threads / discuss / 12502

git-log segfault on 00 graft

Subject: git-log segfault on 00 graft

## tl;dr

5 messages between Mar 4, 2008 and Mar 5, 2008.

replies: 4people: 4as markdown or json

Jan Engelhardt· Mar 4, 2008, 18:57 UTC · lore

Hi,

I was playing a bit with grafts, and actually did this:

  echo '839affa3313011da783b5b8074a5c9805ee8503a 
0000000000000000000000000000000000000000' >.git/info/grafts

running `git log --topo-order` causes a segfault. Yes, I probably "should not be doing that", but I think it at least should not segfault.

Johannes Schindelin· Mar 4, 2008, 19:09 UTC · re: Jan Engelhardt · lore

Re: git-log segfault on 00 graft

Hi,

On Tue, 4 Mar 2008, Jan Engelhardt wrote:

Show 8 quoted lines

> I was playing a bit with grafts, and actually did this:
> 
>   echo '839affa3313011da783b5b8074a5c9805ee8503a 
> 0000000000000000000000000000000000000000' >.git/info/grafts
> 
> running `git log --topo-order` causes a segfault. Yes, I probably 
> "should not be doing that", but I think it at least should not
> segfault.

Well, I agree with the first, but not the latter. grafts are a really core and plumbing thing, and if you set it to something nonsensical, I think you should expect something like a segmentation fault.

Ciao, Dscho

Shawn O. Pearce· Mar 5, 2008, 05:06 UTC · re: Johannes Schindelin · lore

Re: git-log segfault on 00 graft

Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:

Show 14 quoted lines

> On Tue, 4 Mar 2008, Jan Engelhardt wrote:
> 
> > I was playing a bit with grafts, and actually did this:
> > 
> >   echo '839affa3313011da783b5b8074a5c9805ee8503a 
> > 0000000000000000000000000000000000000000' >.git/info/grafts
> > 
> > running `git log --topo-order` causes a segfault. Yes, I probably 
> > "should not be doing that", but I think it at least should not
> > segfault.
> 
> Well, I agree with the first, but not the latter.  grafts are a really 
> core and plumbing thing, and if you set it to something nonsensical, I 
> think you should expect something like a segmentation fault.

I'm sorry, I don't know where you learned to program Dscho, but my mentors always taught me that user input should be handled with care, and SIGSEGV / SIGBUS / SIGILL is not handling with care!

We tell users to popuate the .git/info/grafts file. By hand. Its user input. We shouldn't segfault over a malformed entry.

-- 
Shawn.

Johannes Schindelin· Mar 5, 2008, 12:43 UTC · re: Shawn O. Pearce · lore

Re: git-log segfault on 00 graft

Hi,

On Wed, 5 Mar 2008, Shawn O. Pearce wrote:

Show 19 quoted lines

> Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:
> > On Tue, 4 Mar 2008, Jan Engelhardt wrote:
> > 
> > > I was playing a bit with grafts, and actually did this:
> > > 
> > >   echo '839affa3313011da783b5b8074a5c9805ee8503a 
> > > 0000000000000000000000000000000000000000' >.git/info/grafts
> > > 
> > > running `git log --topo-order` causes a segfault. Yes, I probably 
> > > "should not be doing that", but I think it at least should not 
> > > segfault.
> > 
> > Well, I agree with the first, but not the latter.  grafts are a really 
> > core and plumbing thing, and if you set it to something nonsensical, I 
> > think you should expect something like a segmentation fault.
> 
> I'm sorry, I don't know where you learned to program Dscho, but my 
> mentors always taught me that user input should be handled with care, 
> and SIGSEGV / SIGBUS / SIGILL is not handling with care!

I agree.

> We tell users to popuate the .git/info/grafts file.  By hand.
> Its user input.  We shouldn't segfault over a malformed entry.

Well, I disagree about the user input. .git/info/grafts can break tons of things, just by _existing_. So you definitely need to know what you are doing.

Just inserting random strings into the grafts file is not an option. It is not something that we should take pains to catch... just like a Unix system does not prevent "rm -rf /" as root.

So again, I do think that a segmentation fault is not good. But I disagree that you have to go to great lengths to prevent a segmentation fault when a user is fiddling with internals without even knowing what could happen.

IOW in this case, the _user input_ would have better been crafted with care, and it was clearly not.

But as has been pointed out, the segfault has been already fixed (most likely by one of Martin's patches), so the discussion about this particular problem is moot.

Ciao, Dscho

Björn Steinbrink· Mar 5, 2008, 05:27 UTC · re: Jan Engelhardt · lore

Re: git-log segfault on 00 graft

On 2008.03.04 19:57:42 +0100, Jan Engelhardt wrote:

Show 11 quoted lines

> Hi,
> 
> 
> I was playing a bit with grafts, and actually did this:
> 
>   echo '839affa3313011da783b5b8074a5c9805ee8503a 
> 0000000000000000000000000000000000000000' >.git/info/grafts
> 
> running `git log --topo-order` causes a segfault. Yes, I probably 
> "should not be doing that", but I think it at least should not
> segfault.

error: Could not read 0000000000000000000000000000000000000000 fatal: revision walk setup failed

That's what I get with a somewhat up-to-date version from master.

Björn