linux-kernel - Re: [PATCH] proc-vmcore: wrong data type casting fix

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Message-ID: <20160311083133.GA3207@x1.redhat.com>
Date:	Fri, 11 Mar 2016 16:31:33 +0800
From:	Baoquan He <bhe@...hat.com>
To:	Dave Young <dyoung@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, d.hatayama@...fujitsu.com,
	vgoyal@...hat.com, kexec@...ts.infradead.org, nasa4836@...il.com
Subject: Re: [PATCH] proc-vmcore: wrong data type casting fix

On 03/11/16 at 04:15pm, Dave Young wrote:
> On i686 PAE enabled machine the contiguous physical area could be large
> and it can cause triming down variables in below calculation in
> read_vmcore() and mmap_vmcore():
> 
> 	tsz = min_t(size_t, m->offset + m->size - *fpos, buflen);
> 
> Then the real size passed down is not correct any more.
> Suppose m->offset + m->size - *fpos being truncated to 0, buflen >0 then
> we will get tsz = 0. It is of course not an expected result.
> 
> During out test there are two problems caused by it:
	  ~ our
> 1) read_vmcore will refuse to continue so makedumpfile fails.
> 2) mmap_vmcore will trigger BUG_ON() in remap_pfn_range().
> 
> Use unsigned long long in min_t instead so that the variables are not
> truncated.
> 
> Signed-off-by: Baoquan He <bhe@...hat.com>
> Signed-off-by: Dave Young <dyoung@...hat.com>
> ---
>  fs/proc/vmcore.c |    7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> --- linux-x86.orig/fs/proc/vmcore.c
> +++ linux-x86/fs/proc/vmcore.c
> @@ -231,7 +231,9 @@ static ssize_t __read_vmcore(char *buffe
>  
>  	list_for_each_entry(m, &vmcore_list, list) {
>  		if (*fpos < m->offset + m->size) {
> -			tsz = min_t(size_t, m->offset + m->size - *fpos, buflen);
> +			tsz = (size_t)min_t(unsigned long long,
> +					    m->offset + m->size - *fpos,
> +					    buflen);
>  			start = m->paddr + *fpos - m->offset;
>  			tmp = read_from_oldmem(buffer, tsz, &start, userbuf);
>  			if (tmp < 0)
> @@ -461,7 +463,8 @@ static int mmap_vmcore(struct file *file
>  		if (start < m->offset + m->size) {
>  			u64 paddr = 0;
>  
> -			tsz = min_t(size_t, m->offset + m->size - start, size);
> +			tsz = (size_t)min_t(unsigned long long,
> +					    m->offset + m->size - start, size);
>  			paddr = m->paddr + start - m->offset;
>  			if (vmcore_remap_oldmem_pfn(vma, vma->vm_start + len,
>  						    paddr >> PAGE_SHIFT, tsz,