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authorTodd Kjos <tkjos@android.com>2018-11-06 15:55:32 -0800
committerTodd Kjos <tkjos@google.com>2018-12-03 18:33:47 +0000
commit8250e54af25dadfe8de0a86ca0d3a60d9da7b8dc (patch)
tree7e040af13b83e15d9712e18cbc996bf8514e7ccb
parent3a8d064a2c2548c2319b8950e942da81aeccc739 (diff)
UPSTREAM: binder: fix race that allows malicious free of live bufferASB-2018-12-05_4.4-p
commit 7bada55ab50697861eee6bb7d60b41e68a961a9c upstream 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. Bug: 116855682 Change-Id: I0b38089f6fdb1adbf7e1102747e4119c9a05b191 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>
-rw-r--r--drivers/android/binder.c21
-rw-r--r--drivers/android/binder_alloc.c14
-rw-r--r--drivers/android/binder_alloc.h3
3 files changed, 19 insertions, 19 deletions
diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index e0c46ce312d7..9294574c8251 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -3138,7 +3138,6 @@ static void binder_transaction(struct binder_proc *proc,
t->buffer = NULL;
goto err_binder_alloc_buf_failed;
}
- t->buffer->allow_user_free = 0;
t->buffer->debug_id = t->debug_id;
t->buffer->transaction = t;
t->buffer->target_node = target_node;
@@ -3634,14 +3633,18 @@ static int binder_thread_write(struct binder_proc *proc,
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);
- break;
- }
- if (!buffer->allow_user_free) {
- binder_user_error("%d:%d BC_FREE_BUFFER u%016llx matched unreturned buffer\n",
- proc->pid, thread->pid, (u64)data_ptr);
+ if (IS_ERR_OR_NULL(buffer)) {
+ if (PTR_ERR(buffer) == -EPERM) {
+ binder_user_error(
+ "%d:%d BC_FREE_BUFFER u%016llx matched unreturned or currently freeing buffer\n",
+ proc->pid, thread->pid,
+ (u64)data_ptr);
+ } else {
+ binder_user_error(
+ "%d:%d BC_FREE_BUFFER u%016llx no match\n",
+ proc->pid, thread->pid,
+ (u64)data_ptr);
+ }
break;
}
binder_debug(BINDER_DEBUG_FREE_BUFFER,
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 1d9db2ef26bd..baecb4bf9d9b 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -149,14 +149,12 @@ static struct binder_buffer *binder_alloc_prepare_to_free_locked(
else {
/*
* Guard against user threads attempting to
- * free the buffer twice
+ * free the buffer when in use by kernel or
+ * after it's already been freed.
*/
- if (buffer->free_in_progress) {
- pr_err("%d:%d FREE_BUFFER u%016llx user freed buffer twice\n",
- alloc->pid, current->pid, (u64)user_ptr);
- return NULL;
- }
- buffer->free_in_progress = 1;
+ if (!buffer->allow_user_free)
+ return ERR_PTR(-EPERM);
+ buffer->allow_user_free = 0;
return buffer;
}
}
@@ -463,7 +461,7 @@ static struct binder_buffer *binder_alloc_new_buf_locked(
rb_erase(best_fit, &alloc->free_buffers);
buffer->free = 0;
- buffer->free_in_progress = 0;
+ buffer->allow_user_free = 0;
binder_insert_allocated_buffer_locked(alloc, buffer);
binder_alloc_debug(BINDER_DEBUG_BUFFER_ALLOC,
"%d: binder_alloc_buf size %zd got %pK\n",
diff --git a/drivers/android/binder_alloc.h b/drivers/android/binder_alloc.h
index 9ef64e563856..fb3238c74c8a 100644
--- a/drivers/android/binder_alloc.h
+++ b/drivers/android/binder_alloc.h
@@ -50,8 +50,7 @@ struct binder_buffer {
unsigned free:1;
unsigned allow_user_free:1;
unsigned async_transaction:1;
- unsigned free_in_progress:1;
- unsigned debug_id:28;
+ unsigned debug_id:29;
struct binder_transaction *transaction;