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.
Fixes: 6d98eb95b450 ("binder: avoid potential data leakage when copying txn") Cc: Todd Kjos tkjos@google.com Cc: stable@vger.kernel.org Signed-off-by: Carlos Llamas cmllamas@google.com --- drivers/android/binder.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 905290c98c3c..e8643c69d426 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -3422,6 +3422,7 @@ static void binder_transaction(struct binder_proc *proc, */ copy_size = object_offset - user_offset; if (copy_size && (user_offset > object_offset || + object_offset > tr->data_size || binder_alloc_copy_user_to_buffer( &target_proc->alloc, t->buffer, user_offset,