binder: fix UAF caused by offsets overwrite

In the Linux kernel, the following vulnerability has been resolved:

binder: fix UAF caused by offsets overwrite

Binder objects are processed and copied individually into the target

buffer during transactions. Any raw data in-between these objects is

copied as well. However, this raw data copy lacks an out-of-bounds

check. If the raw data exceeds the data section size then the copy

overwrites the offsets section. This eventually triggers an error that

attempts to unwind the processed objects. However, at this point the

offsets used to index these objects are now corrupted.

Unwinding with corrupted offsets can result in decrements of arbitrary

nodes and lead to their premature release. Other users of such nodes are

left with a dangling pointer triggering a use-after-free. This issue is

made evident by the following KASAN report (trimmed):

==================================================================

BUG: KASAN: slab-use-after-free in _raw_spin_lock+0xe4/0x19c

Write of size 4 at addr ffff47fc91598f04 by task binder-util/743

CPU: 9 UID: 0 PID: 743 Comm: binder-util Not tainted 6.11.0-rc4 #1

Hardware name: linux,dummy-virt (DT)

Call trace:

_raw_spin_lock+0xe4/0x19c

binder_free_buf+0x128/0x434

binder_thread_write+0x8a4/0x3260

binder_ioctl+0x18f0/0x258c

[...]

Allocated by task 743:

__kmalloc_cache_noprof+0x110/0x270

binder_new_node+0x50/0x700

binder_transaction+0x413c/0x6da8

binder_thread_write+0x978/0x3260

binder_ioctl+0x18f0/0x258c

[...]

Freed by task 745:

kfree+0xbc/0x208

binder_thread_read+0x1c5c/0x37d4

binder_ioctl+0x16d8/0x258c

[...]

==================================================================

To avoid this issue, let's check that the raw data copy is within the

boundaries of the data section.