one-byte-heap-overread (wolfcrypt/src/asn.c:7584)

[flyroom]

tested on wolfSSL 4.1.0 / ubuntu 14.04/ clang / asan
Hi, I've came upon an one-byte-heap-overread bug
due to corner case mishandling in GetLength_ex(wolfcrypt/src/asn.c:189), you could trigger it by loading attached DER certificate using API wolfSSL_X509_d2i (or example_cert_parsing_app) (test_crt.zip)
Corner cases:

if (check && (**idx + length**) > maxIdx) {   /* for user of length */

      WOLFSSL_MSG("GetLength value exceeds buffer length");

      return BUFFER_E;

  }

If idx + length == maxIdx which passed the check, it will trigger a buffer over read in (wolfcrypt/src/asn.c:7584)

if (**input[idx]** == ASN_BOOLEAN) {
            ret = GetBoolean(input, &idx, sz);
            if (ret < 0) {
                WOLFSSL_MSG("\tfail: critical boolean");
                return ret;
            }

            critical = (byte)ret;
        }

ASAN report

==49107==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x61900000048f at pc 0x7f755c0cd6cc bp 0x7ffce2a2cc00 sp 0x7ffce2a2cbf8
READ of size 1 at 0x61900000048f thread T0
    #0 0x7f755c0cd6cb in DecodeCertExtensions wolfcrypt/src/asn.c:7584
    #1 0x7f755c0cd6cb in ParseCertRelative wolfcrypt/src/asn.c:8174
    #2 0x7f755c062097 in wolfSSL_X509_d2i src/ssl.c:15361
    #3 0x7f755c04b685 in main (/opt/disk/wolfSSL_X509_d2i_gcc+0x1e685)
    #4 0x7f755ad94f44 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21f44)
    #5 0x7f755c04b2eb  (/opt/disk/wolfSSL_X509_d2i_gcc+0x1e2eb)

0x61900000048f is located 0 bytes to the right of 1039-byte region [0x619000000080,0x61900000048f)
allocated by thread T0 here:
    #0 0x7f755b4fc479 in __interceptor_malloc /home/nwani/m3/conda-bld/compilers_linux-64_1560109574129/work/.build/x86_64-conda_cos6-linux-gnu/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:144
    #1 0x7f755c04b5aa in main (/opt/disk/wolfSSL_X509_d2i_gcc+0x1e5aa)
    #2 0x7f755ad94f44 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21f44)

SUMMARY: AddressSanitizer: heap-buffer-overflow wolfcrypt/src/asn.c:7584 in DecodeCertExtensions
Shadow bytes around the buggy address:
  0x0c327fff8040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c327fff8050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c327fff8060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c327fff8070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c327fff8080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c327fff8090: 00[07]fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c327fff80a0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c327fff80b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c327fff80c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c327fff80d0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c327fff80e0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represen
[test_crt.zip](https://github.com/wolfSSL/wolfssl/files/3524394/test_crt.zip)

ts 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
==49107==ABORTING

[JacobBarthelmeh]

Hi @flyroom,

Thank you for the report!

I created a PR (#2425) that does a check on the buffer before reading the ASN_BOOLEAN byte. The ASAN I have on my development system was not reporting the issue but printing out the values when running the test case it does look like it is accessing one index over.

$ ./a.out 
idx = 135 sz = 135

Am considering a PR also for the GetLength check. Can you tell us some about your project? And if you send a mailing address to our support (at) wolfssl we would like to send you some swag.

Regards,
Jacob