Crash: Initialize Decimal with itself triggers an assertion

When `Decimal` is initialized with itself, a new (empty) `mpd_t` will be created. To fill it with a value, `to_s` of the current instance is called, which accesses the empty `mpd_t`. This triggers an assertion, which leads to a crash. # Patch I've created and attached a simple patch which just returns self when a Decimal is initialized with itself. Pretty simple, but should do the job (careful: I've created the patch after a 20h flight, could be... uhm, suboptimal). # PoC PoC does work on `https://www.mruby.science/runs`, but as it's not up2date that shouldn't really mean anything. ``` a = Decimal.new a.initialize a ``` # Trace ``` $ gdb attach 10251 GNU gdb (GDB) 7.12 Copyright (C) 2016 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "x86_64-pc-linux-gnu". Type "show configuration" for configuration details. For bug reporting instructions, please see: <http://www.gnu.org/software/gdb/bugs/>. Find the GDB manual and other documentation resources online at: <http://www.gnu.org/software/gdb/documentation/>. For help, type "help". Type "apropos word" to search for commands related to "word"... attach: No such file or directory. Attaching to process 10251 Reading symbols from /home/simon/git/shopify/mruby-engine/ext/mruby_engine/mruby/build/host/bin/mirb...done. Reading symbols from /usr/lib/libm.so.6...(no debugging symbols found)...done. Reading symbols from /usr/lib/libreadline.so.7...(no debugging symbols found)...done. Reading symbols from /usr/lib/libncursesw.so.6...(no debugging symbols found)...done. Reading symbols from /usr/lib/libc.so.6...(no debugging symbols found)...done. Reading symbols from /lib64/ld-linux-x86-64.so.2...(no debugging symbols found)...done. 0x00007f8de487f131 in pselect () from /usr/lib/libc.so.6 (gdb) c Continuing. Program received signal SIGABRT, Aborted. 0x00007f8de47d104f in raise () from /usr/lib/libc.so.6 (gdb) bt #0 0x00007f8de47d104f in raise () from /usr/lib/libc.so.6 #1 0x00007f8de47d247a in abort () from /usr/lib/libc.so.6 #2 0x00007f8de47c9ea7 in __assert_fail_base () from /usr/lib/libc.so.6 #3 0x00007f8de47c9f52 in __assert_fail () from /usr/lib/libc.so.6 #4 0x000000000045a356 in mpd_msword (dec=0xa75980) at /home/simon/git/shopify/mruby-engine/ext/mruby_engine/mruby-mpdecimal/src/mpdecimal.c:218 #5 mpd_iszero (dec=dec@entry=0xa75980) at /home/simon/git/shopify/mruby-engine/ext/mruby_engine/mruby-mpdecimal/src/mpdecimal.c:331 #6 0x0000000000472fc0 in mpd_qformat_spec (dec=dec@entry=0xa75980, spec=spec@entry=0x7ffc8fdcd220, ctx=ctx@entry=0x9f8580, status=status@entry=0x7ffc8fdcd28c) at /home/simon/git/shopify/mruby-engine/ext/mruby_engine/mruby-mpdecimal/src/io.c:1320 #7 0x00000000004738d5 in mpd_qformat (dec=0xa75980, fmt=fmt@entry=0x481177 "f", ctx=0x9f8580, status=status@entry=0x7ffc8fdcd28c) at /home/simon/git/shopify/mruby-engine/ext/mruby_engine/mruby-mpdecimal/src/io.c:1390 #8 0x000000000045602a in ext_decimal_to_s (state=0x9b1010, rself=...) at /home/simon/git/shopify/mruby-engine/ext/mruby_engine/mruby-mpdecimal/src/ext.c:220 #9 0x000000000040f6af in mrb_funcall_with_block (mrb=mrb@entry=0x9b1010, self=..., mid=<optimized out>, mid@entry=38, argc=<optimized out>, argc@entry=0, argv=argv@entry=0x0, blk=..., blk@entry=...) at /home/simon/git/shopify/mruby-engine/ext/mruby_engine/mruby/src/vm.c:407 #10 0x000000000040fbcc in mrb_funcall_argv (mrb=mrb@entry=0x9b1010, self=..., self@entry=..., mid=mid@entry=38, argc=argc@entry=0, argv=argv@entry=0x0) at /home/simon/git/shopify/mruby-engine/ext/mruby_engine/mruby/src/vm.c:424 #11 0x0000000000403d23 in convert_type (raise=1 '\001', method=0x4810cd "to_s", tname=0x4813ea "String", val=..., mrb=0x9b1010) at /home/simon/git/shopify/mruby-engine/ext/mruby_engine/mruby/src/object.c:316 #12 mrb_convert_type (mrb=mrb@entry=0x9b1010, val=..., type=type@entry=MRB_TT_STRING, tname=tname@entry=0x4813ea "String", method=method@entry=0x4810cd "to_s") at /home/simon/git/shopify/mruby-engine/ext/mruby_engine/mruby/src/object.c:338 #13 0x0000000000455927 in ext_decimal_initialize (state=0x9b1010, self=...) at /home/simon/git/shopify/mruby-engine/ext/mruby_engine/mruby-mpdecimal/src/ext.c:86 #14 0x000000000041150f in mrb_vm_exec (mrb=mrb@entry=0x9b1010, proc=<optimized out>, proc@entry=0x9b9020, pc=<optimized out>) at /home/simon/git/shopify/mruby-engine/ext/mruby_engine/mruby/src/vm.c:1165 #15 0x0000000000416d57 in mrb_vm_run (mrb=mrb@entry=0x9b1010, proc=proc@entry=0x9b9020, self=..., stack_keep=stack_keep@entry=2) at /home/simon/git/shopify/mruby-engine/ext/mruby_engine/mruby/src/vm.c:766 #16 0x00000000004028be in main (argc=<optimized out>, argv=<optimized out>) at /home/simon/git/shopify/mruby-engine/ext/mruby_engine/mruby/mrbgems/mruby-bin-mirb/tools/mirb/mirb.c:549 (gdb) info registers rax 0x0 0 rbx 0x6 6 rcx 0x7f8de47d104f 140247400517711 rdx 0x0 0 rsi 0x7ffc8fdccc30 140722722098224 rdi 0x2 2 rbp 0x4ac565 0x4ac565 rsp 0x7ffc8fdccca8 0x7ffc8fdccca8 r8 0x0 0 r9 0x7ffc8fdccc30 140722722098224 r10 0x8 8 r11 0x246 582 r12 0xda 218 r13 0x4acbb8 4901816 r14 0x0 0 r15 0x7ffc8fdcd220 140722722099744 rip 0x7f8de47d104f 0x7f8de47d104f <raise+207> eflags 0x246 [ PF ZF IF ] cs 0x33 51 ss 0x2b 43 ds 0x0 0 es 0x0 0 fs 0x0 0 gs 0x0 0 (gdb) ```