queue-4.19/ovl-support-stacked-seek_hole-seek_data.patch

   1 From 9e46b840c7053b5f7a245e98cd239b60d189a96c Mon Sep 17 00:00:00 2001
   2 From: Amir Goldstein <amir73il@gmail.com>
   3 Date: Wed, 27 Feb 2019 13:32:11 +0200
   4 Subject: ovl: support stacked SEEK_HOLE/SEEK_DATA
   5
   6 From: Amir Goldstein <amir73il@gmail.com>
   7
   8 commit 9e46b840c7053b5f7a245e98cd239b60d189a96c upstream.
   9
  10 Overlay file f_pos is the master copy that is preserved
  11 through copy up and modified on read/write, but only real
  12 fs knows how to SEEK_HOLE/SEEK_DATA and real fs may impose
  13 limitations that are more strict than ->s_maxbytes for specific
  14 files, so we use the real file to perform seeks.
  15
  16 We do not call real fs for SEEK_CUR:0 query and for SEEK_SET:0
  17 requests.
  18
  19 Fixes: d1d04ef8572b ("ovl: stack file ops")
  20 Reported-by: Eddie Horng <eddiehorng.tw@gmail.com>
  21 Signed-off-by: Amir Goldstein <amir73il@gmail.com>
  22 Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
  23 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  24
  25 ---
  26  fs/overlayfs/file.c |   44 ++++++++++++++++++++++++++++++++++++++++----
  27  1 file changed, 40 insertions(+), 4 deletions(-)
  28
  29 --- a/fs/overlayfs/file.c
  30 +++ b/fs/overlayfs/file.c
  31 @@ -146,11 +146,47 @@ static int ovl_release(struct inode *ino
  32
  33  static loff_t ovl_llseek(struct file *file, loff_t offset, int whence)
  34  {
  35 -       struct inode *realinode = ovl_inode_real(file_inode(file));
  36 +       struct inode *inode = file_inode(file);
  37 +       struct fd real;
  38 +       const struct cred *old_cred;
  39 +       ssize_t ret;
  40
  41 -       return generic_file_llseek_size(file, offset, whence,
  42 -                                       realinode->i_sb->s_maxbytes,
  43 -                                       i_size_read(realinode));
  44 +       /*
  45 +        * The two special cases below do not need to involve real fs,
  46 +        * so we can optimizing concurrent callers.
  47 +        */
  48 +       if (offset == 0) {
  49 +               if (whence == SEEK_CUR)
  50 +                       return file->f_pos;
  51 +
  52 +               if (whence == SEEK_SET)
  53 +                       return vfs_setpos(file, 0, 0);
  54 +       }
  55 +
  56 +       ret = ovl_real_fdget(file, &real);
  57 +       if (ret)
  58 +               return ret;
  59 +
  60 +       /*
  61 +        * Overlay file f_pos is the master copy that is preserved
  62 +        * through copy up and modified on read/write, but only real
  63 +        * fs knows how to SEEK_HOLE/SEEK_DATA and real fs may impose
  64 +        * limitations that are more strict than ->s_maxbytes for specific
  65 +        * files, so we use the real file to perform seeks.
  66 +        */
  67 +       inode_lock(inode);
  68 +       real.file->f_pos = file->f_pos;
  69 +
  70 +       old_cred = ovl_override_creds(inode->i_sb);
  71 +       ret = vfs_llseek(real.file, offset, whence);
  72 +       revert_creds(old_cred);
  73 +
  74 +       file->f_pos = real.file->f_pos;
  75 +       inode_unlock(inode);
  76 +
  77 +       fdput(real);
  78 +
  79 +       return ret;
  80  }
  81
  82  static void ovl_file_accessed(struct file *file)