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Subject: Re: [PATCH 2/2] arch: add pidfd and io_uring syscalls everywhere
To:     Will Deacon <will.deacon@arm.com>
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        Arnd Bergmann <arnd@arndb.de>,
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From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <032faa2f-6317-75b6-8514-076ef1a244e8@kernel.dk>
Date:   Wed, 3 Apr 2019 09:39:52 -0600
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On 4/3/19 9:19 AM, Will Deacon wrote:
> Hi Jens,
> 
> 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?


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