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().

Affected Software

References

• https://git.kernel.org/stable/c/5e8a3d01544282e50d887d76f30d1496a0a53562
• https://git.kernel.org/stable/c/a6050dedb6f1cc23e518e3a132ab74a0aad6df90