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

binder: fix UAF in binder_free_transaction()

In binder_free_transaction(), the t->to_proc is read under the t->lock. However, once the t->lock is dropped, the to_proc can die in parallel. This leads to a use-after-free error when we attempt to acquire its inner lock right afterwards:

================================================================== BUG: KASAN: slab-use-after-free in _raw_spin_lock+0xe4/0x1a0 Write of size 4 at addr ffff00001125da70 by task B/672

CPU: 20 UID: 0 PID: 672 Comm: B Not tainted 7.1.0-rc6-00284-g8e65320d91cd #4 PREEMPT Hardware name: linux,dummy-virt (DT) Call trace: _raw_spin_lock+0xe4/0x1a0 binder_free_transaction+0x8c/0x320 binder_send_failed_reply+0x21c/0x2f8 binder_thread_release+0x488/0x7e0 binder_ioctl+0x12c0/0x29a0 […]

Allocated by task 675: __kmalloc_cache_noprof+0x174/0x444 binder_open+0x118/0xb70 do_dentry_open+0x374/0x1040 vfs_open+0x58/0x3bc […]

Freed by task 212: __kasan_slab_free+0x58/0x80 kfree+0x1a0/0x4a4 binder_proc_dec_tmpref+0x32c/0x5e0 binder_deferred_func+0xc48/0x104c process_one_work+0x53c/0xbc0 […]

To prevent this, pin the target thread (t->to_thread) to guarantee the target process remains alive. Undelivered transactions without a target thread are already safe, as the target process can only be the current context in those paths.

Affected Software

References

• https://git.kernel.org/stable/c/0be901ab1dcc4af59b88f2e324493bb283850167
• https://git.kernel.org/stable/c/0f15f0f6ca5df566275ce517f257af2559528b41
• https://git.kernel.org/stable/c/328ccf32acb87e8bbb1fe2b065068c574e4db2bf
• https://git.kernel.org/stable/c/45df558c543bb5543bacc8065fd7c567740781e5
• https://git.kernel.org/stable/c/48aeda9f8039e4a6971d1804578efde7f2c01eda
• https://git.kernel.org/stable/c/5602a43f251c3d75312df91a422675fc00ca3dce
• https://git.kernel.org/stable/c/d45ef513eed1abebfec90c3cfb6ae50c2a4182db
• https://git.kernel.org/stable/c/f223d27a546c1e1f48d38fd67760e78f068fe8c4