[PATCH] xfs: truncate should remove all blocks, not just to the end of the page cache

["Darrick J. Wong" <darrick.wong@oracle.com>]

From: Darrick J. Wong <darrick.wong@oracle.com>

xfs_itruncate_extents_flags() is supposed to unmap every block in a file
from EOF onwards.  Oddly, it uses s_maxbytes as the upper limit to the
bunmapi range, even though s_maxbytes reflects the highest offset the
pagecache can support, not the highest offset that XFS supports.

The result of this confusion is that if you create a 20T file on a
64-bit machine, mount the filesystem on a 32-bit machine, and remove the
file, we leak everything above 16T.  Fix this by capping the bunmapi
request at the maximum possible block offset, not s_maxbytes.

Fixes: 32972383ca462 ("xfs: make largest supported offset less shouty")
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 fs/xfs/xfs_inode.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 401da197f012..eaa85d5933cb 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -1544,9 +1544,12 @@ xfs_itruncate_extents_flags(
 	 * possible file size.  If the first block to be removed is
 	 * beyond the maximum file size (ie it is the same as last_block),
 	 * then there is nothing to do.
+	 *
+	 * We have to free all the blocks to the bmbt maximum offset, even if
+	 * the page cache can't scale that far.
 	 */
 	first_unmap_block = XFS_B_TO_FSB(mp, (xfs_ufsize_t)new_size);
-	last_block = XFS_B_TO_FSB(mp, mp->m_super->s_maxbytes);
+	last_block = (1ULL << BMBT_STARTOFF_BITLEN) - 1;
 	if (first_unmap_block == last_block)
 		return 0;