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Message-ID: <2cd473d4-734d-95e2-4f3f-d793d065c449@linaro.org>
Date: Wed, 15 Dec 2021 12:27:37 -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 11/15/21 08:38, Tadeusz Struk wrote:
> 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.
>
This still triggers on 5.10.85. Anyone want to have a look?
--
Thanks,
Tadeusz
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