Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1582000 > unrolled thread

[PATCH 3.16 105/306] vfs,mm: fix a dead loop in truncate_inode_pages_range()

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  [PATCH 3.16 105/306] vfs,mm: fix a dead loop in truncate_inode_pages_range() Ben Hutchings <ben@decadent.org.uk> - 2017-02-16 00:40 +0100
    Re: [PATCH 3.16 105/306] vfs,mm: fix a dead loop in  truncate_inode_pages_range() Wei Fang <fangwei1@huawei.com> - 2017-02-16 02:30 +0100
      Re: [PATCH 3.16 105/306] vfs,mm: fix a dead loop in  truncate_inode_pages_range() Ben Hutchings <ben@decadent.org.uk> - 2017-02-16 17:10 +0100

#1582000 — [PATCH 3.16 105/306] vfs,mm: fix a dead loop in truncate_inode_pages_range()

3.16.40-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Wei Fang <fangwei1@huawei.com>

commit c2a9737f45e27d8263ff9643f994bda9bac0b944 upstream.

We triggered a deadloop in truncate_inode_pages_range() on 32 bits
architecture with the test case bellow:

	...
	fd = open();
	write(fd, buf, 4096);
	preadv64(fd, &iovec, 1, 0xffffffff000);
	ftruncate(fd, 0);
	...

Then ftruncate() will not return forever.

The filesystem used in this case is ubifs, but it can be triggered on
many other filesystems.

When preadv64() is called with offset=0xffffffff000, a page with
index=0xffffffff will be added to the radix tree of ->mapping.  Then
this page can be found in ->mapping with pagevec_lookup().  After that,
truncate_inode_pages_range(), which is called in ftruncate(), will fall
into an infinite loop:

 - find a page with index=0xffffffff, since index>=end, this page won't
   be truncated

 - index++, and index become 0

 - the page with index=0xffffffff will be found again

The data type of index is unsigned long, so index won't overflow to 0 on
64 bits architecture in this case, and the dead loop won't happen.

Since truncate_inode_pages_range() is executed with holding lock of
inode->i_rwsem, any operation related with this lock will be blocked,
and a hung task will happen, e.g.:

  INFO: task truncate_test:3364 blocked for more than 120 seconds.
  ...
     call_rwsem_down_write_failed+0x17/0x30
     generic_file_write_iter+0x32/0x1c0
     ubifs_write_iter+0xcc/0x170
     __vfs_write+0xc4/0x120
     vfs_write+0xb2/0x1b0
     SyS_write+0x46/0xa0

The page with index=0xffffffff added to ->mapping is useless.  Fix this
by checking the read position before allocating pages.

Link: http://lkml.kernel.org/r/1475151010-40166-1-git-send-email-fangwei1@huawei.com
Signed-off-by: Wei Fang <fangwei1@huawei.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 mm/filemap.c | 4 ++++
 1 file changed, 4 insertions(+)

--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1464,6 +1464,10 @@ static ssize_t do_generic_file_read(stru
 	unsigned int prev_offset;
 	int error = 0;
 
+	if (unlikely(*ppos >= inode->i_sb->s_maxbytes))
+		return -EINVAL;
+	iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
+
 	index = *ppos >> PAGE_CACHE_SHIFT;
 	prev_index = ra->prev_pos >> PAGE_CACHE_SHIFT;
 	prev_offset = ra->prev_pos & (PAGE_CACHE_SIZE-1);

[toc] | [next] | [standalone]

#1582214 — Re: [PATCH 3.16 105/306] vfs,mm: fix a dead loop in truncate_inode_pages_range()

Hi, Ben,

Commit d05c5f7ba164 "vfs,mm: fix return value of read() at s_maxbytes"
need be backported with this patch, otherwise we'll get an error when
reading at the end of the file.

Thanks,
Wei

On 2017/2/16 6:41, Ben Hutchings wrote:
> 3.16.40-rc1 review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Wei Fang <fangwei1@huawei.com>
> 
> commit c2a9737f45e27d8263ff9643f994bda9bac0b944 upstream.
> 
> We triggered a deadloop in truncate_inode_pages_range() on 32 bits
> architecture with the test case bellow:
> 
> 	...
> 	fd = open();
> 	write(fd, buf, 4096);
> 	preadv64(fd, &iovec, 1, 0xffffffff000);
> 	ftruncate(fd, 0);
> 	...
> 
> Then ftruncate() will not return forever.
> 
> The filesystem used in this case is ubifs, but it can be triggered on
> many other filesystems.
> 
> When preadv64() is called with offset=0xffffffff000, a page with
> index=0xffffffff will be added to the radix tree of ->mapping.  Then
> this page can be found in ->mapping with pagevec_lookup().  After that,
> truncate_inode_pages_range(), which is called in ftruncate(), will fall
> into an infinite loop:
> 
>  - find a page with index=0xffffffff, since index>=end, this page won't
>    be truncated
> 
>  - index++, and index become 0
> 
>  - the page with index=0xffffffff will be found again
> 
> The data type of index is unsigned long, so index won't overflow to 0 on
> 64 bits architecture in this case, and the dead loop won't happen.
> 
> Since truncate_inode_pages_range() is executed with holding lock of
> inode->i_rwsem, any operation related with this lock will be blocked,
> and a hung task will happen, e.g.:
> 
>   INFO: task truncate_test:3364 blocked for more than 120 seconds.
>   ...
>      call_rwsem_down_write_failed+0x17/0x30
>      generic_file_write_iter+0x32/0x1c0
>      ubifs_write_iter+0xcc/0x170
>      __vfs_write+0xc4/0x120
>      vfs_write+0xb2/0x1b0
>      SyS_write+0x46/0xa0
> 
> The page with index=0xffffffff added to ->mapping is useless.  Fix this
> by checking the read position before allocating pages.
> 
> Link: http://lkml.kernel.org/r/1475151010-40166-1-git-send-email-fangwei1@huawei.com
> Signed-off-by: Wei Fang <fangwei1@huawei.com>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Dave Chinner <david@fromorbit.com>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> [bwh: Backported to 3.16: adjust context]
> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
> ---
>  mm/filemap.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1464,6 +1464,10 @@ static ssize_t do_generic_file_read(stru
>  	unsigned int prev_offset;
>  	int error = 0;
>  
> +	if (unlikely(*ppos >= inode->i_sb->s_maxbytes))
> +		return -EINVAL;
> +	iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
> +
>  	index = *ppos >> PAGE_CACHE_SHIFT;
>  	prev_index = ra->prev_pos >> PAGE_CACHE_SHIFT;
>  	prev_offset = ra->prev_pos & (PAGE_CACHE_SIZE-1);
> 

[toc] | [prev] | [next] | [standalone]

#1582668 — Re: [PATCH 3.16 105/306] vfs,mm: fix a dead loop in truncate_inode_pages_range()

[Multipart message — attachments visible in raw view] — view raw

On Thu, 2017-02-16 at 09:25 +0800, Wei Fang wrote:
> Hi, Ben,
> 
> Commit d05c5f7ba164 "vfs,mm: fix return value of read() at s_maxbytes"
> need be backported with this patch, otherwise we'll get an error when
> reading at the end of the file.
[...]

Sorry, I should have seen the notes for this commit pointing that out. 
I'll add the second commit.

Ben.

-- 
Ben Hutchings
The most exhausting thing in life is being insincere. - Anne Morrow
Lindberg

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web