From: Baoquan He <bhe@redhat.com>
To: xlpang@redhat.com
Cc: Dave Young <dyoung@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, d.hatayama@jp.fujitsu.com,
vgoyal@redhat.com, kexec@lists.infradead.org, nasa4836@gmail.com,
mhuang@redhat.com
Subject: Re: [PATCH V2] proc-vmcore: wrong data type casting fix
Date: Sat, 12 Mar 2016 21:59:32 +0800 [thread overview]
Message-ID: <20160312135932.GA3649@x1.redhat.com> (raw)
In-Reply-To: <56E40EF7.1050000@redhat.com>
On 03/12/16 at 08:43pm, Xunlei Pang wrote:
> On 2016/03/12 at 12:49, Dave Young wrote:
> > Hi, Andrew
> >
> > On 03/11/16 at 12:27pm, Andrew Morton wrote:
> >> On Fri, 11 Mar 2016 16:42:48 +0800 Dave Young <dyoung@redhat.com> wrote:
> >>
> >>> On i686 PAE enabled machine the contiguous physical area could be large
> >>> and it can cause trimming 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.
> >> I don't really understand this.
> >>
> >> vmcore.offset if loff_t which is 64-bit
> >> vmcore.size is long long
> >> *fpos is loff_t
> >>
> >> so the expression should all be done with 64-bit arithmetic anyway.
> > #define min_t(type, x, y) ({ \
> > type __min1 = (x); \
> > type __min2 = (y); \
> > __min1 < __min2 ? __min1: __min2; })
> >
> > Here x = m->offset + m->size - *fpos; the expression is done with 64bit
> > arithmetic, it is true. But x will be cast to size_t then compare x with y
> > The casting will cause problem.
> >
> >> Maybe buflen (size_t) has the wrong type, but the result of the other
> >> expression should be in-range by the time we come to doing the
> >> comparison.
> >>
> >>> During our tests there are two problems caused by it:
> >>> 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@redhat.com>
> >>> Signed-off-by: Dave Young <dyoung@redhat.com>
> >> I think we'll need a cc:stable here.
> > Agreed. Do you think I need repost for this?
> >
> >>> --- 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);
> >> This is rather a mess. Can we please try to fix this bug by choosing
> >> appropriate types rather than all the typecasting?
> > file read/mmap buflen is size_t, so tsz is alwyas less then buflen unless
> > m->offset + m->size - *fpos < buflen. The only problem is we need avoid large
> > value of m->offset + m->size - *fpos being casted thus it will mistakenly be
> > less than buflen.
>
> *
> Can we use "tsz = min(m->offset + m->size - *fpos, buflen)" instead?
> I think it's ok for this case (both have positive values), nothing will go wrong,
> also can make the code cleaner.
We can't. Macro min() has a type checking. min_t is necessary here.
>
> *
> >>
> >>> 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,
> > Thanks
> > Dave
>
next prev parent reply other threads:[~2016-03-12 13:59 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-11 8:42 [PATCH V2] proc-vmcore: wrong data type casting fix Dave Young
2016-03-11 20:27 ` Andrew Morton
2016-03-12 4:49 ` Dave Young
2016-03-12 12:43 ` Xunlei Pang
2016-03-12 13:59 ` Baoquan He [this message]
2016-03-13 6:11 ` Xunlei Pang
2016-03-14 2:41 ` Baoquan He
2016-03-14 3:25 ` HATAYAMA Daisuke
2016-03-14 3:31 ` Dave Young
2016-03-14 3:47 ` Baoquan He
2016-03-14 3:50 ` Baoquan He
2016-03-14 4:36 ` HATAYAMA Daisuke
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