linux-kernel - RE: [PATCH] mm: mmap() sometimes succeeds even if the region to map is invalid.

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Date:	Fri, 17 Feb 2012 14:34:13 +0530
From:	Venu Byravarasu <vbyravarasu@...dia.com>
To:	Naotaka Hamaguchi <n.hamaguchi@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
CC:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Subject: RE: [PATCH] mm: mmap() sometimes succeeds even if the region to map
 is invalid.

> The detail of these problems is as follows:

> 1. mmap() succeeds even if "offset" argument is a negative value, although
>    it should return EINVAL in such case.

> In such case, it is actually regarded as big positive value
> because the type of "off" is "unsigned long" in the kernel.
> For example, off=-4096 (-0x1000) is regarded as
> off = 0xfffffffffffff000 (x86_64) and as off = 0xfffff000 (x86).
> It results in mapping too big offset region.

It is not true always.

Considering your example, say if page size is 4k, then PAGE_MASK = 0xFFF
hence (off & ~PAGE_MASK) will be true and " -EINVAL" will be returned.
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