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authorBrian Foster <bfoster@redhat.com>2020-10-30 00:30:48 +0300
committerDarrick J. Wong <darrick.wong@oracle.com>2020-11-04 19:52:46 +0300
commit869ae85dae64b5540e4362d7fe4cd520e10ec05c (patch)
treebb6969102f0b8a7cef7009964524e98532018f4d /fs/xfs/xfs_iops.c
parent2c334e12f957cd8c6bb66b4aa3f79848b7c33cab (diff)
downloadlinux-869ae85dae64b5540e4362d7fe4cd520e10ec05c.tar.xz
xfs: flush new eof page on truncate to avoid post-eof corruption
It is possible to expose non-zeroed post-EOF data in XFS if the new EOF page is dirty, backed by an unwritten block and the truncate happens to race with writeback. iomap_truncate_page() will not zero the post-EOF portion of the page if the underlying block is unwritten. The subsequent call to truncate_setsize() will, but doesn't dirty the page. Therefore, if writeback happens to complete after iomap_truncate_page() (so it still sees the unwritten block) but before truncate_setsize(), the cached page becomes inconsistent with the on-disk block. A mapped read after the associated page is reclaimed or invalidated exposes non-zero post-EOF data. For example, consider the following sequence when run on a kernel modified to explicitly flush the new EOF page within the race window: $ xfs_io -fc "falloc 0 4k" -c fsync /mnt/file $ xfs_io -c "pwrite 0 4k" -c "truncate 1k" /mnt/file ... $ xfs_io -c "mmap 0 4k" -c "mread -v 1k 8" /mnt/file 00000400: 00 00 00 00 00 00 00 00 ........ $ umount /mnt/; mount <dev> /mnt/ $ xfs_io -c "mmap 0 4k" -c "mread -v 1k 8" /mnt/file 00000400: cd cd cd cd cd cd cd cd ........ Update xfs_setattr_size() to explicitly flush the new EOF page prior to the page truncate to ensure iomap has the latest state of the underlying block. Fixes: 68a9f5e7007c ("xfs: implement iomap based buffered write path") Signed-off-by: Brian Foster <bfoster@redhat.com> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Diffstat (limited to 'fs/xfs/xfs_iops.c')
-rw-r--r--fs/xfs/xfs_iops.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 5e165456da68..1414ab79eacf 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -911,6 +911,16 @@ xfs_setattr_size(
error = iomap_zero_range(inode, oldsize, newsize - oldsize,
&did_zeroing, &xfs_buffered_write_iomap_ops);
} else {
+ /*
+ * iomap won't detect a dirty page over an unwritten block (or a
+ * cow block over a hole) and subsequently skips zeroing the
+ * newly post-EOF portion of the page. Flush the new EOF to
+ * convert the block before the pagecache truncate.
+ */
+ error = filemap_write_and_wait_range(inode->i_mapping, newsize,
+ newsize);
+ if (error)
+ return error;
error = iomap_truncate_page(inode, newsize, &did_zeroing,
&xfs_buffered_write_iomap_ops);
}