text: // SPDX-License-Identifier: GPL-2.0+
  /*
   * Copyright (C) 2017 Oracle.  All Rights Reserved.
   * Author: Darrick J. Wong <darrick.wong@oracle.com>
   */
  #include "xfs.h"
  #include "xfs_fs.h"
  #include "xfs_shared.h"
  #include "xfs_format.h"
  #include "xfs_trans_resv.h"
  #include "xfs_mount.h"
  #include "xfs_log_format.h"
  #include "xfs_inode.h"
  #include "xfs_icache.h"
  #include "xfs_dir2.h"
  #include "xfs_dir2_priv.h"
  #include "scrub/scrub.h"
  #include "scrub/common.h"
  
  /* Set us up to scrub parents. */
  int
  xchk_setup_parent(
  	struct xfs_scrub	*sc,
  	struct xfs_inode	*ip)
  {
  	return xchk_setup_inode_contents(sc, ip, 0);
  }
  
  /* Parent pointers */
  
  /* Look for an entry in a parent pointing to this inode. */
  
  struct xchk_parent_ctx {
  	struct dir_context	dc;
  	struct xfs_scrub	*sc;
  	xfs_ino_t		ino;
  	xfs_nlink_t		nlink;
  	bool			cancelled;
  };
  
  /* Look for a single entry in a directory pointing to an inode. */
  STATIC int
  xchk_parent_actor(
  	struct dir_context	*dc,
  	const char		*name,
  	int			namelen,
  	loff_t			pos,
  	u64			ino,
  	unsigned		type)
  {
  	struct xchk_parent_ctx	*spc;
  	int			error = 0;
  
  	spc = container_of(dc, struct xchk_parent_ctx, dc);
  	if (spc->ino == ino)
  		spc->nlink++;
  
  	/*
  	 * If we're facing a fatal signal, bail out.  Store the cancellation
  	 * status separately because the VFS readdir code squashes error codes
  	 * into short directory reads.
  	 */
  	if (xchk_should_terminate(spc->sc, &error))
  		spc->cancelled = true;
  
  	return error;
  }
  
  /* Count the number of dentries in the parent dir that point to this inode. */
  STATIC int
  xchk_parent_count_parent_dentries(
  	struct xfs_scrub	*sc,
  	struct xfs_inode	*parent,
  	xfs_nlink_t		*nlink)
  {
  	struct xchk_parent_ctx	spc = {
  		.dc.actor	= xchk_parent_actor,
  		.ino		= sc->ip->i_ino,
  		.sc		= sc,
  	};
  	size_t			bufsize;
  	loff_t			oldpos;
  	uint			lock_mode;
  	int			error = 0;
  
  	/*
  	 * If there are any blocks, read-ahead block 0 as we're almost
  	 * certain to have the next operation be a read there.  This is
  	 * how we guarantee that the parent's extent map has been loaded,
  	 * if there is one.
  	 */
  	lock_mode = xfs_ilock_data_map_shared(parent);
  	if (parent->i_df.if_nextents > 0)
  		error = xfs_dir3_data_readahead(parent, 0, 0);
  	xfs_iunlock(parent, lock_mode);
  	if (error)
  		return error;
  
  	/*
  	 * Iterate the parent dir to confirm that there is
  	 * exactly one entry pointing back to the inode being
  	 * scanned.
  	 */
  	bufsize = (size_t)min_t(loff_t, XFS_READDIR_BUFSIZE,
  			parent->i_d.di_size);
  	oldpos = 0;
  	while (true) {
  		error = xfs_readdir(sc->tp, parent, &spc.dc, bufsize);
  		if (error)
  			goto out;
  		if (spc.cancelled) {
  			error = -EAGAIN;
  			goto out;
  		}
  		if (oldpos == spc.dc.pos)
  			break;
  		oldpos = spc.dc.pos;
  	}
  	*nlink = spc.nlink;
  out:
  	return error;
  }
  
  /*
   * Given the inode number of the alleged parent of the inode being
   * scrubbed, try to validate that the parent has exactly one directory
   * entry pointing back to the inode being scrubbed.
   */
  STATIC int
  xchk_parent_validate(
  	struct xfs_scrub	*sc,
  	xfs_ino_t		dnum,
  	bool			*try_again)
  {
  	struct xfs_mount	*mp = sc->mp;
  	struct xfs_inode	*dp = NULL;
  	xfs_nlink_t		expected_nlink;
  	xfs_nlink_t		nlink;
  	int			error = 0;
  
  	*try_again = false;
  
  	if (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)
  		goto out;
  
  	/* '..' must not point to ourselves. */
  	if (sc->ip->i_ino == dnum) {
  		xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
  		goto out;
  	}
  
  	/*
  	 * If we're an unlinked directory, the parent /won't/ have a link
  	 * to us.  Otherwise, it should have one link.
  	 */
  	expected_nlink = VFS_I(sc->ip)->i_nlink == 0 ? 0 : 1;
  
  	/*
  	 * Grab this parent inode.  We release the inode before we
  	 * cancel the scrub transaction.  Since we're don't know a
  	 * priori that releasing the inode won't trigger eofblocks
  	 * cleanup (which allocates what would be a nested transaction)
  	 * if the parent pointer erroneously points to a file, we
  	 * can't use DONTCACHE here because DONTCACHE inodes can trigger
  	 * immediate inactive cleanup of the inode.
  	 *
  	 * If _iget returns -EINVAL or -ENOENT then the parent inode number is
  	 * garbage and the directory is corrupt.  If the _iget returns
  	 * -EFSCORRUPTED or -EFSBADCRC then the parent is corrupt which is a
  	 *  cross referencing error.  Any other error is an operational error.
  	 */
  	error = xfs_iget(mp, sc->tp, dnum, XFS_IGET_UNTRUSTED, 0, &dp);
  	if (error == -EINVAL || error == -ENOENT) {
  		error = -EFSCORRUPTED;
  		xchk_fblock_process_error(sc, XFS_DATA_FORK, 0, &error);
  		goto out;
  	}
  	if (!xchk_fblock_xref_process_error(sc, XFS_DATA_FORK, 0, &error))
  		goto out;
  	if (dp == sc->ip || !S_ISDIR(VFS_I(dp)->i_mode)) {
  		xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
  		goto out_rele;
  	}
  
  	/*
  	 * We prefer to keep the inode locked while we lock and search
  	 * its alleged parent for a forward reference.  If we can grab
  	 * the iolock, validate the pointers and we're done.  We must
  	 * use nowait here to avoid an ABBA deadlock on the parent and
  	 * the child inodes.
  	 */
  	if (xfs_ilock_nowait(dp, XFS_IOLOCK_SHARED)) {
  		error = xchk_parent_count_parent_dentries(sc, dp, &nlink);
  		if (!xchk_fblock_xref_process_error(sc, XFS_DATA_FORK, 0,
  				&error))
  			goto out_unlock;
  		if (nlink != expected_nlink)
  			xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
  		goto out_unlock;
  	}
  
  	/*
  	 * The game changes if we get here.  We failed to lock the parent,
  	 * so we're going to try to verify both pointers while only holding
  	 * one lock so as to avoid deadlocking with something that's actually
  	 * trying to traverse down the directory tree.
  	 */
  	xfs_iunlock(sc->ip, sc->ilock_flags);
  	sc->ilock_flags = 0;
  	error = xchk_ilock_inverted(dp, XFS_IOLOCK_SHARED);
  	if (error)
  		goto out_rele;
  
  	/* Go looking for our dentry. */
  	error = xchk_parent_count_parent_dentries(sc, dp, &nlink);
  	if (!xchk_fblock_xref_process_error(sc, XFS_DATA_FORK, 0, &error))
  		goto out_unlock;
  
  	/* Drop the parent lock, relock this inode. */
  	xfs_iunlock(dp, XFS_IOLOCK_SHARED);
  	error = xchk_ilock_inverted(sc->ip, XFS_IOLOCK_EXCL);
  	if (error)
  		goto out_rele;
  	sc->ilock_flags = XFS_IOLOCK_EXCL;
  
  	/*
  	 * If we're an unlinked directory, the parent /won't/ have a link
  	 * to us.  Otherwise, it should have one link.  We have to re-set
  	 * it here because we dropped the lock on sc->ip.
  	 */
  	expected_nlink = VFS_I(sc->ip)->i_nlink == 0 ? 0 : 1;
  
  	/* Look up '..' to see if the inode changed. */
  	error = xfs_dir_lookup(sc->tp, sc->ip, &xfs_name_dotdot, &dnum, NULL);
  	if (!xchk_fblock_process_error(sc, XFS_DATA_FORK, 0, &error))
  		goto out_rele;
  
  	/* Drat, parent changed.  Try again! */
  	if (dnum != dp->i_ino) {
  		xfs_irele(dp);
  		*try_again = true;
  		return 0;
  	}
  	xfs_irele(dp);
  
  	/*
  	 * '..' didn't change, so check that there was only one entry
  	 * for us in the parent.
  	 */
  	if (nlink != expected_nlink)
  		xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
  	return error;
  
  out_unlock:
  	xfs_iunlock(dp, XFS_IOLOCK_SHARED);
  out_rele:
  	xfs_irele(dp);
  out:
  	return error;
  }
  
  /* Scrub a parent pointer. */
  int
  xchk_parent(
  	struct xfs_scrub	*sc)
  {
  	struct xfs_mount	*mp = sc->mp;
  	xfs_ino_t		dnum;
  	bool			try_again;
  	int			tries = 0;
  	int			error = 0;
  
  	/*
  	 * If we're a directory, check that the '..' link points up to
  	 * a directory that has one entry pointing to us.
  	 */
  	if (!S_ISDIR(VFS_I(sc->ip)->i_mode))
  		return -ENOENT;
  
  	/* We're not a special inode, are we? */
  	if (!xfs_verify_dir_ino(mp, sc->ip->i_ino)) {
  		xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
  		goto out;
  	}
  
  	/*
  	 * The VFS grabs a read or write lock via i_rwsem before it reads
  	 * or writes to a directory.  If we've gotten this far we've
  	 * already obtained IOLOCK_EXCL, which (since 4.10) is the same as
  	 * getting a write lock on i_rwsem.  Therefore, it is safe for us
  	 * to drop the ILOCK here in order to do directory lookups.
  	 */
  	sc->ilock_flags &= ~(XFS_ILOCK_EXCL | XFS_MMAPLOCK_EXCL);
  	xfs_iunlock(sc->ip, XFS_ILOCK_EXCL | XFS_MMAPLOCK_EXCL);
  
  	/* Look up '..' */
  	error = xfs_dir_lookup(sc->tp, sc->ip, &xfs_name_dotdot, &dnum, NULL);
  	if (!xchk_fblock_process_error(sc, XFS_DATA_FORK, 0, &error))
  		goto out;
  	if (!xfs_verify_dir_ino(mp, dnum)) {
  		xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
  		goto out;
  	}
  
  	/* Is this the root dir?  Then '..' must point to itself. */
  	if (sc->ip == mp->m_rootip) {
  		if (sc->ip->i_ino != mp->m_sb.sb_rootino ||
  		    sc->ip->i_ino != dnum)
  			xchk_fblock_set_corrupt(sc, XFS_DATA_FORK, 0);
  		goto out;
  	}
  
  	do {
  		error = xchk_parent_validate(sc, dnum, &try_again);
  		if (error)
  			goto out;
  	} while (try_again && ++tries < 20);
  
  	/*
  	 * We gave it our best shot but failed, so mark this scrub
  	 * incomplete.  Userspace can decide if it wants to try again.
  	 */
  	if (try_again && tries == 20)
  		xchk_set_incomplete(sc);
  out:
  	/*
  	 * If we failed to lock the parent inode even after a retry, just mark
  	 * this scrub incomplete and return.
  	 */
  	if ((sc->flags & XCHK_TRY_HARDER) && error == -EDEADLOCK) {
  		error = 0;
  		xchk_set_incomplete(sc);
  	}
  	return error;
  }
  