[PATCH v7 6/7] xfs: add capable check to free eofblocks ioctl

[Dwight Engen <dwight.engen@xxxxxxxxxx>]

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.

Signed-off-by: Dwight Engen <dwight.engen@xxxxxxxxxx>
---
 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 6e72eff..b1990ac 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1613,6 +1613,12 @@ xfs_file_ioctl(
                struct xfs_fs_eofblocks eofb;
                struct xfs_eofblocks keofb;
 
+               if (!capable(CAP_SYS_ADMIN))
+                       return -EPERM;
+
+               if (IS_RDONLY(inode))
+                       return -XFS_ERROR(EROFS);
+
                if (copy_from_user(&eofb, arg, sizeof(eofb)))
                        return -XFS_ERROR(EFAULT);
 
-- 
1.8.1.4