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authorWei Fang <fangwei1@huawei.com>2016-10-07 17:01:52 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-10-07 18:46:29 -0700
commitc2a9737f45e27d8263ff9643f994bda9bac0b944 (patch)
treefda4cf829320f7a3334c75e50308dfcb6daea0f3 /mm
parent14f099107aacea5ffa77d4fd3be52671e3925b93 (diff)
downloadlinux-c2a9737f45e27d8263ff9643f994bda9bac0b944.tar.bz2
vfs,mm: fix a dead loop in truncate_inode_pages_range()
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> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/filemap.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index 1b05f75aea0f..2f7b7783bd6b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1687,6 +1687,10 @@ 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);