linux-kernel - Re: int overflow in io

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Date:	Wed, 16 Dec 2015 13:56:18 +0100
From:	Jan Kara <jack@...e.cz>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	Benjamin LaHaise <bcrl@...ck.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-aio <linux-aio@...ck.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	syzkaller <syzkaller@...glegroups.com>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>
Subject: Re: int overflow in io_getevents

On Mon 07-12-15 11:27:07, Dmitry Vyukov wrote:
> Hello,
> 
> While running syzkaller fuzzer on commit
> 31ade3b83e1821da5fbb2f11b5b3d4ab2ec39db8, I've hit the following UBSAN
> warning. I think it can lead to an unexpected active wait loop, if
> user-space expects such io_getevents to wait for a long duration but
> instead it returns immediately, so user-space reissues the same call
> again and again. Andrey suggested that read_events should validate
> timeout with timespec_valid_strict before using it.

Yup, looks correct. Will you send a patch?

								Honza

> UBSAN: Undefined behaviour in include/linux/ktime.h:55:49
> signed integer overflow:
> 1449363382000000000 + 8584381026499825158 cannot be represented in
> type 'long long int'
> CPU: 0 PID: 27992 Comm: syzkaller_execu Not tainted 4.4.0-rc3+ #150
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>  0000000000000000 ffff880062ab7ae0 ffffffff82c6f2a8 0000000041b58ab3
>  ffffffff8788bf8d ffffffff82c6f1f6 ffff880062ab7aa8 ffffffff88479680
>  ffff880062ab7be0 7721d90fc5200e06 0000000000000001 ffff880062ab7af0
> Call Trace:
>  [<     inline     >] __dump_stack lib/dump_stack.c:15
>  [<ffffffff82c6f2a8>] dump_stack+0xb2/0xfa lib/dump_stack.c:50
>  [<ffffffff82d622e7>] ubsan_epilogue+0x12/0x8f lib/ubsan.c:160
>  [<ffffffff82d63e58>] handle_overflow+0x22f/0x276 lib/ubsan.c:191
>  [<ffffffff82d63ec9>] __ubsan_handle_add_overflow+0x2a/0x31 lib/ubsan.c:199
>  [<     inline     >] ktime_set include/linux/ktime.h:55
>  [<     inline     >] timespec_to_ktime include/linux/ktime.h:83
>  [<ffffffff8190ca77>] read_events+0x4b7/0x560 fs/aio.c:1273
>  [<     inline     >] SYSC_io_getevents fs/aio.c:1737
>  [<ffffffff81913567>] SyS_io_getevents+0xc7/0x340 fs/aio.c:1726
>  [<ffffffff868dae76>] entry_SYSCALL_64_fastpath+0x16/0x7a
> arch/x86/entry/entry_64.S:185
> 
> Thank you
> --
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-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR
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