Patch applies fake diffs from commit messages(samizdat.dev) |
Patch applies fake diffs from commit messages(samizdat.dev) |
This wouldn't be an issue if patches were XML or JSON with a well defined schema, but everything must be a boutique undocumented format in the world of Unix tools.
Maybe the worst part about this is that it can entirely come from a patch being exported by git and then imported straight back in to git. If you can't even handle your own undocumented format then what hope do other tools have that want to work with it?
Git recently added this doc on roundtripping, and the problem is with git.
Any line that is of the form:
* three-dashes and end-of-line, or
* a line that begins with "diff -", or
* a line that begins with "Index: "
is taken as the beginning of a patch, and the commit log message is terminated before the first occurrence of such a line.
The argument is if git should do input sanitation etc...
But `patch -p1` is doing exactly what was documented, even in the original Larry Wall usenet post of the program.
[0] https://pubs.opengroup.org/onlinepubs/9799919799/utilities/p... [1] https://github.com/git/git/blob/94f057755b7941b321fd11fec1b2...
Patch files are readable by humans. Replacing them with XML or JSON would fix this problem, but at the expense of removing a core feature.
Or, more snarky: tee is also a huge security problem if you pipe untrusted input into `tee -a /etc/passwd`, such as `curl | tee -a /etc/passwd`. Not many things are safe with a `curl |` in front of them. I think yes might be?
No one wants to apply diffs in commit messages. But some people use this technique via email:
Finally fix it
---
Changes in v2:
- Proper formatting
- Remove irrelevant typo fix
I would personally use Git notes instead though.
Finally fix it
---
Notes:
Changes in v2: ...Or MIME, even.
If the point is to be able to do `curl https://...deadbeef.patch | patch -p1`, you can just change the extension provided to Github from `.patch` to `.diff`. That way, it just includes the hunks. E.g.
https://github.com/torvalds/linux/commit/dca922e019dd758b4c1...
I don't see it as a problem with the email format, because I can't imagine someone just patching from an email without looking at the email first.
This is Re:
> I do not yet know whether the bug belongs to GNU patch, GitHub’s .patch export, or the broader patch-format contract.
I don't think this is a problem with GNU patch or the patch format per se, just the emailed commit format. I think the patch format's good because it allows it to be embedded in other texts and also allows comments or extended syntax between hunks. For example, the lines
diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 15ba592236e845..725a49a0eee72e 100644
Simply changing `git-am` to accept commit messages being indented in the email format would allow Github fix the issue of their .patch exports being incompatible with `patch`, in addition to fixing that bug about commit messages being truncated when they have a `---` line.
In any case, agreed that it's not a great "feature" to use in-band signaling of when patch data starts, with no escaping. Confusion and misbehavior is pretty much guaranteed.
This means that it will try to apply any unindented diffs in the commit message. But you’re fine if you indent the diff. (Newschool code fencers will have a worse time here.)
I imagine that this worked fine for changes that were authored by one person and submitted by another person via email, or by their friend, or by someone trying to resurrect a previous attempt at getting something upstreamed. Someone is likely to notice that examples diffs are getting applied. But it won’t work well at all if you are some software distributor who is using patch files to apply modifications to packages.
Recall that git-am(1) will not apply indented diffs. Well have a look at my GNU patch 2.7.6:
If the entire diff is indented by a consistent amount, if lines end in
CRLF, or if a diff is encapsulated one or more times by prepending "- "
to lines starting with "-" as specified by Internet RFC 934, this is
taken into account.
Larry Wall wrote the original version of patch.
Imagine the diff only has
if (someIntParamThatShouldHaveBeenUInt < 0)
throw new ArgumentOutOfRangeException();
Not sure why somebody thought it was a good idea. There probably was a use case at some point where it seemed smart to allow for things like this. Maybe it’s for CI, but I really can’t think of why.
But I really doubt this could be a bug. I mean why would patch even need to read the commit message if it wasn’t to scan it for diff?
Andreas Gruenbacher is active currently. Or git can change to differentiate the message prefix better
This would be "solved" if the patch file only included the patch. That's pretty straightforward. The file github provides includes fake email headers for no particular reason. The commit message appears to be part of the subject header. The subject header is never terminated, so arguably applying this patch shouldn't do anything. (Because the actual patch data is also part of the email headers.) The other headers aren't terminated either, so actually there is no subject header. This shouldn't really matter, because the patch file isn't email, but it does seem to want to pretend to be.
The usual question to ask here would be "why are you applying patch files from an untrusted source?". If patch(1) was stricter about the format of its input files... applying patches from an untrusted source would still be a good way to get owned. If you think I can get you to patch inappropriate files by writing a fake diff into my commit message... wait until you see what I can do by writing those same changes into the real diff.
That's the output you get from `git format-patch --stdout -1 dd28283`. The idea is that it's suitable for emailing to a mailing list for review (hence the subject line beginning with [PATCH], and so on).
If you ask for colorized output with `git format-patch --color=always --stdout -1 dd28283` you'll see that `git format-patch` itself knows which bits are the commit message and which bits are the diff. (Well, of course it does, I guess.)
I suspect that if you sent a patch like this to the mailing list, they'd get mad at you. So `git format-patch` is working OK for its intended use-case. Arguably it's GitHub causing the problem here by "misusing" `git format-patch` as a way to deliver patches that are (these days) expected to be machine-readable — something you can just curl and pipe into `patch`. `git format-patch` doesn't do that.
That said, yeah, it's amusing that (as TFA says)
git format-patch -1 HEAD --stdout > 0001 ;
git checkout HEAD~ ;
git am 0001
> If you think I can get you to patch inappropriate files by writing a fake diff into my commit message... wait until you see what I can do by writing those same changes into the real diff.
Well put. :)
Therefore I retract my claim that this is even a "misuse" of `git format-patch` by GitHub. Seems like GitHub provides both a git-am-able endpoint and a (less exploitable) patch-able endpoint, and the issue is just that OP chose the less suitable one of those two endpoints.
It doesn't comply with RFC 5322 ( https://www.rfc-editor.org/rfc/rfc5322#section-2.2 ), which requires that email headers terminate in CRLF.
<?xml version="1.0" encoding="UTF-8"?> <claims> <claims_I_did_not_make description='Claims that I did not make or defend.'> <claim>Patch is perfect.</claim> <claim>Ambiguity is good.</claim> <claim>There are no better formats for conveying patches.</claim> </claims_I_did_not_make> <claims_I_did_make description='What I actually said.'> <claim>Patch files are readable by humans.</claim> <claim>Being readble by humans is useful.</claim> <claim>XML is painful for humans to read and write.</claim> <claim>JSON is painful for humans to read and write.</claim> <claim caveat='Actually this would require all parties to handle JSON or XML correctly which on further reflection I am not sure about. Still, it is a claim I initially made.'>JSON or XML would actually fix this problem in the format.</claim> </claims_I_did_make> <claims_I_did_not_make_but_am_open_to description='Things that were never specified but that I do not actually disagree with.'> <claim>The patch format could be improved.</claim> <claim>Formats should be unambiguous.</claim> <claim>Separating sections is good.</claim> </claims_I_did_not_make_but_am_open_to> </claims> <?xml version="1.0" encoding="UTF-8"?>
<claims>
<claims_I_did_not_make description='Claims that I did not make or defend.'>
<claim>Patch is perfect.</claim>
<claim>Ambiguity is good.</claim>
<claim>There are no better formats for conveying patches.</claim>
</claims_I_did_not_make>
<claims_I_did_make description='What I actually said.'>
<claim>Patch files are readable by humans.</claim>
<claim>Being readble by humans is useful.</claim>
<claim>XML is painful for humans to read and write.</claim>
<claim>JSON is painful for humans to read and write.</claim>
<claim caveat='Actually this would require all parties to handle JSON or XML correctly which on further reflection I am not sure about. Still, it is a claim I initially made.'>JSON or XML would actually fix this problem in the format.</claim>
</claims_I_did_make>
<claims_I_did_not_make_but_am_open_to description='Things that were never specified but that I do not actually disagree with.'>
<claim>The patch format could be improved.</claim>
<claim>Formats should be unambiguous.</claim>
<claim>Separating sections is good.</claim>
</claims_I_did_not_make_but_am_open_to>
</claims>> XML is painful for humans to read and write.
Speaking of claims no-one made; no-one's talking about writing patch files by hand.
People do write patch files be hand.
Tons of bugs in scripting in Unix come from the fact that data and metadata are interspersed in the same stream (you can mitigate somewhat with stderr vs stdout but hardly anyone does). Examples include things like trying to handle random filenames from * expansions.
It’s a bit more annoying to deal with sometimes, but for actual scripts it’s much more foolproof.
xargs is one of the programs that is designed to work around the original issue.
you may enjoy these recent comments about better terminals:
https://news.ycombinator.com/item?id=47812724
So many problems are avoided, but at the same time the Windows ecosystem is just so far from providing an properly usable terminal experience. Things are still really not designed to be used from PowerShell.