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Thu, 19 May 2022 05:13:42 -0700 (PDT) Received: from [192.168.1.100] ([198.8.77.157]) by smtp.gmail.com with ESMTPSA id a12-20020a62d40c000000b0050dc7628178sm4111654pfh.82.2022.05.19.05.13.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 May 2022 05:13:41 -0700 (PDT) Message-ID: <73db78f5-ea6c-2693-877e-976703bbfead@kernel.dk> Date: Thu, 19 May 2022 06:13:40 -0600 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:91.0) Gecko/20100101 Thunderbird/91.8.1 Subject: Re: [REPORT] Use-after-free Read in __fdget_raw in v5.10.y Content-Language: en-US To: Lee Jones Cc: Pavel Begunkov , io-uring@vger.kernel.org, linux-kernel@vger.kernel.org References: <06710b30-fec8-b593-3af4-1318515b41d8@kernel.dk> <49609b89-f2f0-44b3-d732-dfcb4f73cee1@kernel.dk> <1e64d20a-42cc-31cd-0fd8-2718dd8b1f31@kernel.dk> <38f63cda-b208-0d83-6aec-25115bd1c021@kernel.dk> From: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 5/19/22 3:26 AM, Lee Jones wrote: > On Wed, 18 May 2022, Jens Axboe wrote: > >> On 5/18/22 10:34 AM, Lee Jones wrote: >>> On Wed, 18 May 2022, Jens Axboe wrote: >>> >>>> On 5/18/22 09:39, Lee Jones wrote: >>>>> On Wed, 18 May 2022, Jens Axboe wrote: >>>>> >>>>>> On 5/18/22 9:14 AM, Lee Jones wrote: >>>>>>> On Wed, 18 May 2022, Jens Axboe wrote: >>>>>>> >>>>>>>> On 5/18/22 6:54 AM, Jens Axboe wrote: >>>>>>>>> On 5/18/22 6:52 AM, Jens Axboe wrote: >>>>>>>>>> On 5/18/22 6:50 AM, Lee Jones wrote: >>>>>>>>>>> On Tue, 17 May 2022, Jens Axboe wrote: >>>>>>>>>>> >>>>>>>>>>>> On 5/17/22 7:00 AM, Lee Jones wrote: >>>>>>>>>>>>> On Tue, 17 May 2022, Jens Axboe wrote: >>>>>>>>>>>>> >>>>>>>>>>>>>> On 5/17/22 6:36 AM, Lee Jones wrote: >>>>>>>>>>>>>>> On Tue, 17 May 2022, Jens Axboe wrote: >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> On 5/17/22 6:24 AM, Lee Jones wrote: >>>>>>>>>>>>>>>>> On Tue, 17 May 2022, Jens Axboe wrote: >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> On 5/17/22 5:41 AM, Lee Jones wrote: >>>>>>>>>>>>>>>>>>> Good afternoon Jens, Pavel, et al., >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> Not sure if you are presently aware, but there appears to be a >>>>>>>>>>>>>>>>>>> use-after-free issue affecting the io_uring worker driver (fs/io-wq.c) >>>>>>>>>>>>>>>>>>> in Stable v5.10.y. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> The full sysbot report can be seen below [0]. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> The C-reproducer has been placed below that [1]. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> I had great success running this reproducer in an infinite loop. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> My colleague reverse-bisected the fixing commit to: >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> commit fb3a1f6c745ccd896afadf6e2d6f073e871d38ba >>>>>>>>>>>>>>>>>>> Author: Jens Axboe >>>>>>>>>>>>>>>>>>> Date: Fri Feb 26 09:47:20 2021 -0700 >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> io-wq: have manager wait for all workers to exit >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> Instead of having to wait separately on workers and manager, just have >>>>>>>>>>>>>>>>>>> the manager wait on the workers. We use an atomic_t for the reference >>>>>>>>>>>>>>>>>>> here, as we need to start at 0 and allow increment from that. Since the >>>>>>>>>>>>>>>>>>> number of workers is naturally capped by the allowed nr of processes, >>>>>>>>>>>>>>>>>>> and that uses an int, there is no risk of overflow. >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> Signed-off-by: Jens Axboe >>>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>>> fs/io-wq.c | 30 ++++++++++++++++++++++-------- >>>>>>>>>>>>>>>>>>> 1 file changed, 22 insertions(+), 8 deletions(-) >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> Does this fix it: >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> commit 886d0137f104a440d9dfa1d16efc1db06c9a2c02 >>>>>>>>>>>>>>>>>> Author: Jens Axboe >>>>>>>>>>>>>>>>>> Date: Fri Mar 5 12:59:30 2021 -0700 >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> io-wq: fix race in freeing 'wq' and worker access >>>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>>> Looks like it didn't make it into 5.10-stable, but we can certainly >>>>>>>>>>>>>>>>>> rectify that. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> Thanks for your quick response Jens. >>>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> This patch doesn't apply cleanly to v5.10.y. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> This is probably why it never made it into 5.10-stable :-/ >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Right. It doesn't apply at all unfortunately. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>>> I'll have a go at back-porting it. Please bear with me. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Let me know if you into issues with that and I can help out. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> I think the dependency list is too big. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Too much has changed that was never back-ported. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Actually the list of patches pertaining to fs/io-wq.c alone isn't so >>>>>>>>>>>>>>> bad, I did start to back-port them all but some of the big ones have >>>>>>>>>>>>>>> fs/io_uring.c changes incorporated and that list is huge (256 patches >>>>>>>>>>>>>>> from v5.10 to the fixing patch mentioned above). >>>>>>>>>>>>>> >>>>>>>>>>>>>> The problem is that 5.12 went to the new worker setup, and this patch >>>>>>>>>>>>>> landed after that even though it also applies to the pre-native workers. >>>>>>>>>>>>>> Hence the dependency chain isn't really as long as it seems, probably >>>>>>>>>>>>>> just a few patches backporting the change references and completions. >>>>>>>>>>>>>> >>>>>>>>>>>>>> I'll take a look this afternoon. >>>>>>>>>>>>> >>>>>>>>>>>>> Thanks Jens. I really appreciate it. >>>>>>>>>>>> >>>>>>>>>>>> Can you see if this helps? Untested... >>>>>>>>>>> >>>>>>>>>>> What base does this apply against please? >>>>>>>>>>> >>>>>>>>>>> I tried Mainline and v5.10.116 and both failed. >>>>>>>>>> >>>>>>>>>> It's against 5.10.116, so that's puzzling. Let me double check I sent >>>>>>>>>> the right one... >>>>>>>>> >>>>>>>>> Looks like I sent the one from the wrong directory, sorry about that. >>>>>>>>> This one should be better: >>>>>>>> >>>>>>>> Nope, both are the right one. Maybe your mailer is mangling the patch? >>>>>>>> I'll attach it gzip'ed here in case that helps. >>>>>>> >>>>>>> Okay, that applied, thanks. >>>>>>> >>>>>>> Unfortunately, I am still able to crash the kernel in the same way. >>>>>> >>>>>> Alright, maybe it's not enough. I can't get your reproducer to crash, >>>>>> unfortunately. I'll try on a different box. >>>>> >>>>> You need to have fuzzing and kasan enabled. >>>> >>>> I do have kasan enabled. What's fuzzing? >>> >>> CONFIG_KCOV >> >> Ah ok - I don't think that's needed for this. >> >> Looking a bit deeper at this, I'm now convinced your bisect went off the >> rails at some point. Probably because this can be timing specific. >> >> Can you try with this patch? >> >> >> diff --git a/fs/io_uring.c b/fs/io_uring.c >> index 4330603eae35..3ecf71151fb1 100644 >> --- a/fs/io_uring.c >> +++ b/fs/io_uring.c >> @@ -4252,12 +4252,8 @@ static int io_statx(struct io_kiocb *req, bool force_nonblock) >> struct io_statx *ctx = &req->statx; >> int ret; >> >> - if (force_nonblock) { >> - /* only need file table for an actual valid fd */ >> - if (ctx->dfd == -1 || ctx->dfd == AT_FDCWD) >> - req->flags |= REQ_F_NO_FILE_TABLE; >> + if (force_nonblock) >> return -EAGAIN; >> - } >> >> ret = do_statx(ctx->dfd, ctx->filename, ctx->flags, ctx->mask, >> ctx->buffer); > > This does appear to solve the issue. :) > > Thanks so much for working on this. > > What are the next steps? > > Are you able to submit this to Stable? Yes, I'll get it queued up for stable. -- Jens Axboe