[PATCH v8 6/7] xfs: add capability check to free eofblocks ioctl

[Dwight Engen]

Check for CAP_SYS_ADMIN since the caller can truncate preallocated
blocks from files they do not own nor have write access to. A more
fine grained access check was considered: require the caller to
specify their own uid/gid and to use inode_permission to check for
write, but this would not catch the case of an inode not reachable
via path traversal from the callers mount namespace.

Add check for read-only filesystem to free eofblocks ioctl.

Reviewed-by: Brian Foster <bfoster at redhat.com>
Reviewed-by: Dave Chinner <dchinner at redhat.com>
Reviewed-by: Gao feng <gaofeng at cn.fujitsu.com>
Signed-off-by: Dwight Engen <dwight.engen at oracle.com>
---
 fs/xfs/xfs_ioctl.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 20b4c7a..bdebc21 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1723,6 +1723,12 @@ xfs_file_ioctl(
 		struct xfs_fs_eofblocks eofb;
 		struct xfs_eofblocks keofb;
 
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+
+		if (mp->m_flags & XFS_MOUNT_RDONLY)
+			return -XFS_ERROR(EROFS);
+
 		if (copy_from_user(&eofb, arg, sizeof(eofb)))
 			return -XFS_ERROR(EFAULT);
 
-- 
1.8.1.4