* [RFC][PATCH] vfs,mm: fix a dead loop in truncate_inode_pages_range()
@ 2016-09-29 12:10 Wei Fang
2016-09-29 13:43 ` Christoph Hellwig
0 siblings, 1 reply; 4+ messages in thread
From: Wei Fang @ 2016-09-29 12:10 UTC (permalink / raw)
To: viro, akpm; +Cc: linux-mm, linux-fsdevel, Wei Fang, stable
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.
...
[<c03c2c44>] call_rwsem_down_write_failed+0x17/0x30
[<c00b93bc>] generic_file_write_iter+0x32/0x1c0
[<c01b7078>] ubifs_write_iter+0xcc/0x170
[<c00fae48>] __vfs_write+0xc4/0x120
[<c00fb784>] vfs_write+0xb2/0x1b0
[<c00fbbe4>] SyS_write+0x46/0xa0
The page with index=0xffffffff added to ->mapping is useless.
Fix this by checking the read position before allocating pages.
Cc: stable@vger.kernel.org
Signed-off-by: Wei Fang <fangwei1@huawei.com>
---
mm/filemap.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/mm/filemap.c b/mm/filemap.c
index 1345f09..6946346 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1674,6 +1674,10 @@ static ssize_t do_generic_file_read(struct file *filp, loff_t *ppos,
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_SHIFT;
prev_index = ra->prev_pos >> PAGE_SHIFT;
prev_offset = ra->prev_pos & (PAGE_SIZE-1);
--
1.9.3
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^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [RFC][PATCH] vfs,mm: fix a dead loop in truncate_inode_pages_range()
2016-09-29 12:10 [RFC][PATCH] vfs,mm: fix a dead loop in truncate_inode_pages_range() Wei Fang
@ 2016-09-29 13:43 ` Christoph Hellwig
2016-09-30 0:54 ` Wei Fang
2016-09-30 1:02 ` Dave Chinner
0 siblings, 2 replies; 4+ messages in thread
From: Christoph Hellwig @ 2016-09-29 13:43 UTC (permalink / raw)
To: Wei Fang; +Cc: viro, akpm, linux-mm, linux-fsdevel, stable
Can you please add a testcase for this to xfstests?
Thanks!
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [RFC][PATCH] vfs,mm: fix a dead loop in truncate_inode_pages_range()
2016-09-29 13:43 ` Christoph Hellwig
@ 2016-09-30 0:54 ` Wei Fang
2016-09-30 1:02 ` Dave Chinner
1 sibling, 0 replies; 4+ messages in thread
From: Wei Fang @ 2016-09-30 0:54 UTC (permalink / raw)
To: Christoph Hellwig; +Cc: viro, akpm, linux-mm, linux-fsdevel, stable
OK, I'll do this.
Thanks,
Wei
On 2016/9/29 21:43, Christoph Hellwig wrote:
> Can you please add a testcase for this to xfstests?
>
> Thanks!
>
> .
>
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [RFC][PATCH] vfs,mm: fix a dead loop in truncate_inode_pages_range()
2016-09-29 13:43 ` Christoph Hellwig
2016-09-30 0:54 ` Wei Fang
@ 2016-09-30 1:02 ` Dave Chinner
1 sibling, 0 replies; 4+ messages in thread
From: Dave Chinner @ 2016-09-30 1:02 UTC (permalink / raw)
To: Christoph Hellwig; +Cc: Wei Fang, viro, akpm, linux-mm, linux-fsdevel, stable
On Thu, Sep 29, 2016 at 06:43:57AM -0700, Christoph Hellwig wrote:
> Can you please add a testcase for this to xfstests?
Seems like a copy of tests/xfs/071 (exercises read/write at the
highest page of the page cache) with an added ftruncate as a
generic tests would be a good start?
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
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^ permalink raw reply [flat|nested] 4+ messages in thread
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2016-09-29 12:10 [RFC][PATCH] vfs,mm: fix a dead loop in truncate_inode_pages_range() Wei Fang
2016-09-29 13:43 ` Christoph Hellwig
2016-09-30 0:54 ` Wei Fang
2016-09-30 1:02 ` Dave Chinner
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