Re: [PATCH 3/3] ima: use fs method to read integrity data

[Mimi Zohar]

On Thu, 2017-09-14 at 22:50 -0700, Linus Torvalds wrote:
> This is still wrong.
> 
> (a) there is no explanation for why we need that exclusive lock in the
> first place

> Why should a read need exclusive access? You'd think shared is sufficient.

True, reading a file shouldn't require an exclusive lock. ÂThe
exclusive lock is taken to prevent the file from changing while the
file hash is being calculated.

> But regardless, it needs *explanation*.

Agreed. ÂA fuller explanation was included in the cover letter that
should have also been included in the patch description. ÂThe
following is taken from the cover letter:

With the introduction of IMA-appraisal and the need to write file
hashes as security xattrs, IMA needed to take the global i_mutex
lock.ÂÂprocess_measurement() took the iint->mutex first and then
the i_mutex, while setxattr, chmod and chown took the locks in
reverse order.ÂÂTo resolve this potential deadlock, the iint->mutex
was removed.

Some filesystems have recently replaced their filesystem dependent
lock with the global i_rwsem (formerly the i_mutex) to read a file.
As a result, when IMA attempts to calculate the file hash, reading
the file attempts to take the i_rwsem again.

To resolve this locking problem, this patch set defines a new
->integrity_read file operation method.

(Fixes: Commit 6552321831dc "xfs: remove i_iolock and use i_rwsem in
the VFS inode instead")

Mimi

> (b) the lockdep test isn't for the exclusive lock that the code comment
> says it is
> 
> So no, this needs more work.
>Â
>ÂÂÂÂÂLinus
>Â

> 
> On Sep 14, 2017 21:59, "Mimi Zohar" <zohar@xxxxxxxxxxxxxxxxxx> wrote:
> 
> > From: Christoph Hellwig <hch@xxxxxx>
> >
> > Add a new ->integrity_read file operation to read data for integrity
> > hash collection.  This is defined to be equivalent to ->read_iter,
> > except that it will be called with the i_rwsem held exclusively.
> >
> > (Based on Christoph's original patch.)
> >
> > Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> > Cc: Matthew Garrett <mjg59@xxxxxxxxxxxxx>
> > Cc: Jan Kara <jack@xxxxxxxx>
> > Cc: "Theodore Ts'o" <tytso@xxxxxxx>
> > Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx>
> > Cc: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> > Cc: Chao Yu <yuchao0@xxxxxxxxxx>
> > Cc: Steven Whitehouse <swhiteho@xxxxxxxxxx>
> > Cc: Bob Peterson <rpeterso@xxxxxxxxxx>
> > Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
> > Cc: Dave Kleikamp <shaggy@xxxxxxxxxx>
> > Cc: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxxxxxx>
> > Cc: Mark Fasheh <mfasheh@xxxxxxxxxxx>
> > Cc: Joel Becker <jlbec@xxxxxxxxxxxx>
> > Cc: Richard Weinberger <richard@xxxxxx>
> > Cc: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx>
> > Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> > Cc: Chris Mason <clm@xxxxxx>
> > Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
> > Reviewed-by: Jan Kara <jack@xxxxxxx>
> > Reviewed-by: Dmitry Kasatkin <dmitry.kasatkin@xxxxxxxxxx>
> > ---
> >  fs/btrfs/file.c           |  1 +
> >  fs/efivarfs/file.c        |  1 +
> >  fs/ext2/file.c            | 17 +++++++++++++++++
> >  fs/ext4/file.c            | 20 ++++++++++++++++++++
> >  fs/f2fs/file.c            |  1 +
> >  fs/jffs2/file.c           |  1 +
> >  fs/jfs/file.c             |  1 +
> >  fs/nilfs2/file.c          |  1 +
> >  fs/ramfs/file-mmu.c       |  1 +
> >  fs/ramfs/file-nommu.c     |  1 +
> >  fs/ubifs/file.c           |  1 +
> >  fs/xfs/xfs_file.c         | 21 +++++++++++++++++++++
> >  include/linux/fs.h        |  1 +
> >  mm/shmem.c                |  1 +
> >  security/integrity/iint.c | 20 ++++++++++++++------
> >  15 files changed, 83 insertions(+), 6 deletions(-)
> >
> > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> > index 9e75d8a39aac..2542dc66c85c 100644
> > --- a/fs/btrfs/file.c
> > +++ b/fs/btrfs/file.c
> > @@ -3125,6 +3125,7 @@ const struct file_operations btrfs_file_operations =
> > {
> >  #endif
> >         .clone_file_range = btrfs_clone_file_range,
> >         .dedupe_file_range = btrfs_dedupe_file_range,
> > +       .integrity_read = generic_file_read_iter,
> >  };
> >
> >  void btrfs_auto_defrag_exit(void)
> > diff --git a/fs/efivarfs/file.c b/fs/efivarfs/file.c
> > index 863f1b100165..17955a92a5b3 100644
> > --- a/fs/efivarfs/file.c
> > +++ b/fs/efivarfs/file.c
> > @@ -179,4 +179,5 @@ const struct file_operations efivarfs_file_operations
> > = {
> >         .write  = efivarfs_file_write,
> >         .llseek = no_llseek,
> >         .unlocked_ioctl = efivarfs_file_ioctl,
> > +       .integrity_read = efivarfs_file_read_iter,
> >  };
> > diff --git a/fs/ext2/file.c b/fs/ext2/file.c
> > index d34d32bdc944..111069de1973 100644
> > --- a/fs/ext2/file.c
> > +++ b/fs/ext2/file.c
> > @@ -192,6 +192,22 @@ static ssize_t ext2_file_read_iter(struct kiocb
> > *iocb, struct iov_iter *to)
> >         return generic_file_read_iter(iocb, to);
> >  }
> >
> > +static ssize_t ext2_file_integrity_read_iter(struct kiocb *iocb,
> > +                                            struct iov_iter *to)
> > +{
> > +       struct inode *inode = file_inode(iocb->ki_filp);
> > +
> > +       lockdep_assert_held(&inode->i_rwsem);
> > +#ifdef CONFIG_FS_DAX
> > +       if (!iov_iter_count(to))
> > +               return 0; /* skip atime */
> > +
> > +       if (IS_DAX(iocb->ki_filp->f_mapping->host))
> > +               return dax_iomap_rw(iocb, to, &ext2_iomap_ops);
> > +#endif
> > +       return generic_file_read_iter(iocb, to);
> > +}
> > +
> >  static ssize_t ext2_file_write_iter(struct kiocb *iocb, struct iov_iter
> > *from)
> >  {
> >  #ifdef CONFIG_FS_DAX
> > @@ -216,6 +232,7 @@ const struct file_operations ext2_file_operations = {
> >         .get_unmapped_area = thp_get_unmapped_area,
> >         .splice_read    = generic_file_splice_read,
> >         .splice_write   = iter_file_splice_write,
> > +       .integrity_read = ext2_file_integrity_read_iter,
> >  };
> >
> >  const struct inode_operations ext2_file_inode_operations = {
> > diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> > index 58294c9a7e1d..3ab4105c8578 100644
> > --- a/fs/ext4/file.c
> > +++ b/fs/ext4/file.c
> > @@ -74,6 +74,25 @@ static ssize_t ext4_file_read_iter(struct kiocb *iocb,
> > struct iov_iter *to)
> >         return generic_file_read_iter(iocb, to);
> >  }
> >
> > +static ssize_t ext4_file_integrity_read_iter(struct kiocb *iocb,
> > +                                            struct iov_iter *to)
> > +{
> > +       struct inode *inode = file_inode(iocb->ki_filp);
> > +
> > +       lockdep_assert_held(&inode->i_rwsem);
> > +       if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
> > +               return -EIO;
> > +
> > +       if (!iov_iter_count(to))
> > +               return 0; /* skip atime */
> > +
> > +#ifdef CONFIG_FS_DAX
> > +       if (IS_DAX(inode))
> > +               return dax_iomap_rw(iocb, to, &ext4_iomap_ops);
> > +#endif
> > +       return generic_file_read_iter(iocb, to);
> > +}
> > +
> >  /*
> >   * Called when an inode is released. Note that this is different
> >   * from ext4_file_open: open gets called at every open, but release
> > @@ -747,6 +766,7 @@ const struct file_operations ext4_file_operations = {
> >         .splice_read    = generic_file_splice_read,
> >         .splice_write   = iter_file_splice_write,
> >         .fallocate      = ext4_fallocate,
> > +       .integrity_read = ext4_file_integrity_read_iter,
> >  };
> >
> >  const struct inode_operations ext4_file_inode_operations = {
> > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > index 2706130c261b..82ea81da0b2d 100644
> > --- a/fs/f2fs/file.c
> > +++ b/fs/f2fs/file.c
> > @@ -2514,4 +2514,5 @@ const struct file_operations f2fs_file_operations = {
> >  #endif
> >         .splice_read    = generic_file_splice_read,
> >         .splice_write   = iter_file_splice_write,
> > +       .integrity_read = generic_file_read_iter,
> >  };
> > diff --git a/fs/jffs2/file.c b/fs/jffs2/file.c
> > index c12476e309c6..5a63034cccf5 100644
> > --- a/fs/jffs2/file.c
> > +++ b/fs/jffs2/file.c
> > @@ -57,6 +57,7 @@ const struct file_operations jffs2_file_operations =
> >         .mmap =         generic_file_readonly_mmap,
> >         .fsync =        jffs2_fsync,
> >         .splice_read =  generic_file_splice_read,
> > +       .integrity_read = generic_file_read_iter,
> >  };
> >
> >  /* jffs2_file_inode_operations */
> > diff --git a/fs/jfs/file.c b/fs/jfs/file.c
> > index 739492c7a3fd..423512a810e4 100644
> > --- a/fs/jfs/file.c
> > +++ b/fs/jfs/file.c
> > @@ -162,4 +162,5 @@ const struct file_operations jfs_file_operations = {
> >  #ifdef CONFIG_COMPAT
> >         .compat_ioctl   = jfs_compat_ioctl,
> >  #endif
> > +       .integrity_read = generic_file_read_iter,
> >  };
> > diff --git a/fs/nilfs2/file.c b/fs/nilfs2/file.c
> > index c5fa3dee72fc..55e058ac487f 100644
> > --- a/fs/nilfs2/file.c
> > +++ b/fs/nilfs2/file.c
> > @@ -150,6 +150,7 @@ const struct file_operations nilfs_file_operations = {
> >         /* .release     = nilfs_release_file, */
> >         .fsync          = nilfs_sync_file,
> >         .splice_read    = generic_file_splice_read,
> > +       .integrity_read = generic_file_read_iter,
> >  };
> >
> >  const struct inode_operations nilfs_file_inode_operations = {
> > diff --git a/fs/ramfs/file-mmu.c b/fs/ramfs/file-mmu.c
> > index 12af0490322f..4f24d1b589b1 100644
> > --- a/fs/ramfs/file-mmu.c
> > +++ b/fs/ramfs/file-mmu.c
> > @@ -47,6 +47,7 @@ const struct file_operations ramfs_file_operations = {
> >         .splice_write   = iter_file_splice_write,
> >         .llseek         = generic_file_llseek,
> >         .get_unmapped_area      = ramfs_mmu_get_unmapped_area,
> > +       .integrity_read = generic_file_read_iter,
> >  };
> >
> >  const struct inode_operations ramfs_file_inode_operations = {
> > diff --git a/fs/ramfs/file-nommu.c b/fs/ramfs/file-nommu.c
> > index 2ef7ce75c062..5ee704fa84e0 100644
> > --- a/fs/ramfs/file-nommu.c
> > +++ b/fs/ramfs/file-nommu.c
> > @@ -50,6 +50,7 @@ const struct file_operations ramfs_file_operations = {
> >         .splice_read            = generic_file_splice_read,
> >         .splice_write           = iter_file_splice_write,
> >         .llseek                 = generic_file_llseek,
> > +       .integrity_read         = generic_file_read_iter,
> >  };
> >
> >  const struct inode_operations ramfs_file_inode_operations = {
> > diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
> > index 8cad0b19b404..5e52a315e18b 100644
> > --- a/fs/ubifs/file.c
> > +++ b/fs/ubifs/file.c
> > @@ -1747,4 +1747,5 @@ const struct file_operations ubifs_file_operations =
> > {
> >  #ifdef CONFIG_COMPAT
> >         .compat_ioctl   = ubifs_compat_ioctl,
> >  #endif
> > +       .integrity_read = generic_file_read_iter,
> >  };
> > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> > index c4893e226fd8..0a6704b563d6 100644
> > --- a/fs/xfs/xfs_file.c
> > +++ b/fs/xfs/xfs_file.c
> > @@ -292,6 +292,26 @@ xfs_file_read_iter(
> >         return ret;
> >  }
> >
> > +static ssize_t
> > +xfs_integrity_read(
> > +       struct kiocb            *iocb,
> > +       struct iov_iter         *to)
> > +{
> > +       struct inode            *inode = file_inode(iocb->ki_filp);
> > +       struct xfs_mount        *mp = XFS_I(inode)->i_mount;
> > +
> > +       lockdep_assert_held(&inode->i_rwsem);
> > +
> > +       XFS_STATS_INC(mp, xs_read_calls);
> > +
> > +       if (XFS_FORCED_SHUTDOWN(mp))
> > +               return -EIO;
> > +
> > +       if (IS_DAX(inode))
> > +               return dax_iomap_rw(iocb, to, &xfs_iomap_ops);
> > +       return generic_file_read_iter(iocb, to);
> > +}
> > +
> >  /*
> >   * Zero any on disk space between the current EOF and the new, larger EOF.
> >   *
> > @@ -1175,6 +1195,7 @@ const struct file_operations xfs_file_operations = {
> >         .fallocate      = xfs_file_fallocate,
> >         .clone_file_range = xfs_file_clone_range,
> >         .dedupe_file_range = xfs_file_dedupe_range,
> > +       .integrity_read = xfs_integrity_read,
> >  };
> >
> >  const struct file_operations xfs_dir_file_operations = {
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index e522d25d0836..f6a01d3efce5 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -1699,6 +1699,7 @@ struct file_operations {
> >                         u64);
> >         ssize_t (*dedupe_file_range)(struct file *, u64, u64, struct file
> > *,
> >                         u64);
> > +       ssize_t (*integrity_read)(struct kiocb *, struct iov_iter *);
> >  } __randomize_layout;
> >
> >  struct inode_operations {
> > diff --git a/mm/shmem.c b/mm/shmem.c
> > index b0aa6075d164..805d99011ca4 100644
> > --- a/mm/shmem.c
> > +++ b/mm/shmem.c
> > @@ -3849,6 +3849,7 @@ static const struct file_operations
> > shmem_file_operations = {
> >         .splice_read    = generic_file_splice_read,
> >         .splice_write   = iter_file_splice_write,
> >         .fallocate      = shmem_fallocate,
> > +       .integrity_read = shmem_file_read_iter,
> >  #endif
> >  };
> >
> > diff --git a/security/integrity/iint.c b/security/integrity/iint.c
> > index c84e05866052..c3a07276f745 100644
> > --- a/security/integrity/iint.c
> > +++ b/security/integrity/iint.c
> > @@ -21,6 +21,7 @@
> >  #include <linux/rbtree.h>
> >  #include <linux/file.h>
> >  #include <linux/uaccess.h>
> > +#include <linux/uio.h>
> >  #include "integrity.h"
> >
> >  static struct rb_root integrity_iint_tree = RB_ROOT;
> > @@ -184,18 +185,25 @@ security_initcall(integrity_iintcache_init);
> >  int integrity_kernel_read(struct file *file, loff_t offset,
> >                           void *addr, unsigned long count)
> >  {
> > -       mm_segment_t old_fs;
> > -       char __user *buf = (char __user *)addr;
> > +       struct inode *inode = file_inode(file);
> > +       struct kvec iov = { .iov_base = addr, .iov_len = count };
> > +       struct kiocb kiocb;
> > +       struct iov_iter iter;
> >         ssize_t ret;
> >
> > +       lockdep_assert_held(&inode->i_rwsem);
> > +
> >         if (!(file->f_mode & FMODE_READ))
> >                 return -EBADF;
> > +       if (!file->f_op->integrity_read)
> > +               return -EBADF;
> >
> > -       old_fs = get_fs();
> > -       set_fs(get_ds());
> > -       ret = __vfs_read(file, buf, count, &offset);
> > -       set_fs(old_fs);
> > +       init_sync_kiocb(&kiocb, file);
> > +       kiocb.ki_pos = offset;
> > +       iov_iter_kvec(&iter, READ | ITER_KVEC, &iov, 1, count);
> >
> > +       ret = file->f_op->integrity_read(&kiocb, &iter);
> > +       BUG_ON(ret == -EIOCBQUEUED);
> >         return ret;
> >  }
> >
> > --
> > 2.7.4
> >
> >