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Message-ID: <dd53f11a-ae6f-79af-2ea2-8091d1c4f15e@linaro.org>
Date: Mon, 15 Nov 2021 08:38:38 -0800
From: Tadeusz Struk <tadeusz.struk@...aro.org>
To: Jens Axboe <axboe@...nel.dk>
Cc: Alexander Viro <viro@...iv.linux.org.uk>, io-uring@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
stable@...r.kernel.org,
syzbot+6055980d041c8ac23307@...kaller.appspotmail.com
Subject: Re: [PATCH] io_uring: prevent io_put_identity() from freeing a static
identity
On 11/3/21 18:21, Tadeusz Struk wrote:
> Note: this applies to 5.10 stable only. It doesn't trigger on anything
> above 5.10 as the code there has been substantially reworked. This also
> doesn't apply to any stable kernel below 5.10 afaict.
>
> Syzbot found a bug: KASAN: invalid-free in io_dismantle_req
> https://syzkaller.appspot.com/bug?id=123d9a852fc88ba573ffcb2dbcf4f9576c3b0559
>
> The test submits bunch of io_uring writes and exits, which then triggers
> uring_task_cancel() and io_put_identity(), which in some corner cases,
> tries to free a static identity. This causes a panic as shown in the
> trace below:
>
> BUG: KASAN: double-free or invalid-free in kfree+0xd5/0x310
> CPU: 0 PID: 4618 Comm: repro Not tainted 5.10.76-05281-g4944ec82ebb9-dirty #17
> Call Trace:
> dump_stack_lvl+0x1b2/0x21b
> print_address_description+0x8d/0x3b0
> kasan_report_invalid_free+0x58/0x130
> ____kasan_slab_free+0x14b/0x170
> __kasan_slab_free+0x11/0x20
> slab_free_freelist_hook+0xcc/0x1a0
> kfree+0xd5/0x310
> io_dismantle_req+0x9b0/0xd90
> io_do_iopoll+0x13a4/0x23e0
> io_iopoll_try_reap_events+0x116/0x290
> io_uring_cancel_task_requests+0x197d/0x1ee0
> io_uring_flush+0x170/0x6d0
> filp_close+0xb0/0x150
> put_files_struct+0x1d4/0x350
> exit_files+0x80/0xa0
> do_exit+0x6d9/0x2390
> do_group_exit+0x16a/0x2d0
> get_signal+0x133e/0x1f80
> arch_do_signal+0x7b/0x610
> exit_to_user_mode_prepare+0xaa/0xe0
> syscall_exit_to_user_mode+0x24/0x40
> do_syscall_64+0x3d/0x70
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Allocated by task 4611:
> ____kasan_kmalloc+0xcd/0x100
> __kasan_kmalloc+0x9/0x10
> kmem_cache_alloc_trace+0x208/0x390
> io_uring_alloc_task_context+0x57/0x550
> io_uring_add_task_file+0x1f7/0x290
> io_uring_create+0x2195/0x3490
> __x64_sys_io_uring_setup+0x1bf/0x280
> do_syscall_64+0x31/0x70
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> The buggy address belongs to the object at ffff88810732b500
> which belongs to the cache kmalloc-192 of size 192
> The buggy address is located 88 bytes inside of
> 192-byte region [ffff88810732b500, ffff88810732b5c0)
> Kernel panic - not syncing: panic_on_warn set ...
>
> This issue bisected to this commit:
> commit 186725a80c4e ("io_uring: fix skipping disabling sqo on exec")
>
> Simple reverting the offending commit doesn't work as it hits some
> other, related issues like:
>
> /* sqo_dead check is for when this happens after cancellation */
> WARN_ON_ONCE(ctx->sqo_task == current && !ctx->sqo_dead &&
> !xa_load(&tctx->xa, (unsigned long)file));
>
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 5622 at fs/io_uring.c:8960 io_uring_flush+0x5bc/0x6d0
> Modules linked in:
> CPU: 1 PID: 5622 Comm: repro Not tainted 5.10.76-05281-g4944ec82ebb9-dirty #16
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-6.fc35 04/01/2014
> RIP: 0010:io_uring_flush+0x5bc/0x6d0
> Call Trace:
> filp_close+0xb0/0x150
> put_files_struct+0x1d4/0x350
> reset_files_struct+0x88/0xa0
> bprm_execve+0x7f2/0x9f0
> do_execveat_common+0x46f/0x5d0
> __x64_sys_execve+0x92/0xb0
> do_syscall_64+0x31/0x70
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Changing __io_uring_task_cancel() to call io_disable_sqo_submit() directly,
> as the comment suggests, only if __io_uring_files_cancel() is not executed
> seems to fix the issue.
>
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Cc: <io-uring@...r.kernel.org>
> Cc: <linux-fsdevel@...r.kernel.org>
> Cc: <linux-kernel@...r.kernel.org>
> Cc: <stable@...r.kernel.org>
> Reported-by: syzbot+6055980d041c8ac23307@...kaller.appspotmail.com
> Signed-off-by: Tadeusz Struk <tadeusz.struk@...aro.org>
> ---
> fs/io_uring.c | 21 +++++++++++++++++----
> 1 file changed, 17 insertions(+), 4 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 0736487165da..fcf9ffe9b209 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -8882,20 +8882,18 @@ void __io_uring_task_cancel(void)
> struct io_uring_task *tctx = current->io_uring;
> DEFINE_WAIT(wait);
> s64 inflight;
> + int canceled = 0;
>
> /* make sure overflow events are dropped */
> atomic_inc(&tctx->in_idle);
>
> - /* trigger io_disable_sqo_submit() */
> - if (tctx->sqpoll)
> - __io_uring_files_cancel(NULL);
> -
> do {
> /* read completions before cancelations */
> inflight = tctx_inflight(tctx);
> if (!inflight)
> break;
> __io_uring_files_cancel(NULL);
> + canceled = 1;
>
> prepare_to_wait(&tctx->wait, &wait, TASK_UNINTERRUPTIBLE);
>
> @@ -8909,6 +8907,21 @@ void __io_uring_task_cancel(void)
> finish_wait(&tctx->wait, &wait);
> } while (1);
>
> + /*
> + * trigger io_disable_sqo_submit()
> + * if not already done by __io_uring_files_cancel()
> + */
> + if (tctx->sqpoll && !canceled) {
> + struct file *file;
> + unsigned long index;
> +
> + xa_for_each(&tctx->xa, index, file) {
> + struct io_ring_ctx *ctx = file->private_data;
> +
> + io_disable_sqo_submit(ctx);
> + }
> + }
> +
> atomic_dec(&tctx->in_idle);
>
> io_uring_remove_task_files(tctx);
>
Hi,
Any comments on this one? It needs to be ACK'ed by the maintainer before
it is applied to 5.10 stable.
--
Thanks,
Tadeusz
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