Re: [PATCH] Btrfs: fix out of bounds array access while reading extent buffer

[kbuild test robot]

Hi Liu,

[auto build test WARNING on v4.13-rc4]
[also build test WARNING on next-20170811]
[cannot apply to btrfs/next]
[if your patch is applied to the wrong git tree, please drop us a note to help 
improve the system]

url:
https://github.com/0day-ci/linux/commits/Liu-Bo/Btrfs-fix-out-of-bounds-array-access-while-reading-extent-buffer/20170810-235607
config: x86_64-randconfig-a0-08120433 (attached as .config)
compiler: gcc-4.4 (Debian 4.4.7-8) 4.4.7
reproduce:
# save the attached .config to linux build tree
make ARCH=x86_64 

All warnings (new ones prefixed by >>):

   fs//btrfs/extent_io.c: In function 'read_extent_buffer':
>> fs//btrfs/extent_io.c:5419: warning: unused variable 'num_pages'

vim +/num_pages +5419 fs//btrfs/extent_io.c

  5407  
  5408  void read_extent_buffer(struct extent_buffer *eb, void *dstv,
  5409  unsigned long start,
  5410  unsigned long len)
  5411  {
  5412  size_t cur;
  5413  size_t offset;
  5414  struct page *page;
  5415  char *kaddr;
  5416  char *dst = (char *)dstv;
  5417  size_t start_offset = eb->start & ((u64)PAGE_SIZE - 1);
  5418  unsigned long i = (start_offset + start) >> PAGE_SHIFT;
> 5419  unsigned long num_pages = num_extent_pages(eb->start, eb->len);
  5420  
  5421  if (start + len > eb->len) {
  5422  WARN(1, KERN_ERR "btrfs bad mapping eb start %llu len 
%lu, wanted %lu %lu\n",
  5423   eb->start, eb->len, start, len);
  5424  memset(dst, 0, len);
  5425  return;
  5426  }
  5427  
  5428  offset = (start_offset + start) & (PAGE_SIZE - 1);
  5429  
  5430  while (len > 0) {
  5431  ASSERT(i < num_pages);
  5432  page = eb->pages[i];
  5433  
  5434  cur = min(len, (PAGE_SIZE - offset));
  5435  kaddr = page_address(page);
  5436  memcpy(dst, kaddr + offset, cur);
  5437  
  5438  dst += cur;
  5439  len -= cur;
  5440  offset = 0;
  5441  i++;
  5442  }
  5443  }
  5444  

---
0-DAY kernel test infrastructureOpen Source Technology Center
https://lists.01.org/pipermail/kbuild-all   Intel Corporation


.config.gz
Description: application/gzip

Re: [PATCH] Btrfs: fix out of bounds array access while reading extent buffer

[Filipe Manana]

On Tue, Aug 8, 2017 at 6:05 PM, Liu Bo  wrote:
> Hi Filipe,
>
> On Tue, Aug 08, 2017 at 09:47:21AM +0100, Filipe Manana wrote:
>> On Mon, Aug 7, 2017 at 8:39 PM, Liu Bo  wrote:
>> > There is a cornel case that slip through the checkers in functions
>> > reading extent buffer, ie.
>> >
>> > if (start < eb->len) and (start + len > eb->len),
>> > then
>> >
>> > a) map_private_extent_buffer() returns immediately because
>> > it's thinking the range spans across two pages,
>> >
>> > b) and the checkers in read_extent_buffer(), WARN_ON(start > eb->len)
>> > and WARN_ON(start + len > eb->start + eb->len), both are OK in this
>> > corner case, but it'd actually try to access the eb->pages out of
>> > bounds because of (start + len > eb->len).
>> >
>> > The case is found by switching extent inline ref type from shared data
>> > ref to non-shared data ref.
>> >
>> > This is adding proper checks in order to avoid invalid memory access,
>> > ie. 'general protection', before it's too late.
>>
>> Hi Bo,
>>
>> I don't understand these 2 last paragraphs.
>> How do you fix the invalid memory access? All the change does is make
>> sure that attempts to read from invalid regions of an extent buffer
>> result in a warning and returning an error code. Those paragraphs give
>> the idea that the problem is that some caller is passing a wrong
>> offset/length pair, however you aren't fixing any caller. can you
>> clarify?
>>
>
> I see your doubt, that wrong offset/length pair comes from one of
> btrfs_setget helpers, eg. btrfs_extent_data_ref_root.
>
> The invalid memory access happens when the pointer it's using to
> access fields in "struct btrfs_extent_data_ref" is actually a "struct
> btrfs_shared_data_ref", this is caused by switching those types.
>
> So the offset/length pair is correct from btrfs_setget helper's point
> of view, but it's just using the wrong helper due to a wrong ref type
> (in v2 this'll be added to the commit log to clarity).
>
>> Also when you say " The case is found by switching extent inline ref
>> type from shared data ref to non-shared data ref", it gives the idea
>> this is a deterministic problem that always happens when doing that
>> switch. If so, can we have a test case?
>>
>
> It is deterministic, but it depends on patching btrfs-corrupt-block
> and last time I posted a corrupt-block related case, I was told that
> tool is gonna change a lot and maybe get deleted in the near future,
> so it's not yet suitable for fstests cases.

Ok, so this only happens if the metadata is corrupted. It wasn't clear
for me from the change log.

Thanks.

>
>> Also missing the word "fault" after 'general protection'.
>>
>
> Yeah, there is a 'fault', the full text is
> "general protection fault:  [#1] SMP KASAN",
> will update.
>
> Thanks,
>
> -liubo
>
>> Thanks.
>>
>> >
>> > Signed-off-by: Liu Bo 
>> > ---
>> >  fs/btrfs/extent_io.c | 22 ++
>> >  1 file changed, 14 insertions(+), 8 deletions(-)
>> >
>> > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
>> > index 0aff9b2..d198e87 100644
>> > --- a/fs/btrfs/extent_io.c
>> > +++ b/fs/btrfs/extent_io.c
>> > @@ -5416,13 +5416,19 @@ void read_extent_buffer(struct extent_buffer *eb, 
>> > void *dstv,
>> > char *dst = (char *)dstv;
>> > size_t start_offset = eb->start & ((u64)PAGE_SIZE - 1);
>> > unsigned long i = (start_offset + start) >> PAGE_SHIFT;
>> > +   unsigned long num_pages = num_extent_pages(eb->start, eb->len);
>> >
>> > -   WARN_ON(start > eb->len);
>> > -   WARN_ON(start + len > eb->start + eb->len);
>> > +   if (start + len > eb->len) {
>> > +   WARN(1, KERN_ERR "btrfs bad mapping eb start %llu len %lu, 
>> > wanted %lu %lu\n",
>> > +eb->start, eb->len, start, len);
>> > +   memset(dst, 0, len);
>> > +   return;
>> > +   }
>> >
>> > offset = (start_offset + start) & (PAGE_SIZE - 1);
>> >
>> > while (len > 0) {
>> > +   ASSERT(i < num_pages);
>> > page = eb->pages[i];
>> >
>> > cur = min(len, (PAGE_SIZE - offset));
>> > @@ -5491,6 +5497,12 @@ int map_private_extent_buffer(struct extent_buffer 
>> > *eb, unsigned long start,
>> > unsigned long end_i = (start_offset + start + min_len - 1) >>
>> > PAGE_SHIFT;
>> >
>> > +   if (start + min_len > eb->len) {
>> > +   WARN(1, KERN_ERR "btrfs bad mapping eb start %llu len %lu, 
>> > wanted %lu %lu\n",
>> > +  eb->start, eb->len, start, min_len);
>> > +   return -EINVAL;
>> > +   }
>> > +
>> > if (i != end_i)
>> > return 1;
>> >
>> > @@ -5502,12 +5514,6 @@ int map_private_extent_buffer(struct extent_buffer 
>> > *eb, unsigned long start,
>> > *map_start = ((u64)i << PAGE_SHIFT) - start_offset;
>> > }
>> >
>> > -   if (start + min_len > 

Re: [PATCH] Btrfs: fix out of bounds array access while reading extent buffer

[Liu Bo]

Hi Filipe,

On Tue, Aug 08, 2017 at 09:47:21AM +0100, Filipe Manana wrote:
> On Mon, Aug 7, 2017 at 8:39 PM, Liu Bo  wrote:
> > There is a cornel case that slip through the checkers in functions
> > reading extent buffer, ie.
> >
> > if (start < eb->len) and (start + len > eb->len),
> > then
> >
> > a) map_private_extent_buffer() returns immediately because
> > it's thinking the range spans across two pages,
> >
> > b) and the checkers in read_extent_buffer(), WARN_ON(start > eb->len)
> > and WARN_ON(start + len > eb->start + eb->len), both are OK in this
> > corner case, but it'd actually try to access the eb->pages out of
> > bounds because of (start + len > eb->len).
> >
> > The case is found by switching extent inline ref type from shared data
> > ref to non-shared data ref.
> >
> > This is adding proper checks in order to avoid invalid memory access,
> > ie. 'general protection', before it's too late.
> 
> Hi Bo,
> 
> I don't understand these 2 last paragraphs.
> How do you fix the invalid memory access? All the change does is make
> sure that attempts to read from invalid regions of an extent buffer
> result in a warning and returning an error code. Those paragraphs give
> the idea that the problem is that some caller is passing a wrong
> offset/length pair, however you aren't fixing any caller. can you
> clarify?
>

I see your doubt, that wrong offset/length pair comes from one of
btrfs_setget helpers, eg. btrfs_extent_data_ref_root.

The invalid memory access happens when the pointer it's using to
access fields in "struct btrfs_extent_data_ref" is actually a "struct
btrfs_shared_data_ref", this is caused by switching those types.

So the offset/length pair is correct from btrfs_setget helper's point
of view, but it's just using the wrong helper due to a wrong ref type
(in v2 this'll be added to the commit log to clarity).

> Also when you say " The case is found by switching extent inline ref
> type from shared data ref to non-shared data ref", it gives the idea
> this is a deterministic problem that always happens when doing that
> switch. If so, can we have a test case?
>

It is deterministic, but it depends on patching btrfs-corrupt-block
and last time I posted a corrupt-block related case, I was told that
tool is gonna change a lot and maybe get deleted in the near future,
so it's not yet suitable for fstests cases.

> Also missing the word "fault" after 'general protection'.
>

Yeah, there is a 'fault', the full text is
"general protection fault:  [#1] SMP KASAN",
will update.

Thanks,

-liubo

> Thanks.
> 
> >
> > Signed-off-by: Liu Bo 
> > ---
> >  fs/btrfs/extent_io.c | 22 ++
> >  1 file changed, 14 insertions(+), 8 deletions(-)
> >
> > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> > index 0aff9b2..d198e87 100644
> > --- a/fs/btrfs/extent_io.c
> > +++ b/fs/btrfs/extent_io.c
> > @@ -5416,13 +5416,19 @@ void read_extent_buffer(struct extent_buffer *eb, 
> > void *dstv,
> > char *dst = (char *)dstv;
> > size_t start_offset = eb->start & ((u64)PAGE_SIZE - 1);
> > unsigned long i = (start_offset + start) >> PAGE_SHIFT;
> > +   unsigned long num_pages = num_extent_pages(eb->start, eb->len);
> >
> > -   WARN_ON(start > eb->len);
> > -   WARN_ON(start + len > eb->start + eb->len);
> > +   if (start + len > eb->len) {
> > +   WARN(1, KERN_ERR "btrfs bad mapping eb start %llu len %lu, 
> > wanted %lu %lu\n",
> > +eb->start, eb->len, start, len);
> > +   memset(dst, 0, len);
> > +   return;
> > +   }
> >
> > offset = (start_offset + start) & (PAGE_SIZE - 1);
> >
> > while (len > 0) {
> > +   ASSERT(i < num_pages);
> > page = eb->pages[i];
> >
> > cur = min(len, (PAGE_SIZE - offset));
> > @@ -5491,6 +5497,12 @@ int map_private_extent_buffer(struct extent_buffer 
> > *eb, unsigned long start,
> > unsigned long end_i = (start_offset + start + min_len - 1) >>
> > PAGE_SHIFT;
> >
> > +   if (start + min_len > eb->len) {
> > +   WARN(1, KERN_ERR "btrfs bad mapping eb start %llu len %lu, 
> > wanted %lu %lu\n",
> > +  eb->start, eb->len, start, min_len);
> > +   return -EINVAL;
> > +   }
> > +
> > if (i != end_i)
> > return 1;
> >
> > @@ -5502,12 +5514,6 @@ int map_private_extent_buffer(struct extent_buffer 
> > *eb, unsigned long start,
> > *map_start = ((u64)i << PAGE_SHIFT) - start_offset;
> > }
> >
> > -   if (start + min_len > eb->len) {
> > -   WARN(1, KERN_ERR "btrfs bad mapping eb start %llu len %lu, 
> > wanted %lu %lu\n",
> > -  eb->start, eb->len, start, min_len);
> > -   return -EINVAL;
> > -   }
> > -
> > p = eb->pages[i];
> > kaddr = page_address(p);
> > *map = 

Re: [PATCH] Btrfs: fix out of bounds array access while reading extent buffer

[Filipe Manana]

On Mon, Aug 7, 2017 at 8:39 PM, Liu Bo  wrote:
> There is a cornel case that slip through the checkers in functions
> reading extent buffer, ie.
>
> if (start < eb->len) and (start + len > eb->len),
> then
>
> a) map_private_extent_buffer() returns immediately because
> it's thinking the range spans across two pages,
>
> b) and the checkers in read_extent_buffer(), WARN_ON(start > eb->len)
> and WARN_ON(start + len > eb->start + eb->len), both are OK in this
> corner case, but it'd actually try to access the eb->pages out of
> bounds because of (start + len > eb->len).
>
> The case is found by switching extent inline ref type from shared data
> ref to non-shared data ref.
>
> This is adding proper checks in order to avoid invalid memory access,
> ie. 'general protection', before it's too late.

Hi Bo,

I don't understand these 2 last paragraphs.
How do you fix the invalid memory access? All the change does is make
sure that attempts to read from invalid regions of an extent buffer
result in a warning and returning an error code. Those paragraphs give
the idea that the problem is that some caller is passing a wrong
offset/length pair, however you aren't fixing any caller. can you
clarify?

Also when you say " The case is found by switching extent inline ref
type from shared data ref to non-shared data ref", it gives the idea
this is a deterministic problem that always happens when doing that
switch. If so, can we have a test case?

Also missing the word "fault" after 'general protection'.

Thanks.

>
> Signed-off-by: Liu Bo 
> ---
>  fs/btrfs/extent_io.c | 22 ++
>  1 file changed, 14 insertions(+), 8 deletions(-)
>
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index 0aff9b2..d198e87 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -5416,13 +5416,19 @@ void read_extent_buffer(struct extent_buffer *eb, 
> void *dstv,
> char *dst = (char *)dstv;
> size_t start_offset = eb->start & ((u64)PAGE_SIZE - 1);
> unsigned long i = (start_offset + start) >> PAGE_SHIFT;
> +   unsigned long num_pages = num_extent_pages(eb->start, eb->len);
>
> -   WARN_ON(start > eb->len);
> -   WARN_ON(start + len > eb->start + eb->len);
> +   if (start + len > eb->len) {
> +   WARN(1, KERN_ERR "btrfs bad mapping eb start %llu len %lu, 
> wanted %lu %lu\n",
> +eb->start, eb->len, start, len);
> +   memset(dst, 0, len);
> +   return;
> +   }
>
> offset = (start_offset + start) & (PAGE_SIZE - 1);
>
> while (len > 0) {
> +   ASSERT(i < num_pages);
> page = eb->pages[i];
>
> cur = min(len, (PAGE_SIZE - offset));
> @@ -5491,6 +5497,12 @@ int map_private_extent_buffer(struct extent_buffer 
> *eb, unsigned long start,
> unsigned long end_i = (start_offset + start + min_len - 1) >>
> PAGE_SHIFT;
>
> +   if (start + min_len > eb->len) {
> +   WARN(1, KERN_ERR "btrfs bad mapping eb start %llu len %lu, 
> wanted %lu %lu\n",
> +  eb->start, eb->len, start, min_len);
> +   return -EINVAL;
> +   }
> +
> if (i != end_i)
> return 1;
>
> @@ -5502,12 +5514,6 @@ int map_private_extent_buffer(struct extent_buffer 
> *eb, unsigned long start,
> *map_start = ((u64)i << PAGE_SHIFT) - start_offset;
> }
>
> -   if (start + min_len > eb->len) {
> -   WARN(1, KERN_ERR "btrfs bad mapping eb start %llu len %lu, 
> wanted %lu %lu\n",
> -  eb->start, eb->len, start, min_len);
> -   return -EINVAL;
> -   }
> -
> p = eb->pages[i];
> kaddr = page_address(p);
> *map = kaddr + offset;
> --
> 2.9.4
>
> --
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-- 
Filipe David Manana,

“Whether you think you can, or you think you can't — you're right.”
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