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.
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.
> --- 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?
> 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,
