I'm a complete n00b to C and have tried googling the errors, but haven't been able to figure out what to change for this to work. I'm trying to compile an exploitdb .c file (764.c). Following this guide, I've made all the changes, but it still won't compile.
Error:
$gcc exploit2.c -o 764 -lcrypto
exploit2.c: In function ‘send_ssl_packet’:
exploit2.c:641:27: error: assignment of read-only location ‘*p’
641 | #define s2n(s,c) ((c[0]=(unsigned char)(((s)>> 8)&0xff), c[1]=(unsigned char)(((s) )&0xff)),c+=2)
| ^
exploit2.c:908:2: note: in expansion of macro ‘s2n’
908 | s2n(tot_len, p);
| ^~~
exploit2.c:641:65: error: assignment of read-only location ‘*(p + 1)’
641 | #define s2n(s,c) ((c[0]=(unsigned char)(((s)>> 8)&0xff), c[1]=(unsigned char)(((s) )&0xff)),c+=2)
| ^
exploit2.c:908:2: note: in expansion of macro ‘s2n’
908 | s2n(tot_len, p);
| ^~~
exploit2.c:920:13: warning: passing argument 1 of ‘MD5_Final’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
920 | MD5_Final(p, &ctx);
| ^
In file included from exploit2.c:27:
/usr/include/openssl/md5.h:42:30: note: expected ‘unsigned char *’ but argument is of type ‘const unsigned char *’
42 | int MD5_Final(unsigned char *md, MD5_CTX *c);
| ~~~~~~~~~~~~~~~^~
exploit2.c:924:10: warning: passing argument 1 of ‘memcpy’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
924 | memcpy(p, rec, rec_len);
| ^
In file included from exploit2.c:17:
/usr/include/string.h:43:14: note: expected ‘void * restrict’ but argument is of type ‘const unsigned char *’
43 | extern void *memcpy (void *__restrict __dest, const void *__restrict __src,
| ^~~~~~
exploit2.c:931:10: warning: passing argument 1 of ‘memcpy’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
931 | memcpy(p, rec, rec_len);
| ^
In file included from exploit2.c:17:
/usr/include/string.h:43:14: note: expected ‘void * restrict’ but argument is of type ‘const unsigned char *’
43 | extern void *memcpy (void *__restrict __dest, const void *__restrict __src,
Any help would be greatly appreciated.
It seems like you have made a mistake when applying Step 3 Insert “const”
// unsigned char *p, *end;
const unsigned char *p, *end;
The code contains declarations of unsigned char *p in three different places and you modified the wrong one to be const, with the errors and warnings that you showed as the consequence. Only the one in the function get_server_hello() should be changed.
By the way, At the top of 764 it says there is an update to it, 47080. The latter has all the modifications (and more) applied already and builds fine with OpenSSL 1.1.1d.