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

"Philip Oakley" [off-list ref] writes:

From: "Junio C Hamano" <redacted>

quoted

Stefan Naewe [off-list ref] writes:

quoted

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.