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[86.27.177.88]) by smtp.gmail.com with ESMTPSA id b5-20020a05600c4e0500b00397243d3dbcsm2592590wmq.31.2022.05.19.02.26.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 May 2022 02:26:13 -0700 (PDT) Date: Thu, 19 May 2022 10:26:11 +0100 From: Lee Jones To: Jens Axboe Cc: Pavel Begunkov , io-uring@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [REPORT] Use-after-free Read in __fdget_raw in v5.10.y Message-ID: 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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <38f63cda-b208-0d83-6aec-25115bd1c021@kernel.dk> Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org 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? -- Lee Jones [李琼斯] Principal Technical Lead - Developer Services Linaro.org │ Open source software for Arm SoCs Follow Linaro: Facebook | Twitter | Blog