How to detect buffer overflow in C for this particular case, - c

Question

I think this code should produce a buffer overflow error but apparently, this prints fine.. is there anyway to detect it has overflown?
Valgrind didn't picked it up either...
static void e(void) {
char buffer[5];
char data1[] = "abc";
char data2[] = "de";
memcpy(buffer, data1, sizeof(data1));
// strcat appends data2 to buffer and adds '\0' at the end dest
strcat(buffer, data2);
//printf("%s\n", buffer);
}

Answer 1

The -fsanitize=address of gcc is the option you're looking for. E.g.:
$ cat test.cpp
#include <stdio.h>
#include <string.h>
static void e(void) {
char buffer[5];
char data1[] = "abc";
char data2[] = "de";
memcpy(buffer, data1, sizeof(data1));
// strcat appends data2 to buffer and adds '\0' at the end dest
strcat(buffer, data2);
//printf("%s\n", buffer);
}
int main() {
e();
}
$ g++ test.cpp -o a -fsanitize=address -g3
$ ./a
=================================================================
==21537== ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffd1d8c0313 at pc 0x7f96ebedd94b bp 0x7ffd1d8c0260 sp 0x7ffd1d8bfa20
WRITE of size 3 at 0x7ffd1d8c0313 thread T0
#0 0x7f96ebedd94a (/usr/lib/x86_64-linux-gnu/libasan.so.0.0.0+0xe94a)
#1 0x40091b (/tmp/a+0x40091b)
#2 0x400959 (/tmp/a+0x400959)
#3 0x7f96ebb2bec4 (/lib/x86_64-linux-gnu/libc-2.19.so+0x21ec4)
#4 0x400748 (/tmp/a+0x400748)
Address 0x7ffd1d8c0313 is located at offset 163 in frame <e> of T0's stack:
This frame has 3 object(s):
[32, 35) 'data2'
[96, 100) 'data1'
[160, 165) 'buffer'
HINT: this may be a false positive if your program uses some custom stack unwind mechanism or swapcontext
(longjmp and C++ exceptions *are* supported)
Shadow bytes around the buggy address:
0x100023b10010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x100023b10020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x100023b10030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x100023b10040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1
0x100023b10050: f1 f1 03 f4 f4 f4 f2 f2 f2 f2 04 f4 f4 f4 f2 f2
=>0x100023b10060: f2 f2[05]f4 f4 f4 00 00 00 00 00 00 00 00 00 00
0x100023b10070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x100023b10080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x100023b10090: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x100023b100a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x100023b100b0: 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
Heap righ redzone: fb
Freed Heap region: fd
Stack left redzone: f1
Stack mid redzone: f2
Stack right redzone: f3
Stack partial redzone: f4
Stack after return: f5
Stack use after scope: f8
Global redzone: f9
Global init order: f6
Poisoned by user: f7
ASan internal: fe
==21537== ABORTING