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![Todd Kjos](/assets/img/avatar_default.png)
Malicious code can attempt to free buffers using the BC_FREE_BUFFER ioctl to binder. There are protections against a user freeing a buffer while in use by the kernel, however there was a window where BC_FREE_BUFFER could be used to free a recently allocated buffer that was not completely initialized. This resulted in a use-after-free detected by KASAN with a malicious test program. This window is closed by setting the buffer's allow_user_free attribute to 0 when the buffer is allocated or when the user has previously freed it instead of waiting for the caller to set it. The problem was that when the struct buffer was recycled, allow_user_free was stale and set to 1 allowing a free to go through. Signed-off-by: Todd Kjos <tkjos@google.com> Acked-by: Arve Hjønnevåg <arve@android.com> Cc: stable <stable@vger.kernel.org> # 4.14 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
187 lines
6.6 KiB
C
187 lines
6.6 KiB
C
/*
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* Copyright (C) 2017 Google, Inc.
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*
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* This software is licensed under the terms of the GNU General Public
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* License version 2, as published by the Free Software Foundation, and
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* may be copied, distributed, and modified under those terms.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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*/
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#ifndef _LINUX_BINDER_ALLOC_H
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#define _LINUX_BINDER_ALLOC_H
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#include <linux/rbtree.h>
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#include <linux/list.h>
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#include <linux/mm.h>
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#include <linux/rtmutex.h>
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#include <linux/vmalloc.h>
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#include <linux/slab.h>
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#include <linux/list_lru.h>
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extern struct list_lru binder_alloc_lru;
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struct binder_transaction;
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/**
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* struct binder_buffer - buffer used for binder transactions
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* @entry: entry alloc->buffers
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* @rb_node: node for allocated_buffers/free_buffers rb trees
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* @free: true if buffer is free
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* @allow_user_free: describe the second member of struct blah,
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* @async_transaction: describe the second member of struct blah,
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* @debug_id: describe the second member of struct blah,
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* @transaction: describe the second member of struct blah,
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* @target_node: describe the second member of struct blah,
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* @data_size: describe the second member of struct blah,
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* @offsets_size: describe the second member of struct blah,
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* @extra_buffers_size: describe the second member of struct blah,
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* @data:i describe the second member of struct blah,
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*
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* Bookkeeping structure for binder transaction buffers
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*/
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struct binder_buffer {
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struct list_head entry; /* free and allocated entries by address */
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struct rb_node rb_node; /* free entry by size or allocated entry */
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/* by address */
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unsigned free:1;
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unsigned allow_user_free:1;
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unsigned async_transaction:1;
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unsigned debug_id:29;
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struct binder_transaction *transaction;
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struct binder_node *target_node;
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size_t data_size;
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size_t offsets_size;
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size_t extra_buffers_size;
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void *data;
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};
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/**
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* struct binder_lru_page - page object used for binder shrinker
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* @page_ptr: pointer to physical page in mmap'd space
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* @lru: entry in binder_alloc_lru
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* @alloc: binder_alloc for a proc
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*/
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struct binder_lru_page {
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struct list_head lru;
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struct page *page_ptr;
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struct binder_alloc *alloc;
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};
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/**
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* struct binder_alloc - per-binder proc state for binder allocator
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* @vma: vm_area_struct passed to mmap_handler
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* (invarient after mmap)
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* @tsk: tid for task that called init for this proc
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* (invariant after init)
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* @vma_vm_mm: copy of vma->vm_mm (invarient after mmap)
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* @buffer: base of per-proc address space mapped via mmap
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* @user_buffer_offset: offset between user and kernel VAs for buffer
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* @buffers: list of all buffers for this proc
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* @free_buffers: rb tree of buffers available for allocation
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* sorted by size
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* @allocated_buffers: rb tree of allocated buffers sorted by address
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* @free_async_space: VA space available for async buffers. This is
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* initialized at mmap time to 1/2 the full VA space
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* @pages: array of binder_lru_page
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* @buffer_size: size of address space specified via mmap
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* @pid: pid for associated binder_proc (invariant after init)
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* @pages_high: high watermark of offset in @pages
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*
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* Bookkeeping structure for per-proc address space management for binder
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* buffers. It is normally initialized during binder_init() and binder_mmap()
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* calls. The address space is used for both user-visible buffers and for
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* struct binder_buffer objects used to track the user buffers
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*/
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struct binder_alloc {
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struct mutex mutex;
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struct vm_area_struct *vma;
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struct mm_struct *vma_vm_mm;
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void *buffer;
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ptrdiff_t user_buffer_offset;
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struct list_head buffers;
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struct rb_root free_buffers;
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struct rb_root allocated_buffers;
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size_t free_async_space;
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struct binder_lru_page *pages;
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size_t buffer_size;
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uint32_t buffer_free;
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int pid;
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size_t pages_high;
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};
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#ifdef CONFIG_ANDROID_BINDER_IPC_SELFTEST
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void binder_selftest_alloc(struct binder_alloc *alloc);
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#else
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static inline void binder_selftest_alloc(struct binder_alloc *alloc) {}
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#endif
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enum lru_status binder_alloc_free_page(struct list_head *item,
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struct list_lru_one *lru,
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spinlock_t *lock, void *cb_arg);
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extern struct binder_buffer *binder_alloc_new_buf(struct binder_alloc *alloc,
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size_t data_size,
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size_t offsets_size,
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size_t extra_buffers_size,
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int is_async);
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extern void binder_alloc_init(struct binder_alloc *alloc);
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extern int binder_alloc_shrinker_init(void);
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extern void binder_alloc_vma_close(struct binder_alloc *alloc);
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extern struct binder_buffer *
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binder_alloc_prepare_to_free(struct binder_alloc *alloc,
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uintptr_t user_ptr);
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extern void binder_alloc_free_buf(struct binder_alloc *alloc,
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struct binder_buffer *buffer);
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extern int binder_alloc_mmap_handler(struct binder_alloc *alloc,
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struct vm_area_struct *vma);
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extern void binder_alloc_deferred_release(struct binder_alloc *alloc);
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extern int binder_alloc_get_allocated_count(struct binder_alloc *alloc);
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extern void binder_alloc_print_allocated(struct seq_file *m,
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struct binder_alloc *alloc);
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void binder_alloc_print_pages(struct seq_file *m,
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struct binder_alloc *alloc);
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/**
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* binder_alloc_get_free_async_space() - get free space available for async
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* @alloc: binder_alloc for this proc
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*
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* Return: the bytes remaining in the address-space for async transactions
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*/
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static inline size_t
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binder_alloc_get_free_async_space(struct binder_alloc *alloc)
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{
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size_t free_async_space;
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mutex_lock(&alloc->mutex);
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free_async_space = alloc->free_async_space;
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mutex_unlock(&alloc->mutex);
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return free_async_space;
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}
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/**
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* binder_alloc_get_user_buffer_offset() - get offset between kernel/user addrs
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* @alloc: binder_alloc for this proc
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*
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* Return: the offset between kernel and user-space addresses to use for
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* virtual address conversion
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*/
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static inline ptrdiff_t
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binder_alloc_get_user_buffer_offset(struct binder_alloc *alloc)
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{
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/*
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* user_buffer_offset is constant if vma is set and
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* undefined if vma is not set. It is possible to
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* get here with !alloc->vma if the target process
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* is dying while a transaction is being initiated.
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* Returning the old value is ok in this case and
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* the transaction will fail.
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*/
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return alloc->user_buffer_offset;
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}
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#endif /* _LINUX_BINDER_ALLOC_H */
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