CVE-2021-47460

In the Linux kernel, the following vulnerability has been resolved: ocfs2:
fix data corruption after conversion from inline format Commit 6dbf7bb55598
(“fs: Don’t invalidate page buffers in block_write_full_page()”) uncovered
a latent bug in ocfs2 conversion from inline inode format to a normal inode
format. The code in ocfs2_convert_inline_data_to_extents() attempts to zero
out the whole cluster allocated for file data by grabbing, zeroing, and
dirtying all pages covering this cluster. However these pages are beyond
i_size, thus writeback code generally ignores these dirty pages and no
blocks were ever actually zeroed on the disk. This oversight was fixed by
commit 693c241a5f6a (“ocfs2: No need to zero pages past i_size.”) for
standard ocfs2 write path, inline conversion path was apparently forgotten;
the commit log also has a reasoning why the zeroing actually is not needed.
After commit 6dbf7bb55598, things became worse as writeback code stopped
invalidating buffers on pages beyond i_size and thus these pages end up
with clean PageDirty bit but with buffers attached to these pages being
still dirty. So when a file is converted from inline format, then writeback
triggers, and then the file is grown so that these pages become valid, the
invalid dirtiness state is preserved, mark_buffer_dirty() does nothing on
these pages (buffers are already dirty) but page is never written back
because it is clean. So data written to these pages is lost once pages are
reclaimed. Simple reproducer for the problem is: xfs_io -f -c “pwrite 0
2000” -c “pwrite 2000 2000” -c “fsync” \ -c “pwrite 4000 2000” ocfs2_file
After unmounting and mounting the fs again, you can observe that end of
‘ocfs2_file’ has lost its contents. Fix the problem by not doing the
pointless zeroing during conversion from inline format similarly as in the
standard write path. [[email protected]: fix whitespace, per
Joseph]