Re: [PATCH 2/2] arch: add pidfd and io_uring syscalls everywhere

Will Deacon
2019-04-03T15:49:02Z

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\000000000000000
> >>> [ 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
>