From: Bart Van Assche <bvanassche@acm.org>
To: dgilbert@interlog.com,
SCSI development list <linux-scsi@vger.kernel.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Cc: "Martin K. Petersen" <martin.petersen@ORACLE.COM>,
USB list <linux-usb@vger.kernel.org>
Subject: Re: lib/scatterlist.c : sgl_alloc_order promises more than it delivers
Date: Thu, 24 Sep 2020 19:34:08 -0700 [thread overview]
Message-ID: <d9513f73-fa18-4b71-fabf-be0b9e1614fd@acm.org> (raw)
In-Reply-To: <b9f5c065-7662-30e0-8cbd-27a77d28611e@interlog.com>
On 2020-09-24 18:46, Douglas Gilbert wrote:
> /* Check for integer overflow */
> if (length > (nent << (PAGE_SHIFT + order)))
> return NULL;
>
> Well _integers_ don't wrap, but that pedantic point aside, 'nent' is an
> unsigned int which means the rhs expression cannot represent 2^32 or
> higher. So if length >= 2^32 the function fails (i.e. returns NULL).
>
> On 8 GiB and 16 GiB machines I can easily build 6 or 12 GiB sgl_s (with
> scsi_debug) but only if no single allocation is >= 4 GiB due to the
> above check.
>
> So is the above check intended to do that or is it a bug?
The above check verifies that nent << (PAGE_SHIFT + order) ==
(uint64_t)nent << (PAGE_SHIFT + order). So I think it does what the
comment says it does.
Bart.
next prev parent reply other threads:[~2020-09-25 2:34 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-25 1:46 lib/scatterlist.c : sgl_alloc_order promises more than it delivers Douglas Gilbert
2020-09-25 2:34 ` Bart Van Assche [this message]
2020-09-25 4:55 ` Douglas Gilbert
2020-09-26 4:32 ` Bart Van Assche
2020-10-11 21:21 ` Douglas Gilbert
2020-10-11 22:24 ` Bart Van Assche
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