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Date: Fri, 5 May 2023 16:20:18 -0700
From: Todd Kjos <tkjos@...gle.com>
To: Carlos Llamas <cmllamas@...gle.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Arve Hjønnevåg <arve@...roid.com>,
Todd Kjos <tkjos@...roid.com>,
Martijn Coenen <maco@...roid.com>,
Joel Fernandes <joel@...lfernandes.org>,
Christian Brauner <brauner@...nel.org>,
Suren Baghdasaryan <surenb@...gle.com>,
linux-kernel@...r.kernel.org, kernel-team@...roid.com,
Zi Fan Tan <zifantan@...gle.com>, stable@...r.kernel.org
Subject: Re: [PATCH v2] binder: fix UAF caused by faulty buffer cleanup
On Fri, May 5, 2023 at 1:30 PM Carlos Llamas <cmllamas@...gle.com> wrote:
>
> In binder_transaction_buffer_release() the 'failed_at' offset indicates
> the number of objects to clean up. However, this function was changed by
> commit 44d8047f1d87 ("binder: use standard functions to allocate fds"),
> to release all the objects in the buffer when 'failed_at' is zero.
>
> This introduced an issue when a transaction buffer is released without
> any objects having been processed so far. In this case, 'failed_at' is
> indeed zero yet it is misinterpreted as releasing the entire buffer.
>
> This leads to use-after-free errors where nodes are incorrectly freed
> and subsequently accessed. Such is the case in the following KASAN
> report:
>
> ==================================================================
> BUG: KASAN: slab-use-after-free in binder_thread_read+0xc40/0x1f30
> Read of size 8 at addr ffff4faf037cfc58 by task poc/474
>
> CPU: 6 PID: 474 Comm: poc Not tainted 6.3.0-12570-g7df047b3f0aa #5
> Hardware name: linux,dummy-virt (DT)
> Call trace:
> dump_backtrace+0x94/0xec
> show_stack+0x18/0x24
> dump_stack_lvl+0x48/0x60
> print_report+0xf8/0x5b8
> kasan_report+0xb8/0xfc
> __asan_load8+0x9c/0xb8
> binder_thread_read+0xc40/0x1f30
> binder_ioctl+0xd9c/0x1768
> __arm64_sys_ioctl+0xd4/0x118
> invoke_syscall+0x60/0x188
> [...]
>
> Allocated by task 474:
> kasan_save_stack+0x3c/0x64
> kasan_set_track+0x2c/0x40
> kasan_save_alloc_info+0x24/0x34
> __kasan_kmalloc+0xb8/0xbc
> kmalloc_trace+0x48/0x5c
> binder_new_node+0x3c/0x3a4
> binder_transaction+0x2b58/0x36f0
> binder_thread_write+0x8e0/0x1b78
> binder_ioctl+0x14a0/0x1768
> __arm64_sys_ioctl+0xd4/0x118
> invoke_syscall+0x60/0x188
> [...]
>
> Freed by task 475:
> kasan_save_stack+0x3c/0x64
> kasan_set_track+0x2c/0x40
> kasan_save_free_info+0x38/0x5c
> __kasan_slab_free+0xe8/0x154
> __kmem_cache_free+0x128/0x2bc
> kfree+0x58/0x70
> binder_dec_node_tmpref+0x178/0x1fc
> binder_transaction_buffer_release+0x430/0x628
> binder_transaction+0x1954/0x36f0
> binder_thread_write+0x8e0/0x1b78
> binder_ioctl+0x14a0/0x1768
> __arm64_sys_ioctl+0xd4/0x118
> invoke_syscall+0x60/0x188
> [...]
> ==================================================================
>
> In order to avoid these issues, let's always calculate the intended
> 'failed_at' offset beforehand. This is renamed and wrapped in a helper
> function to make it clear and convenient.
>
> Fixes: 32e9f56a96d8 ("binder: don't detect sender/target during buffer cleanup")
> Reported-by: Zi Fan Tan <zifantan@...gle.com>
> Cc: stable@...r.kernel.org
> Signed-off-by: Carlos Llamas <cmllamas@...gle.com>
Acked-by: Todd Kjos <tkjos@...gle.com>
> ---
> v2: rename 'failed_at' to 'off_end_offsets' and drop the now unecessary
> comments after the rename per Todd's feedback.
>
> drivers/android/binder.c | 28 +++++++++++++++++++++-------
> 1 file changed, 21 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index fb56bfc45096..8fb7672021ee 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -1934,24 +1934,23 @@ static void binder_deferred_fd_close(int fd)
> static void binder_transaction_buffer_release(struct binder_proc *proc,
> struct binder_thread *thread,
> struct binder_buffer *buffer,
> - binder_size_t failed_at,
> + binder_size_t off_end_offset,
> bool is_failure)
> {
> int debug_id = buffer->debug_id;
> - binder_size_t off_start_offset, buffer_offset, off_end_offset;
> + binder_size_t off_start_offset, buffer_offset;
>
> binder_debug(BINDER_DEBUG_TRANSACTION,
> "%d buffer release %d, size %zd-%zd, failed at %llx\n",
> proc->pid, buffer->debug_id,
> buffer->data_size, buffer->offsets_size,
> - (unsigned long long)failed_at);
> + (unsigned long long)off_end_offset);
>
> if (buffer->target_node)
> binder_dec_node(buffer->target_node, 1, 0);
>
> off_start_offset = ALIGN(buffer->data_size, sizeof(void *));
> - off_end_offset = is_failure && failed_at ? failed_at :
> - off_start_offset + buffer->offsets_size;
> +
> for (buffer_offset = off_start_offset; buffer_offset < off_end_offset;
> buffer_offset += sizeof(binder_size_t)) {
> struct binder_object_header *hdr;
> @@ -2111,6 +2110,21 @@ static void binder_transaction_buffer_release(struct binder_proc *proc,
> }
> }
>
> +/* Clean up all the objects in the buffer */
> +static inline void binder_release_entire_buffer(struct binder_proc *proc,
> + struct binder_thread *thread,
> + struct binder_buffer *buffer,
> + bool is_failure)
> +{
> + binder_size_t off_end_offset;
> +
> + off_end_offset = ALIGN(buffer->data_size, sizeof(void *));
> + off_end_offset += buffer->offsets_size;
> +
> + binder_transaction_buffer_release(proc, thread, buffer,
> + off_end_offset, is_failure);
> +}
> +
> static int binder_translate_binder(struct flat_binder_object *fp,
> struct binder_transaction *t,
> struct binder_thread *thread)
> @@ -2806,7 +2820,7 @@ static int binder_proc_transaction(struct binder_transaction *t,
> t_outdated->buffer = NULL;
> buffer->transaction = NULL;
> trace_binder_transaction_update_buffer_release(buffer);
> - binder_transaction_buffer_release(proc, NULL, buffer, 0, 0);
> + binder_release_entire_buffer(proc, NULL, buffer, false);
> binder_alloc_free_buf(&proc->alloc, buffer);
> kfree(t_outdated);
> binder_stats_deleted(BINDER_STAT_TRANSACTION);
> @@ -3775,7 +3789,7 @@ binder_free_buf(struct binder_proc *proc,
> binder_node_inner_unlock(buf_node);
> }
> trace_binder_transaction_buffer_release(buffer);
> - binder_transaction_buffer_release(proc, thread, buffer, 0, is_failure);
> + binder_release_entire_buffer(proc, thread, buffer, is_failure);
> binder_alloc_free_buf(&proc->alloc, buffer);
> }
>
> --
> 2.40.1.521.gf1e218fcd8-goog
>
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