[Focal, Bionic] xfs: map unwritten blocks in XFS_IOC_{ALLOC, FREE}SP just like fallocate

[Thadeu Lima de Souza Cascardo]

From: "Darrick J. Wong" <djwong at kernel.org>

The old ALLOCSP/FREESP ioctls in XFS can be used to preallocate space at
the end of files, just like fallocate and RESVSP.  Make the behavior
consistent with the other ioctls.

Reported-by: Kirill Tkhai <ktkhai at virtuozzo.com>
Signed-off-by: Darrick J. Wong <djwong at kernel.org>
Signed-off-by: Darrick J. Wong <darrick.wong at oracle.com>
Reviewed-by: Dave Chinner <dchinner at redhat.com>
Reviewed-by: Eric Sandeen <sandeen at redhat.com>
(backported from commit 983d8e60f50806f90534cc5373d0ce867e5aaf79)
[cascardo: always use XFS_BMAPI_PREALLOC on xfs_alloc_file_space]
CVE-2021-4155
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
---
 fs/xfs/xfs_ioctl.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 2409b4ff4e07..6d3abb84451c 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -714,7 +714,8 @@ xfs_ioc_space(
 		flags |= XFS_PREALLOC_CLEAR;
 		if (bf->l_start > XFS_ISIZE(ip)) {
 			error = xfs_alloc_file_space(ip, XFS_ISIZE(ip),
-					bf->l_start - XFS_ISIZE(ip), 0);
+					bf->l_start - XFS_ISIZE(ip),
+					XFS_BMAPI_PREALLOC);
 			if (error)
 				goto out_unlock;
 		}
-- 
2.32.0