Hi, Andrew
On 03/11/16 at 12:27pm, Andrew Morton wrote:
> On Fri, 11 Mar 2016 16:42:48 +0800 Dave Young <dyoung at 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 at redhat.com>
> > Signed-off-by: Dave Young <dyoung at 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.
>
>
> > 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
