On 02/12/2020 17:00, Pavel Begunkov wrote:
> 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.
This one can use a test by the way. E.g. sending a bunch of iopoll requests,
both generic and REQ_F_FORCE_ASYNC, and expect it not to fail.
>
> 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
