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