Gcc 8 warns on buffer truncation

Description of problem:

Found a bug in the parser for Gnu libtasn1-4.9, they in the case of making the tokens and by that adding a "-" to the string go over the length of their buffer. So the problem is using a sizeof on the buffer size and making the buffer too short. Looks like two problems, this way the problem creeps as you grow the buffer to add room for the "-":

Version of libtasn1 used:

Gnu 1-4.9

Distributor of libtasn1 (e.g., Ubuntu, Fedora, RHEL)

Gnu source tarball.

How reproducible:

Compile using Gcc 8 using -Werror=format-truncation

Steps to Reproduce:

• one

Unpack tarball and run configure, please see attached config.status.

• two

Make using those flags.

• three

See Gcc flag the error as follows:

Actual results:

GNU C17 (GCC) version 8.2.0 (x86_64-pc-linux-gnu)
	compiled by GNU C version 8.2.0, GMP version 6.1.2, MPFR version 4.0.1, MPC version 1.1.0, isl version none
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 81f798d4ff0871f00b0a4f3f1296b20a
ASN1.c: In function '_asn1_yyparse':
ASN1.y:164:47: error: 'snprintf' output may be truncated before the last format character [-Werror=format-truncation=]
                 | '-' NUM        {snprintf($$,sizeof($$),"-%s",$2);}
                                               ^~~~~
ASN1.y:164:6: note: 'snprintf' output between 2 and 66 bytes into a destination of size 65
                 | '-' NUM        {snprintf($$,sizeof($$),"-%s",$2);}
      ^          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ASN1.y:152:47: error: 'snprintf' output may be truncated before the last format character [-Werror=format-truncation=]
 neg_num : '-' NUM     {snprintf($$,sizeof($$),"-%s",$2);}
                                               ^~~~~
ASN1.y:152:6: note: 'snprintf' output between 2 and 66 bytes into a destination of size 65
 neg_num : '-' NUM     {snprintf($$,sizeof($$),"-%s",$2);}
      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~          
cc1: all warnings being treated as errors
Makefile:1112: recipe for target 'ASN1.lo' failed

Please see:

config.status

gcc_v.txt

Expected results:

No warning or errors.