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SubjectRe: [PATCH 3/3] ima: use fs method to read integrity data
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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.  The
exclusive lock is taken to prevent the file from changing while the
file hash is being calculated.

> But regardless, it needs *explanation*.

Agreed.  A fuller explanation was included in the cover letter that
should have also been included in the patch description.  The
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.  process_measurement() took the iint->mutex first and then
the i_mutex, while setxattr, chmod and chown took the locks in
reverse order.  To 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.

>     Linus


>
> On Sep 14, 2017 21:59, "Mimi Zohar" <zohar@linux.vnet.ibm.com> wrote:
>
> > From: Christoph Hellwig <hch@lst.de>
> >
> > 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@lst.de>
> > Cc: Matthew Garrett <mjg59@srcf.ucam.org>
> > Cc: Jan Kara <jack@suse.com>
> > Cc: "Theodore Ts'o" <tytso@mit.edu>
> > Cc: Andreas Dilger <adilger.kernel@dilger.ca>
> > Cc: Jaegeuk Kim <jaegeuk@kernel.org>
> > Cc: Chao Yu <yuchao0@huawei.com>
> > Cc: Steven Whitehouse <swhiteho@redhat.com>
> > Cc: Bob Peterson <rpeterso@redhat.com>
> > Cc: David Woodhouse <dwmw2@infradead.org>
> > Cc: Dave Kleikamp <shaggy@kernel.org>
> > Cc: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
> > Cc: Mark Fasheh <mfasheh@versity.com>
> > Cc: Joel Becker <jlbec@evilplan.org>
> > Cc: Richard Weinberger <richard@nod.at>
> > Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
> > Cc: Hugh Dickins <hughd@google.com>
> > Cc: Chris Mason <clm@fb.com>
> > Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
> > Reviewed-by: Jan Kara <jack@suse.cz>
> > Reviewed-by: Dmitry Kasatkin <dmitry.kasatkin@huawei.com>
> > ---
> > 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
> >
> >

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