xfs: add capability check to free eofblocks ioctl

commit 8c567a7fab6e086a0284eee2db82348521e7120c upstream.

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@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Gao feng <gaofeng@cn.fujitsu.com>
Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
Cc: Kees Cook <keescook@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 5e999680094a..ca01d830e989 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1612,6 +1612,12 @@ xfs_file_ioctl(
         case XFS_IOC_FREE_EOFBLOCKS: {
                 struct xfs_eofblocks eofb;
 
+                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);