From: Carlos Llamas Date: Fri, 19 Jun 2026 18:52:31 +0000 (+0000) Subject: binder: fix UAF in binder_free_transaction() X-Git-Tag: v7.2-rc3~3^2~4 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f223d27a546c1e1f48d38fd67760e78f068fe8c4;p=thirdparty%2Fkernel%2Flinux.git 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. Cc: stable Reported-by: Alice Ryhl Closes: https://lore.kernel.org/all/aikJKVuny_eOivwN@google.com/ Fixes: a370003cc301 ("binder: fix possible UAF when freeing buffer") Signed-off-by: Carlos Llamas Reviewed-by: Alice Ryhl Link: https://patch.msgid.link/20260619185233.2194678-2-cmllamas@google.com Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 013e2bfab070..8f2ef1bd539f 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -1658,10 +1658,19 @@ static void binder_txn_latency_free(struct binder_transaction *t) static void binder_free_transaction(struct binder_transaction *t) { + struct binder_thread *target_thread; struct binder_proc *target_proc; spin_lock(&t->lock); target_proc = t->to_proc; + target_thread = t->to_thread; + /* + * Pin target_thread to keep target_proc alive. Undelivered + * transactions with !target_thread are safe, as target_proc + * can only be the current context there. + */ + if (target_thread) + atomic_inc(&target_thread->tmp_ref); spin_unlock(&t->lock); if (target_proc) { @@ -1676,6 +1685,10 @@ static void binder_free_transaction(struct binder_transaction *t) t->buffer->transaction = NULL; binder_inner_proc_unlock(target_proc); } + + if (target_thread) + binder_thread_dec_tmpref(target_thread); + if (trace_binder_txn_latency_free_enabled()) binder_txn_latency_free(t); /*