Re: [PATCH] revision.c: fix possible null pointer access

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"Philip Oakley" <philipoakley@xxxxxxx> writes:

> From: "Junio C Hamano" <gitster@xxxxxxxxx>
>> Stefan Naewe <stefan.naewe@xxxxxxxxx> writes:
>>
>>> Two functions dereference a tree pointer before checking
>>
>> Reading them a bit carefully, a reader would notice that they
>> actually do not dereference the pointer at all.  It just computes
>> another pointer and that is done by adding the offset of object
>> member in the tree struct.
>
> But you can't do that computation (in the error case under
> consideration). Null can't be added to anything (as far as the
> implications of the standards go). These are horrid gotchas because
> they go against the grain of all that binary arithmetic and
> simplifications we learnt long ago.

Yeah, but in that hunk that does check !tree, because the function
can be fed a NULL, the computed result assigned to object, which is
undefined, is never used ;-)

Of course, there used to be exotic platforms that are still standard
compliant that triggered a trap when such a pointer computation was
made (rather, such a bogus pointer was assigned to a pointer
variable).  I do not think anybody attempted to port Git to such a
platform, but I agree that it is better to "fix" such a codepath, if
only to stop wasting time dealing with them discussing with language
lawyers ;-)

So as I said in my review, the first hunk is a reject, the second
one is OK.

Thanks.
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