[PATCH 2/2] [PATCH 2/2] proc-vmcore: wrong data type casting fix

[PATCH 2/2] [PATCH 2/2] proc-vmcore: wrong data type casting fix

[dyoung]

[-- Attachment #1: 0002-proc-vmcore-wrong-data-type-casting-fix.patch --]
[-- Type: text/plain, Size: 1668 bytes --]

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:
1) read_vmcore will refuse to continue so makedumpfile fails.
2) mmap_vmcore will trigger BUG_ON() in remap_pfn_range().

Use min_lt instead so that the variables are not truncated.

Signed-off-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Dave Young <dyoung@redhat.com>
---
 fs/proc/vmcore.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- linux.orig/fs/proc/vmcore.c
+++ linux/fs/proc/vmcore.c
@@ -231,7 +231,8 @@ 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_lt(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 +462,7 @@ 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_lt(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,

Re: [PATCH 2/2] [PATCH 2/2] proc-vmcore: wrong data type casting fix

[Minfei Huang]

On 03/11/16 at 02:21pm, dyoung@redhat.com wrote:
> @@ -231,7 +231,8 @@ 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_lt(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 +462,7 @@ 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_lt(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,

Hi, Dave.

Seems the previous parameter is unsigned long long, and the later one is
size_t. The size of both these types doesn't change in running time, why
not use min_t(unsigned long long, a, b) instead?

Thanks
Minfei

Re: [PATCH 2/2] [PATCH 2/2] proc-vmcore: wrong data type casting fix

[Dave Young]

Hi, Minfei

On 03/11/16 at 03:19pm, Minfei Huang wrote:
> On 03/11/16 at 02:21pm, dyoung@redhat.com wrote:
> > @@ -231,7 +231,8 @@ 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_lt(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 +462,7 @@ 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_lt(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,
> 
> Hi, Dave.
> 
> Seems the previous parameter is unsigned long long, and the later one is
> size_t. The size of both these types doesn't change in running time, why
> not use min_t(unsigned long long, a, b) instead?

Just want a common macro so it can benefit other users so that we can simply
use it without knowning type details and avoid such similar bugs also.

Thanks
Dave