releases/4.19.54/abort-file_remove_privs-for-non-reg.-files.patch

   1 From f69e749a49353d96af1a293f56b5b56de59c668a Mon Sep 17 00:00:00 2001
   2 From: Alexander Lochmann <alexander.lochmann@tu-dortmund.de>
   3 Date: Fri, 14 Dec 2018 11:55:52 +0100
   4 Subject: Abort file_remove_privs() for non-reg. files
   5
   6 From: Alexander Lochmann <alexander.lochmann@tu-dortmund.de>
   7
   8 commit f69e749a49353d96af1a293f56b5b56de59c668a upstream.
   9
  10 file_remove_privs() might be called for non-regular files, e.g.
  11 blkdev inode. There is no reason to do its job on things
  12 like blkdev inodes, pipes, or cdevs. Hence, abort if
  13 file does not refer to a regular inode.
  14
  15 AV: more to the point, for devices there might be any number of
  16 inodes refering to given device.  Which one to strip the permissions
  17 from, even if that made any sense in the first place?  All of them
  18 will be observed with contents modified, after all.
  19
  20 Found by LockDoc (Alexander Lochmann, Horst Schirmeier and Olaf
  21 Spinczyk)
  22
  23 Reviewed-by: Jan Kara <jack@suse.cz>
  24 Signed-off-by: Alexander Lochmann <alexander.lochmann@tu-dortmund.de>
  25 Signed-off-by: Horst Schirmeier <horst.schirmeier@tu-dortmund.de>
  26 Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
  27 Cc: Zubin Mithra <zsm@chromium.org>
  28 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  29
  30 ---
  31  fs/inode.c |    9 +++++++--
  32  1 file changed, 7 insertions(+), 2 deletions(-)
  33
  34 --- a/fs/inode.c
  35 +++ b/fs/inode.c
  36 @@ -1817,8 +1817,13 @@ int file_remove_privs(struct file *file)
  37         int kill;
  38         int error = 0;
  39
  40 -       /* Fast path for nothing security related */
  41 -       if (IS_NOSEC(inode))
  42 +       /*
  43 +        * Fast path for nothing security related.
  44 +        * As well for non-regular files, e.g. blkdev inodes.
  45 +        * For example, blkdev_write_iter() might get here
  46 +        * trying to remove privs which it is not allowed to.
  47 +        */
  48 +       if (IS_NOSEC(inode) || !S_ISREG(inode->i_mode))
  49                 return 0;
  50
  51         kill = dentry_needs_remove_privs(dentry);