linux-kernel - Re: [PATCH] mm: mmap system call does not return EOVERFLOW

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Date:	Thu, 22 Dec 2011 11:58:13 -0500
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Naotaka Hamaguchi <n.hamaguchi@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: mmap system call does not return EOVERFLOW

> To fix this bug, it is necessary to compare "off" plus "len"
> with "off" by units of "off_t". The patch is here:
>
> Signed-off-by: Naotaka Hamaguchi <n.hamaguchi@...fujitsu.com>
> ---
>  mm/mmap.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index eae90af..e74e736 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -948,6 +948,7 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
>        vm_flags_t vm_flags;
>        int error;
>        unsigned long reqprot = prot;
> +       off_t off = pgoff << PAGE_SHIFT;
>
>        /*
>         * Does the application expect PROT_READ to imply PROT_EXEC?
> @@ -971,7 +972,7 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
>                return -ENOMEM;
>
>        /* offset overflow? */
> -       if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
> +       if ((off + len) < off)
>                return -EOVERFLOW;

Hmm...
pgoff doesn't make actual overflow. do_mmap_pgoff() can calculate big
value. We have
no reason to make artificial limit. Why don't you meke a overflow
check in sys_mmap()?
--
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