From: Wei Fang <fangwei1@xxxxxxxxxx> Subject: 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. ... [<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. Link: http://lkml.kernel.org/r/1475151010-40166-1-git-send-email-fangwei1@xxxxxxxxxx Signed-off-by: Wei Fang <fangwei1@xxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> Cc: Dave Chinner <david@xxxxxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/filemap.c | 4 ++++ 1 file changed, 4 insertions(+) diff -puN mm/filemap.c~vfsmm-fix-a-dead-loop-in-truncate_inode_pages_range mm/filemap.c --- a/mm/filemap.c~vfsmm-fix-a-dead-loop-in-truncate_inode_pages_range +++ a/mm/filemap.c @@ -1687,6 +1687,10 @@ 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); _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
