From c7498034bec481a3571f4484c7c6e300374c87fe Mon Sep 17 00:00:00 2001 From: Todd Kjos Date: Tue, 6 Nov 2018 15:55:32 -0800 Subject: [PATCH] UPSTREAM: binder: fix race that allows malicious free of live buffer MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit commit 7bada55ab50697861eee6bb7d60b41e68a961a9c upstream Malicious code can attempt to free buffers using the BC_FREE_BUFFER ioctl to binder. There are protections against a user freeing a buffer while in use by the kernel, however there was a window where BC_FREE_BUFFER could be used to free a recently allocated buffer that was not completely initialized. This resulted in a use-after-free detected by KASAN with a malicious test program. This window is closed by setting the buffer's allow_user_free attribute to 0 when the buffer is allocated or when the user has previously freed it instead of waiting for the caller to set it. The problem was that when the struct buffer was recycled, allow_user_free was stale and set to 1 allowing a free to go through. Bug: 116855682 Change-Id: I0b38089f6fdb1adbf7e1102747e4119c9a05b191 Signed-off-by: Todd Kjos Acked-by: Arve Hjønnevåg Cc: stable # 4.14 Signed-off-by: Greg Kroah-Hartman (cherry picked from commit c3d21ec4d4fb68baf47248dfe0e0ce0080fd7bcc) --- drivers/android/binder.c | 21 ++++++++++++--------- drivers/android/binder_alloc.c | 14 ++++++-------- drivers/android/binder_alloc.h | 3 +-- 3 files changed, 19 insertions(+), 19 deletions(-) diff --git a/drivers/android/binder.c b/drivers/android/binder.c index 3007b28206d7..6f7155b8d198 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -3138,7 +3138,6 @@ static void binder_transaction(struct binder_proc *proc, t->buffer = NULL; goto err_binder_alloc_buf_failed; } - t->buffer->allow_user_free = 0; t->buffer->debug_id = t->debug_id; t->buffer->transaction = t; t->buffer->target_node = target_node; @@ -3634,14 +3633,18 @@ static int binder_thread_write(struct binder_proc *proc, buffer = binder_alloc_prepare_to_free(&proc->alloc, data_ptr); - if (buffer == NULL) { - binder_user_error("%d:%d BC_FREE_BUFFER u%016llx no match\n", - proc->pid, thread->pid, (u64)data_ptr); - break; - } - if (!buffer->allow_user_free) { - binder_user_error("%d:%d BC_FREE_BUFFER u%016llx matched unreturned buffer\n", - proc->pid, thread->pid, (u64)data_ptr); + if (IS_ERR_OR_NULL(buffer)) { + if (PTR_ERR(buffer) == -EPERM) { + binder_user_error( + "%d:%d BC_FREE_BUFFER u%016llx matched unreturned or currently freeing buffer\n", + proc->pid, thread->pid, + (u64)data_ptr); + } else { + binder_user_error( + "%d:%d BC_FREE_BUFFER u%016llx no match\n", + proc->pid, thread->pid, + (u64)data_ptr); + } break; } binder_debug(BINDER_DEBUG_FREE_BUFFER, diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c index 1d9db2ef26bd..baecb4bf9d9b 100644 --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -149,14 +149,12 @@ static struct binder_buffer *binder_alloc_prepare_to_free_locked( else { /* * Guard against user threads attempting to - * free the buffer twice + * free the buffer when in use by kernel or + * after it's already been freed. */ - if (buffer->free_in_progress) { - pr_err("%d:%d FREE_BUFFER u%016llx user freed buffer twice\n", - alloc->pid, current->pid, (u64)user_ptr); - return NULL; - } - buffer->free_in_progress = 1; + if (!buffer->allow_user_free) + return ERR_PTR(-EPERM); + buffer->allow_user_free = 0; return buffer; } } @@ -463,7 +461,7 @@ static struct binder_buffer *binder_alloc_new_buf_locked( rb_erase(best_fit, &alloc->free_buffers); buffer->free = 0; - buffer->free_in_progress = 0; + buffer->allow_user_free = 0; binder_insert_allocated_buffer_locked(alloc, buffer); binder_alloc_debug(BINDER_DEBUG_BUFFER_ALLOC, "%d: binder_alloc_buf size %zd got %pK\n", diff --git a/drivers/android/binder_alloc.h b/drivers/android/binder_alloc.h index 9ef64e563856..fb3238c74c8a 100644 --- a/drivers/android/binder_alloc.h +++ b/drivers/android/binder_alloc.h @@ -50,8 +50,7 @@ struct binder_buffer { unsigned free:1; unsigned allow_user_free:1; unsigned async_transaction:1; - unsigned free_in_progress:1; - unsigned debug_id:28; + unsigned debug_id:29; struct binder_transaction *transaction;