
+  [1]
 
   $ hg bookmarks
-     bm                        0:cb9a9f314b8b
-  $ hg book -d bm
+  no bookmarks set
 
 TODO custom commands don't check permissions