linux-kernel - Re: int overflow in io

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Date:	Thu, 7 Jan 2016 10:31:32 -0500
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	Dmitry Vyukov <dvyukov@...gle.com>
Cc:	Jan Kara <jack@...e.cz>, 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 Thu, Jan 07, 2016 at 10:12:02AM +0100, Dmitry Vyukov wrote:
...
> Sorry, but the following program still prints -9223372036562067969. I
> think timespec_valid check will do.

Ah, right.  Yes, using timespec_valid() instead of  timespec_valid_strict() 
as initially proposed will address my concerns.  Updated commit below.

		-ben
-- 
"Thought is the essence of where you are now."

commit 3a55c535cf3836257434518bd6bc11464c493492
Author: Benjamin LaHaise <bcrl@...ck.org>
Date:   Thu Jan 7 10:25:44 2016 -0500

    aio: handle integer overflow in io_getevents() timespec usage
    
    Dmitry Vyukov reported an integer overflow in io_getevents() when
    running a fuzzer.  Upon investigation, the triggers appears to be that
    an invalid value for the tv_sec or tv_nsec was passed in which is not
    handled by timespec_to_ktime().  This patch fixes that by making
    io_getevents() return -EINVAL when timespec_valid() checks fail.  We
    use timespec_valid() instead of timespec_valid_strict() to avoid issues
    caused by userspace not knowing the cutoff for KTIME_SEC_MAX.
    
    Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
    Signed-off-by: Benjamin LaHaise <bcrl@...ck.org>

diff --git a/fs/aio.c b/fs/aio.c
index 155f842..d161a2f 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1269,6 +1269,8 @@ static long read_events(struct kioctx *ctx, long min_nr, long nr,
 
 		if (unlikely(copy_from_user(&ts, timeout, sizeof(ts))))
 			return -EFAULT;
+		if (!timespec_valid())
+			return -EINVAL;
 
 		until = timespec_to_ktime(ts);
 	}
--
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