On 02/12/2020 11:31, Xiaoguang Wang wrote:
> Abaci Fuzz reported a double-free or invalid-free BUG in io_commit_cqring():
> [ 95.504842] BUG: KASAN: double-free or invalid-free in io_commit_cqring+0x3ec/0x8e0
> [ 95.505921]
> [ 95.506225] CPU: 0 PID: 4037 Comm: io_wqe_worker-0 Tainted: G B
> W 5.10.0-rc5+ #1
> [ 95.507434] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
> [ 95.508248] Call Trace:
> [ 95.508683] dump_stack+0x107/0x163
> [ 95.509323] ? io_commit_cqring+0x3ec/0x8e0
> [ 95.509982] print_address_description.constprop.0+0x3e/0x60
> [ 95.510814] ? vprintk_func+0x98/0x140
> [ 95.511399] ? io_commit_cqring+0x3ec/0x8e0
> [ 95.512036] ? io_commit_cqring+0x3ec/0x8e0
> [ 95.512733] kasan_report_invalid_free+0x51/0x80
> [ 95.513431] ? io_commit_cqring+0x3ec/0x8e0
> [ 95.514047] __kasan_slab_free+0x141/0x160
> [ 95.514699] kfree+0xd1/0x390
> [ 95.515182] io_commit_cqring+0x3ec/0x8e0
> [ 95.515799] __io_req_complete.part.0+0x64/0x90
> [ 95.516483] io_wq_submit_work+0x1fa/0x260
> [ 95.517117] io_worker_handle_work+0xeac/0x1c00
> [ 95.517828] io_wqe_worker+0xc94/0x11a0
> [ 95.518438] ? io_worker_handle_work+0x1c00/0x1c00
> [ 95.519151] ? __kthread_parkme+0x11d/0x1d0
> [ 95.519806] ? io_worker_handle_work+0x1c00/0x1c00
> [ 95.520512] ? io_worker_handle_work+0x1c00/0x1c00
> [ 95.521211] kthread+0x396/0x470
> [ 95.521727] ? _raw_spin_unlock_irq+0x24/0x30
> [ 95.522380] ? kthread_mod_delayed_work+0x180/0x180
> [ 95.523108] ret_from_fork+0x22/0x30
> [ 95.523684]
> [ 95.523985] Allocated by task 4035:
> [ 95.524543] kasan_save_stack+0x1b/0x40
> [ 95.525136] __kasan_kmalloc.constprop.0+0xc2/0xd0
> [ 95.525882] kmem_cache_alloc_trace+0x17b/0x310
> [ 95.533930] io_queue_sqe+0x225/0xcb0
> [ 95.534505] io_submit_sqes+0x1768/0x25f0
> [ 95.535164] __x64_sys_io_uring_enter+0x89e/0xd10
> [ 95.535900] do_syscall_64+0x33/0x40
> [ 95.536465] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [ 95.537199]
> [ 95.537505] Freed by task 4035:
> [ 95.538003] kasan_save_stack+0x1b/0x40
> [ 95.538599] kasan_set_track+0x1c/0x30
> [ 95.539177] kasan_set_free_info+0x1b/0x30
> [ 95.539798] __kasan_slab_free+0x112/0x160
> [ 95.540427] kfree+0xd1/0x390
> [ 95.540910] io_commit_cqring+0x3ec/0x8e0
> [ 95.541516] io_iopoll_complete+0x914/0x1390
> [ 95.542150] io_do_iopoll+0x580/0x700
> [ 95.542724] io_iopoll_try_reap_events.part.0+0x108/0x200
> [ 95.543512] io_ring_ctx_wait_and_kill+0x118/0x340
> [ 95.544206] io_uring_release+0x43/0x50
> [ 95.544791] __fput+0x28d/0x940
> [ 95.545291] task_work_run+0xea/0x1b0
> [ 95.545873] do_exit+0xb6a/0x2c60
> [ 95.546400] do_group_exit+0x12a/0x320
> [ 95.546967] __x64_sys_exit_group+0x3f/0x50
> [ 95.547605] do_syscall_64+0x33/0x40
> [ 95.548155] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> The reason is that once we got a non EAGAIN error in io_wq_submit_work(),
> we'll complete req by calling io_req_complete(), which will hold completion_lock
> to call io_commit_cqring(), but for polled io, io_iopoll_complete() won't
> hold completion_lock to call io_commit_cqring(), then there maybe concurrent
> access to ctx->defer_list, double free may happen.
>
> To fix this bug, we always let io_iopoll_complete() complete polled io.
It makes sense if it got there though means of REQ_F_FORCE_ASYNC or as a linked,
but a thing I'm afraid of is going twice through the end section of io_issue_sqe()
(i.e. io_iopoll_req_issued). Shouldn't happen though.
Reviewed-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
>
> Reported-by: Abaci Fuzz <abaci@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Xiaoguang Wang <xiaoguang.wang@xxxxxxxxxxxxxxxxx>
> ---
> fs/io_uring.c | 15 +++++++++++++--
> 1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index a8c136a..901ca67 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -6074,8 +6074,19 @@ static struct io_wq_work *io_wq_submit_work(struct io_wq_work *work)
> }
>
> if (ret) {
> - req_set_fail_links(req);
> - io_req_complete(req, ret);
> + /*
> + * io_iopoll_complete() does not hold completion_lock to complete
> + * polled io, so here for polled io, just mark it done and still let
> + * io_iopoll_complete() complete it.
> + */
> + if (req->ctx->flags & IORING_SETUP_IOPOLL) {
> + struct kiocb *kiocb = &req->rw.kiocb;
> +
> + kiocb_done(kiocb, ret, NULL);
> + } else {
> + req_set_fail_links(req);
> + io_req_complete(req, ret);
> + }
> }
>
> return io_steal_work(req);
>
--
Pavel Begunkov
