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@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx>
---
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,
--
2.46.0.295.g3b9ea8a38a-goog
