Changing write direction on Stack · general

Stream: general

Topic: Changing write direction on Stack

Lasse (Jul 09 2024 at 11:39):

I tried to reproduce the example in Fig. 5 https://www.usenix.org/system/files/sec20-lehmann.pdf
It seems like the write direction is the same as the grow direction of the Stack.

Is there a possibility to change the writing direction?

Compiled with clang (llvm 18):

/usr/lib/llvm-18/bin/clang --sysroot /tmp/wasi-libc -Wl,--no-entry -Wl,--export-all -Wall -Wextra -O3 -Wl,--stack-first --target=wasm32-unknown-wasi -o buffer_overflow.wasm buffer_overflow.c

Code excerpt:

void vulnerable() {
    const char same_frame[8] = "BBBBBBBB";
    char buffer[8];

    scanf("%[^\n]", buffer);

    printf("\n\nbuffer: %s\n", buffer);
    printf("same_frame: %s\n", same_frame);
}

void parent() {
    char parent_frame[8] = "AAAAAAAA";
    vulnerable();
    printf("parent_frame: %s\n", parent_frame);

    for (size_t* i = (size_t*) parent_frame-40; i < (size_t*) (parent_frame+40); i++) // (parent_frame-40)
        printf("%p %08zx \n", i, *i);
}

when entering 12xC. It overwrites the same_frame buffer.

buffer: CCCCCCCCCCCC
same_frame: CCCC
parent_frame: AAAAAAAACCCCCCCCCCCC

Stack:
0xffd4 00000000
0xffd8 41414141
0xffdc 41414141
0xffe0 43434343
0xffe4 43434343
0xffe8 43434343
0xffec 42424200
0xfff0 00000000
0xfff4 00000000

Last updated: Dec 23 2024 at 12:05 UTC