CVE-2024-56555 — binder: fix OOB in binder_add_freeze_work()

Affected: Linux

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

binder: fix OOB in binder_add_freeze_work()

In binder_add_freeze_work() we iterate over the proc->nodes with the proc->inner_lock held. However, this lock is temporarily dropped to acquire the node->lock first (lock nesting order). This can race with binder_deferred_release() which removes the nodes from the proc->nodes rbtree and adds them into binder_dead_nodes list. This leads to a broken iteration in binder_add_freeze_work() as rb_next() will use data from binder_dead_nodes, triggering an out-of-bounds access:

================================================================== BUG: KASAN: global-out-of-bounds in rb_next+0xfc/0x124 Read of size 8 at addr ffffcb84285f7170 by task freeze/660

CPU: 8 UID: 0 PID: 660 Comm: freeze Not tainted 6.11.0-07343-ga727812a8d45 #18 Hardware name: linux,dummy-virt (DT) Call trace: rb_next+0xfc/0x124 binder_add_freeze_work+0x344/0x534 binder_ioctl+0x1e70/0x25ac __arm64_sys_ioctl+0x124/0x190

The buggy address belongs to the variable: binder_dead_nodes+0x10/0x40 [...] ==================================================================

This is possible because proc->nodes (rbtree) and binder_dead_nodes (list) share entries in binder_node through a union:

struct binder_node { [...] union { struct rb_node rb_node; struct hlist_node dead_node; };

Fix the race by checking that the proc is still alive. If not, simply break out of…

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CVE-2024-56555 — binder: fix OOB in binder_add_freeze_work()