From 5a73e0ca54c77e067c3b12ea6f35e3e8681e8cf8 Mon Sep 17 00:00:00 2001
 From: Bram Moolenaar <Bram@vim.org>
 Date: Sat, 4 Nov 2017 21:35:01 +0100
 Subject: [PATCH] patch 8.0.1263: others can read the swap file if a user is
  careless
 
 Problem:    Others can read the swap file if a user is careless with his
             primary group.
 Solution:   If the group permission allows for reading but the world
             permissions doesn't, make sure the group is right.
 ---
  src/Makefile              |   1 +
  src/fileio.c              |  24 +++++++++-
  src/testdir/test_swap.vim | 112 ++++++++++++++++++++++++++++++----------------
  src/version.c             |   2 +
  4 files changed, 99 insertions(+), 40 deletions(-)
 
 diff --git a/src/fileio.c b/src/fileio.c
 index 87b85cf..34dcdb6 100644
 --- a/src/fileio.c
 +++ b/src/fileio.c
 @@ -716,7 +716,29 @@ readfile(
  	/* Set swap file protection bits after creating it. */
  	if (swap_mode > 0 && curbuf->b_ml.ml_mfp != NULL
  			  && curbuf->b_ml.ml_mfp->mf_fname != NULL)
 -	    (void)mch_setperm(curbuf->b_ml.ml_mfp->mf_fname, (long)swap_mode);
 +	{
 +	    char_u *swap_fname = curbuf->b_ml.ml_mfp->mf_fname;
 +
 +	    /*
 +	     * If the group-read bit is set but not the world-read bit, then
 +	     * the group must be equal to the group of the original file.  If
 +	     * we can't make that happen then reset the group-read bit.  This
 +	     * avoids making the swap file readable to more users when the
 +	     * primary group of the user is too permissive.
 +	     */
 +	    if ((swap_mode & 044) == 040)
 +	    {
 +		stat_T	swap_st;
 +
 +		if (mch_stat((char *)swap_fname, &swap_st) >= 0
 +			&& st.st_gid != swap_st.st_gid
 +			&& fchown(curbuf->b_ml.ml_mfp->mf_fd, -1, st.st_gid)
 +									 == -1)
 +		    swap_mode &= 0600;
 +	    }
 +
 +	    (void)mch_setperm(swap_fname, (long)swap_mode);
 +	}
  #endif
      }