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binder: protect against two threads freeing buffer

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Adds protection against malicious user code freeing
the same buffer at the same time which could cause
a crash. Cannot happen under normal use.

Bug: 36650912
Change-Id: I43e078cbf31c0789aaff5ceaf8f1a94c75f79d45
Test: tested manually
Signed-off-by: Todd Kjos <tkjos@google.com>
This commit is contained in:
Todd Kjos
2017-04-21 14:32:11 -07:00
parent 4ea3c9accb
commit eda5c2c85d
3 changed files with 20 additions and 7 deletions
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4
drivers/android/binder.c
View File

@@ -2613,8 +2613,8 @@ static int binder_thread_write(struct binder_proc *proc,
return -EFAULT;
ptr += sizeof(binder_uintptr_t);
buffer = binder_alloc_buffer_lookup(&proc->alloc,
data_ptr);
buffer = binder_alloc_prepare_to_free(&proc->alloc,
data_ptr);
if (buffer == NULL) {
binder_user_error("%d:%d BC_FREE_BUFFER u%016llx no match\n",
proc->pid, thread->pid, (u64)data_ptr);

16
drivers/android/binder_alloc.c
View File

@@ -113,8 +113,8 @@ static void binder_insert_allocated_buffer(struct binder_alloc *alloc,
rb_insert_color(&new_buffer->rb_node, &alloc->allocated_buffers);
}
struct binder_buffer *binder_alloc_buffer_lookup(struct binder_alloc *alloc,
uintptr_t user_ptr)
struct binder_buffer *binder_alloc_prepare_to_free(struct binder_alloc *alloc,
uintptr_t user_ptr)
{
struct rb_node *n;
struct binder_buffer *buffer;
@@ -134,6 +134,17 @@ struct binder_buffer *binder_alloc_buffer_lookup(struct binder_alloc *alloc,
else if (kern_ptr > buffer)
n = n->rb_right;
else {
/*
* Guard against user threads attempting to
* free the buffer twice
*/
if (!buffer->free_in_progress) {
buffer->free_in_progress = 1;
} else {
pr_err("%d:%d FREE_BUFFER u%016llx user freed buffer twice\n",
alloc->pid, current->pid, (u64)user_ptr);
buffer = NULL;
}
mutex_unlock(&alloc->mutex);
return buffer;
}
@@ -375,6 +386,7 @@ struct binder_buffer *binder_alloc_new_buf(struct binder_alloc *alloc,
rb_erase(best_fit, &alloc->free_buffers);
buffer->free = 0;
buffer->free_in_progress = 0;
binder_insert_allocated_buffer(alloc, buffer);
if (buffer_size != size) {
struct binder_buffer *new_buffer = (void *)buffer->data + size;

7
drivers/android/binder_alloc.h
View File

@@ -36,7 +36,8 @@ struct binder_buffer {
unsigned free:1;
unsigned allow_user_free:1;
unsigned async_transaction:1;
unsigned debug_id:29;
unsigned free_in_progress:1;
unsigned debug_id:28;
struct binder_transaction *transaction;
@@ -72,8 +73,8 @@ extern struct binder_buffer *binder_alloc_new_buf(struct binder_alloc *alloc,
extern void binder_alloc_init(struct binder_alloc *alloc);
extern void binder_alloc_vma_close(struct binder_alloc *alloc);
extern struct binder_buffer *
binder_alloc_buffer_lookup(struct binder_alloc *alloc,
uintptr_t user_ptr);
binder_alloc_prepare_to_free(struct binder_alloc *alloc,
uintptr_t user_ptr);
extern void binder_alloc_free_buf(struct binder_alloc *alloc,
struct binder_buffer *buffer);
extern int binder_alloc_mmap_handler(struct binder_alloc *alloc,