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Subject[PATCH 4.7 32/45] vfs,mm: fix a dead loop in truncate_inode_pages_range()
4.7-stable review patch.  If anyone has any objections, please let me know.


From: Wei Fang <>

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.

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

Signed-off-by: Wei Fang <>
Cc: Christoph Hellwig <>
Cc: Dave Chinner <>
Cc: Al Viro <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Greg Kroah-Hartman <>

mm/filemap.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1609,6 +1609,10 @@ 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_SHIFT;
prev_index = ra->prev_pos >> PAGE_SHIFT;
prev_offset = ra->prev_pos & (PAGE_SIZE-1);

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