binder: fix UAF in binder_netlink_report()

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

binder: fix UAF in binder_netlink_report()

Oneway transactions sent to frozen targets via binder_proc_transaction()

return a BR_TRANSACTION_PENDING_FROZEN error but they are still treated

as successful since the target is expected to thaw at some point. It is

then not safe to access 't' after BR_TRANSACTION_PENDING_FROZEN errors

as the transaction could have been consumed by the now thawed target.

This is the case for binder_netlink_report() which derreferences 't'

after a pending frozen error, as pointed out by the following KASAN

report:

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

BUG: KASAN: slab-use-after-free in binder_netlink_report.isra.0+0x694/0x6c8

Read of size 8 at addr ffff00000f98ba38 by task binder-util/522

CPU: 4 UID: 0 PID: 522 Comm: binder-util Not tainted 6.19.0-rc6-00015-gc03e9c42ae8f #1 PREEMPT

Hardware name: linux,dummy-virt (DT)

Call trace:

binder_netlink_report.isra.0+0x694/0x6c8

binder_transaction+0x66e4/0x79b8

binder_thread_write+0xab4/0x4440

binder_ioctl+0x1fd4/0x2940

[...]

Allocated by task 522:

__kmalloc_cache_noprof+0x17c/0x50c

binder_transaction+0x584/0x79b8

binder_thread_write+0xab4/0x4440

binder_ioctl+0x1fd4/0x2940

[...]

Freed by task 488:

kfree+0x1d0/0x420

binder_free_transaction+0x150/0x234

binder_thread_read+0x2d08/0x3ce4

binder_ioctl+0x488/0x2940

[...]

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

Instead, make a transaction copy so the data can be safely accessed by

binder_netlink_report() after a pending frozen error. While here, add a

comment about not using t->buffer in binder_netlink_report().