git-fast-import segfaults

[cpettitt <cpettitt@gmail.com>]

I'm seeing the following errors when I run git-fast-import (on Intel
OSX) with some data from a git-p4 import:

[cpettitt@gish scratch2]$ rm -rf .git; git init; git-fast-import < ~/writer.out
Initialized empty Git repository in .git/
git-fast-import(23021) malloc: *** error for object 0x500e50: double free
git-fast-import(23021) malloc: *** set a breakpoint in szone_error to debug
git-fast-import(23021) malloc: ***  Deallocation of a pointer not
malloced: 0x501a80; This could be a double free(), or free() called
with the middle of an allocated block; Try setting environment
variable MallocHelp to see tools to help debug
git-fast-import(23021) malloc: *** error for object 0x5020a0: double free
git-fast-import(23021) malloc: *** set a breakpoint in szone_error to debug
git-fast-import(23021) malloc: ***  Deallocation of a pointer not
malloced: 0x5007e0; This could be a double free(), or free() called
with the middle of an allocated block; Try setting environment
variable MallocHelp to see tools to help debug
git-fast-import(23021) malloc: ***  Deallocation of a pointer not
malloced: 0x5006e0; This could be a double free(), or free() called
with the middle of an allocated block; Try setting environment
variable MallocHelp to see tools to help debug
git-fast-import(23021) malloc: ***  Deallocation of a pointer not
malloced: 0x501e10; This could be a double free(), or free() called
with the middle of an allocated block; Try setting environment
variable MallocHelp to see tools to help debug
git-fast-import(23021) malloc: ***  Deallocation of a pointer not
malloced: 0x502190; This could be a double free(), or free() called
with the middle of an allocated block; Try setting environment
variable MallocHelp to see tools to help debug
git-fast-import(23021) malloc: *** error for object 0x500280: double free
git-fast-import(23021) malloc: *** set a breakpoint in szone_error to debug
git-fast-import(23021) malloc: ***  Deallocation of a pointer not
malloced: 0x5009c0; This could be a double free(), or free() called
with the middle of an allocated block; Try setting environment
variable MallocHelp to see tools to help debug
git-fast-import(23021) malloc: *** error for object 0x500b00:
incorrect checksum for freed object - object was probably modified
after being freed, break at szone_error to debug
git-fast-import(23021) malloc: *** set a breakpoint in szone_error to debug
Segmentation fault

I start getting free errors at fast-import.c:1577:

                        rc = rc_free;
                        if (rc)
                                rc_free = rc->next;
                         else {
                                rc = cmd_hist.next;
                                cmd_hist.next = rc->next;
                                cmd_hist.next->prev = &cmd_hist;
                                free(rc->buf); // <-- error is emitted
in free here
                        }


I believe these errors started showing up in commit
b449f4cfc972929b638b90d375b8960c37790618. I did a bisect on
fast-import.c and this was the first commit for that file that
exhibits this bug with the input.

I thought I would check with the list to see if this is a known issue
before I spend time trying to dig into it.