ctfwiki--arena 男娘i 2022-01-14 15:05 5885阅读 0赞 参考链接：[https://ctf-wiki.github.io/ctf-wiki/pwn/linux/glibc-heap/heap\_structure-zh/][https_ctf-wiki.github.io_ctf-wiki_pwn_linux_glibc-heap_heap_structure-zh] ## arena ## 无论是主线程还是新创建的线程，在第一次申请内存时，都会有独立的arena。 对于不同的系统，arena 的数量如下： For 32 bit systems: Number of arena = 2 * number of cores. For 64 bit systems: Number of arena = 8 * number of cores. 显然并不是每一个线程都会有对应的 arena。当线程数大于核数的2倍时，必然有线程处于等待状态，因此没有必要为每个线程分配一个arena。 与 thread 不同的是，main\_arena 并不是在申请的 heap 中，而是一个全局变量，在 libc.so的数据段。 ## **heap\_info** ## heap\_info 用来记录申请内存时产生的信息。程序刚开始执行时，每个线程是没有heap区域的。（嗯嗯好像是的，malloc之后才有）此外，一般申请的 heap 是不连续的，因此需要记录不同的 heap 之间的链接结构。 该数据结构是专门为从memory mapping segment 处申请的内存准备的，即为非主线程准备的。 主线程可以通过 sbrk() 拓展 program break location 获得（直接触及mms）。 heap\_info 的主要结构如下： #define HEAP_MIN_SIZE (32 * 1024) #ifndef HEAP_MAX_SIZE # ifdef DEFAULT_MMAP_THRESHOLD_MAX # define HEAP_MAX_SIZE (2 * DEFAULT_MMAP_THRESHOLD_MAX) # else # define HEAP_MAX_SIZE (1024 * 1024) /* must be a power of two */ # endif #endif /* HEAP_MIN_SIZE and HEAP_MAX_SIZE limit the size of mmap()ed heaps that are dynamically created for multi-threaded programs. The maximum size must be a power of two, for fast determination of which heap belongs to a chunk. It should be much larger than the mmap threshold, so that requests with a size just below that threshold can be fulfilled without creating too many heaps. */ /***************************************************************************/ /* A heap is a single contiguous memory region holding (coalesceable) malloc_chunks. It is allocated with mmap() and always starts at an address aligned to HEAP_MAX_SIZE. */ typedef struct _heap_info { mstate ar_ptr; /* Arena for this heap. */ struct _heap_info *prev; /* Previous heap. */ size_t size; /* Current size in bytes. */ size_t mprotect_size; /* Size in bytes that has been mprotected PROT_READ|PROT_WRITE. */ /* Make sure the following data is properly aligned, particularly that sizeof (heap_info) + 2 * SIZE_SZ is a multiple of MALLOC_ALIGNMENT. */ char pad[-6 * SIZE_SZ & MALLOC_ALIGN_MASK]; } heap_info; 该结构主要是描述堆的基本信息，包括 （1）堆对应的 arena 的地址 （2）一个线程可能有多个堆（这不是很正常？），prev 记录了上一个 heap\_info 的地址。单链表链接 heap\_info （3）size 表示当前堆的大小 （4）最后一部分确保对齐（我也不懂啊？？） ## **malloc\_state** ## 该结构用于管理堆。记录每个 arena 当前申请内存的具体状态，如是否有空闲 chunk，有什么大小的空闲 chunk 等等。无论是 thread arena 还是 main arena，它们都只有一个 malloc\_state结构。 由于 thread 的 arena 可能有多个，malloc\_state 结构会在最新申请的 arena中。 main arena 的 malloc\_state 并不是 heap segment 的一部分，而是一个全局变量，存储在 libc.so的数据段。 结构如下： struct malloc_state { /* Serialize access. */ __libc_lock_define(, mutex); /* Flags (formerly in max_fast). */ int flags; /* Fastbins */ mfastbinptr fastbinsY[ NFASTBINS ]; /* Base of the topmost chunk -- not otherwise kept in a bin */ mchunkptr top; /* The remainder from the most recent split of a small request */ mchunkptr last_remainder; /* Normal bins packed as described above */ mchunkptr bins[ NBINS * 2 - 2 ]; /* Bitmap of bins, help to speed up the process of determinating if a given bin is definitely empty.*/ unsigned int binmap[ BINMAPSIZE ]; /* Linked list, points to the next arena */ struct malloc_state *next; /* Linked list for free arenas. Access to this field is serialized by free_list_lock in arena.c. */ struct malloc_state *next_free; /* Number of threads attached to this arena. 0 if the arena is on the free list. Access to this field is serialized by free_list_lock in arena.c. */ INTERNAL_SIZE_T attached_threads; /* Memory allocated from the system in this arena. */ INTERNAL_SIZE_T system_mem; INTERNAL_SIZE_T max_system_mem; }; （1）\_libc\_lock\_define(,mutex): 该变量用于控制程序串行访问同一个分配区，当一个线程获取了分配区后，其他线程要想访问该分配区，就必须等待该线程分配完成后才能使用。 （2）flags: 记录了一些分配区的标志，比如bit0记录了分配区是否有fast bin chunk，bit1 标识分配区是否能返回连续的虚拟地址空间。具体如下： /* FASTCHUNKS_BIT held in max_fast indicates that there are probably some fastbin chunks. It is set true on entering a chunk into any fastbin, and cleared only in malloc_consolidate. The truth value is inverted so that have_fastchunks will be true upon startup (since statics are zero-filled), simplifying initialization checks. */ #define FASTCHUNKS_BIT (1U) #define have_fastchunks(M) (((M)->flags & FASTCHUNKS_BIT) == 0) #define clear_fastchunks(M) catomic_or(&(M)->flags, FASTCHUNKS_BIT) #define set_fastchunks(M) catomic_and(&(M)->flags, ~FASTCHUNKS_BIT) /* NONCONTIGUOUS_BIT indicates that MORECORE does not return contiguous regions. Otherwise, contiguity is exploited in merging together, when possible, results from consecutive MORECORE calls. The initial value comes from MORECORE_CONTIGUOUS, but is changed dynamically if mmap is ever used as an sbrk substitute. */ #define NONCONTIGUOUS_BIT (2U) #define contiguous(M) (((M)->flags & NONCONTIGUOUS_BIT) == 0) #define noncontiguous(M) (((M)->flags & NONCONTIGUOUS_BIT) != 0) #define set_noncontiguous(M) ((M)->flags |= NONCONTIGUOUS_BIT) #define set_contiguous(M) ((M)->flags &= ~NONCONTIGUOUS_BIT) /* ARENA_CORRUPTION_BIT is set if a memory corruption was detected on the arena. Such an arena is no longer used to allocate chunks. Chunks allocated in that arena before detecting corruption are not freed. */ #define ARENA_CORRUPTION_BIT (4U) #define arena_is_corrupt(A) (((A)->flags & ARENA_CORRUPTION_BIT)) #define set_arena_corrupt(A) ((A)->flags |= ARENA_CORRUPTION_BIT) （3）fastbinsY\[NFASTBINS\] 存放每个 fast chunk 链表头部的指针 （4）top 指向分配区的 top chunk （5）last\_reminder 最新的 chunk 分割之后剩下的那部分 （6）bins 用于存储 unstored bin, small bins, large bins 的 chunk 链表 （7）binmap ptmalloc 用一个 bit 来标识某一个 bin 中是否包含空闲的 chunk. [https_ctf-wiki.github.io_ctf-wiki_pwn_linux_glibc-heap_heap_structure-zh]: https://ctf-wiki.github.io/ctf-wiki/pwn/linux/glibc-heap/heap_structure-zh/
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