On 03/14/16 at 12:25pm, HATAYAMA Daisuke wrote:
> From: Dave Young <dyoung at redhat.com>
> Subject: [PATCH V2] proc-vmcore: wrong data type casting fix
> Date: Fri, 11 Mar 2016 16:42:48 +0800
>
> > 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
>
> That is, size_t and loff_t are defined as follows on i686:
>
> (gdb) ptype size_t
> type = unsigned int
> (gdb) ptype loff_t
> type = long long int
>
> So casting by size_t means truncating a given value by 4GB.
>
> Then, if (m->offset + m->size - *fpos) is equal to or larger than 4GB,
> and is aligned with 4GB, the resulted value is 0, and
Truncating doesn't mean align. If (m->offset + m->size - *fpos) is
larger than 4G, E.g 0x10000000f, the truncating result will be 0xf.
>
> > we will get tsz = 0. It is of course not an expected result.
We won't always get "tsz=0", just get the lower 32 bit value.
> >
> > 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().
> >
>
> we reach these errors.
>
> If (m->offset + m->size - *fpos) is not aligned with 4GB,
> read_vmcore() or mmap_vmcore() is performed with the truncated
> non-zero value as size (of course, this is also not expected value but
> the execution doesn't result in error). Then, fpos proceeds so that
> (m->offset + m->size - *fpos) is aligned with 4GB in the next loop,
> and we after all reach the errors.
>
> I think your patch description needs a bit more detail.
>
> It seems good to me that the patch itself.
>
> > 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>
> > ---
> > v1->v2: spelling fix in patch log
> > 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,
> >
> --
> Thanks.
> HATAYAMA, Daisuke
