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Date:   Wed, 3 Apr 2019 16:49:02 +0100
From:   Will Deacon <will.deacon@arm.com>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        Arnd Bergmann <arnd@arndb.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Richard Henderson <rth@twiddle.net>,
        Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
        Matt Turner <mattst88@gmail.com>,
        Russell King <linux@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Tony Luck <tony.luck@intel.com>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Michal Simek <monstr@monstr.eu>,
        Ralf Baechle <ralf@linux-mips.org>,
        Paul Burton <paul.burton@mips.com>,
        James Hogan <jhogan@kernel.org>,
        "James E . J . Bottomley" <James.Bottomley@HansenPartnership.com>,
        Helge Deller <deller@gmx.de>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
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Subject: Re: [PATCH 2/2] arch: add pidfd and io_uring syscalls everywhere
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On Wed, Apr 03, 2019 at 09:39:52AM -0600, Jens Axboe wrote:
> On 4/3/19 9:19 AM, Will Deacon wrote:
> > On Wed, Apr 03, 2019 at 07:49:26AM -0600, Jens Axboe wrote:
> >> On 4/3/19 5:11 AM, Will Deacon wrote:
> >>> will@autoplooker:~/liburing/test$ ./io_uring_register 
> >>> RELIMIT_MEMLOCK: 67108864 (67108864)
> >>> [   35.477875] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000070
> >>> [   35.478969] Mem abort info:
> >>> [   35.479296]   ESR = 0x96000004
> >>> [   35.479785]   Exception class = DABT (current EL), IL = 32 bits
> >>> [   35.480528]   SET = 0, FnV = 0
> >>> [   35.480980]   EA = 0, S1PTW = 0
> >>> [   35.481345] Data abort info:
> >>> [   35.481680]   ISV = 0, ISS = 0x00000004
> >>> [   35.482267]   CM = 0, WnR = 0
> >>> [   35.482618] user pgtable: 4k pages, 48-bit VAs, pgdp = (____ptrval____)
> >>> [   35.483486] [0000000000000070] pgd=0000000000000000
> >>> [   35.484041] Internal error: Oops: 96000004 [#1] PREEMPT SMP
> >>> [   35.484788] Modules linked in:
> >>> [   35.485311] CPU: 113 PID: 3973 Comm: io_uring_regist Not tainted 5.1.0-rc3-00012-g40b114779944 #1
> >>> [   35.486712] Hardware name: linux,dummy-virt (DT)
> >>> [   35.487450] pstate: 20400005 (nzCv daif +PAN -UAO)
> >>> [   35.488228] pc : link_pwq+0x10/0x60
> >>> [   35.488794] lr : apply_wqattrs_commit+0xe0/0x118
> >>> [   35.489550] sp : ffff000017e2bbc0
> >>
> >> Huh, this looks odd, it's crashing inside the wq setup.
> > 
> > Enabling KASAN seems to indicate a double-free, which may well be related.
> 
> Does this help?

Yes, thanks for the quick patch. Feel free to add:

Reported-by: Will Deacon <will.deacon@arm.com>
Tested-by: Will Deacon <will.deacon@arm.com>

if you spin a proper patch.

Will

> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index bbdbd56cf2ac..07d6ef195d05 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -2215,6 +2215,7 @@ static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
>  			fput(ctx->user_files[i]);
>  
>  		kfree(ctx->user_files);
> +		ctx->user_files = NULL;
>  		ctx->nr_user_files = 0;
>  		return ret;
>  	}
> 
> -- 
> Jens Axboe
>