hgweb: raw file mimetype guessing configurable, off by default (BC) (issue2923)

Before: hgweb made it possible to download file content with a content type
detected from the file extension. It would serve .html files as text/html and
could thus cause XSS vulnerabilities if the web site had any kind of session
authorization and the repository content wasn't fully trusted.

Now: all files default to "application/binary", which all important
browsers will refuse to treat as text/html. See the table here:

https://code.google.com/p/browsersec/wiki/Part2#Survey_of_content_sniffing_behaviors

mercurial/help/config.txt

@@ -1154,6 +1154,13 b' The full set of options is:'
     be present in this list. The contents of the allow_push list are
     examined after the deny_push list.
 
+``guessmime``
+    Control MIME types for raw download of file content.
+    Set to True to let hgweb guess the content type from the file
+    extension. This will serve HTML files as ``text/html`` and might
+    allow cross-site scripting attacks when serving untrusted
+    repositories. Default is False.
+   
 ``allow_read``
     If the user has not already been denied repository access due to
     the contents of deny_read, this list determines whether to grant

mercurial/hgweb/webcommands.py

@@ -32,6 +32,8 b' def log(web, req, tmpl):'
         return changelog(web, req, tmpl)
 
 def rawfile(web, req, tmpl):
+    guessmime = web.configbool('web', 'guessmime', False)
+
     path = webutil.cleanpath(web.repo, req.form.get('file', [''])[0])
     if not path:
         content = manifest(web, req, tmpl)
@@ -50,9 +52,11 b' def rawfile(web, req, tmpl):'
 
     path = fctx.path()
     text = fctx.data()
+    mt = 'application/binary'
+    if guessmime:
     mt = mimetypes.guess_type(path)[0]
     if mt is None:
-        mt = binary(text) and 'application/octet-stream' or 'text/plain'
+            mt = binary(text) and 'application/binary' or 'text/plain'
     if mt.startswith('text/'):
         mt += '; charset="%s"' % encoding.encoding
 

tests/test-hgweb-raw.t

@@ -22,6 +22,28 b' Test raw style of hgweb'
   $ sleep 1 # wait for server to scream and die
   $ cat getoutput.txt
   200 Script output follows
+  content-type: application/binary
+  content-length: 157
+  content-disposition: inline; filename="some \"text\".txt"
+  
+  This is just some random text
+  that will go inside the file and take a few lines.
+  It is very boring to read, but computers don't
+  care about things like that.
+  $ cat access.log error.log
+  127.0.0.1 - - [*] "GET /?f=a23bf1310f6e;file=sub/some%20%22text%22.txt;style=raw HTTP/1.1" 200 - (glob)
+
+  $ rm access.log error.log
+  $ hg serve -p $HGPORT -A access.log -E error.log -d --pid-file=hg.pid \
+  > --config web.guessmime=True
+
+  $ cat hg.pid >> $DAEMON_PIDS
+  $ ("$TESTDIR/get-with-headers.py" localhost:$HGPORT '/?f=a23bf1310f6e;file=sub/some%20%22text%22.txt;style=raw' content-type content-length content-disposition) >getoutput.txt &
+  $ sleep 5
+  $ kill `cat hg.pid`
+  $ sleep 1 # wait for server to scream and die
+  $ cat getoutput.txt
+  200 Script output follows
   content-type: text/plain; charset="ascii"
   content-length: 157
   content-disposition: inline; filename="some \"text\".txt"