From: Konstantin Ryabitsev <konstantin@linuxfoundation.org>
To: git@vger.kernel.org
Subject: git-patch-id and syntactically significant whitespace
Date: Mon, 10 Feb 2020 11:41:15 -0500 [thread overview]
Message-ID: <20200210164115.x4gciujyjisivfgi@chatter.i7.local> (raw)
Hello:
Git patch-id is often used as convenient way to represent patches based
on their content. It accomplishes this by attempting to normalize a
patch before producing a hash of the result -- most notably, by trimming
a lot of whitespace.
Unfortunately, this does not work well with syntactically-significant
whitespace languages, notably Python and Make. For example, the
following two patches produce identical patch-id's, but one of them is
actually malicious.
Benign:
diff --git a/file1.py b/file1.py
index e574c49..6aa1937 100644
--- a/file1.py
+++ b/file1.py
@@ -1,3 +1,13 @@
#!/usr/bin/python
+def is_logged_in(cookie):
+ if cookie:
+ print('User is logged in')
+ return True
+
+ return False
+
+if is_logged_in(True):
+ print('You are logged in')
+
print('Hello!')
Malicious ("return True" is unindented, which results in is_logged_in()
always returning "True"):
diff --git a/file1.py b/file1.py
index e574c49..6aa1937 100644
--- a/file1.py
+++ b/file1.py
@@ -1,3 +1,13 @@
#!/usr/bin/python
+def is_logged_in(cookie):
+ if cookie:
+ print('User is logged in')
+ return True
+
+ return False
+
+if is_logged_in(True):
+ print('You are logged in')
+
print('Hello!')
This mostly becomes a problem if we try to build any kind of patch
indexing/retrieval systems that rely on patch-id to identify patches.
While this is not a high-impact problem by any means, it's not a
theoretical concern: git-format-patch includes functionality to provide
patch dependencies via prerequisite-patch-id trailers [1]. An automated
system attempting to auto-fetch dependencies can potentially retrieve
and apply the malicious version of the patch.
I'm not sure what the solution here is, since changing git-patch-id to
not discard whitespace is obviously going to defeat its entire purpose
of "not ever changing". I mostly wanted to share my findings in case
someone has thoughts on how to best approach this.
-K
[1] https://git-scm.com/docs/git-format-patch#_base_tree_information
next reply other threads:[~2020-02-10 16:41 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-10 16:41 Konstantin Ryabitsev [this message]
2020-02-10 22:24 ` git-patch-id and syntactically significant whitespace Jeff King
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