/* * Overlayfs NFS export support. * * Amir Goldstein * * Copyright (C) 2017-2018 CTERA Networks. All Rights Reserved. * * This program is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 as published by * the Free Software Foundation. */ #include #include #include #include #include #include #include #include "overlayfs.h" /* * We only need to encode origin if there is a chance that the same object was * encoded pre copy up and then we need to stay consistent with the same * encoding also after copy up. If non-pure upper is not indexed, then it was * copied up before NFS export was enabled. In that case we don't need to worry * about staying consistent with pre copy up encoding and we encode an upper * file handle. Overlay root dentry is a private case of non-indexed upper. * * The following table summarizes the different file handle encodings used for * different overlay object types: * * Object type | Encoding * -------------------------------- * Pure upper | U * Non-indexed upper | U * Indexed upper | L (*) * Non-upper | L (*) * * U = upper file handle * L = lower file handle * * (*) Connecting an overlay dir from real lower dentry is not always * possible when there are redirects in lower layers. To mitigate this case, * we copy up the lower dir first and then encode an upper dir file handle. */ static bool ovl_should_encode_origin(struct dentry *dentry) { struct ovl_fs *ofs = dentry->d_sb->s_fs_info; if (!ovl_dentry_lower(dentry)) return false; /* * Decoding a merge dir, whose origin's parent is under a redirected * lower dir is not always possible. As a simple aproximation, we do * not encode lower dir file handles when overlay has multiple lower * layers and origin is below the topmost lower layer. * * TODO: copy up only the parent that is under redirected lower. */ if (d_is_dir(dentry) && ofs->upper_mnt && OVL_E(dentry)->lowerstack[0].layer->idx > 1) return false; /* Decoding a non-indexed upper from origin is not implemented */ if (ovl_dentry_upper(dentry) && !ovl_test_flag(OVL_INDEX, d_inode(dentry))) return false; return true; } static int ovl_encode_maybe_copy_up(struct dentry *dentry) { int err; if (ovl_dentry_upper(dentry)) return 0; err = ovl_want_write(dentry); if (err) return err; err = ovl_copy_up(dentry); ovl_drop_write(dentry); return err; } static int ovl_d_to_fh(struct dentry *dentry, char *buf, int buflen) { struct dentry *upper; struct dentry *origin = ovl_dentry_lower(dentry); struct ovl_fh *fh = NULL; int err; /* * If we should not encode a lower dir file handle, copy up and encode * an upper dir file handle. */ if (!ovl_should_encode_origin(dentry)) { err = ovl_encode_maybe_copy_up(dentry); if (err) goto fail; origin = NULL; } upper = ovl_dentry_upper(dentry); err = -EACCES; if (!upper || origin) goto fail; /* TODO: encode non pure-upper by origin */ fh = ovl_encode_fh(upper, true); err = -EOVERFLOW; if (fh->len > buflen) goto fail; memcpy(buf, (char *)fh, fh->len); err = fh->len; out: kfree(fh); return err; fail: pr_warn_ratelimited("overlayfs: failed to encode file handle (%pd2, err=%i, buflen=%d, len=%d, type=%d)\n", dentry, err, buflen, fh ? (int)fh->len : 0, fh ? fh->type : 0); goto out; } static int ovl_dentry_to_fh(struct dentry *dentry, u32 *fid, int *max_len) { int res, len = *max_len << 2; res = ovl_d_to_fh(dentry, (char *)fid, len); if (res <= 0) return FILEID_INVALID; len = res; /* Round up to dwords */ *max_len = (len + 3) >> 2; return OVL_FILEID; } static int ovl_encode_inode_fh(struct inode *inode, u32 *fid, int *max_len, struct inode *parent) { struct dentry *dentry; int type; /* TODO: encode connectable file handles */ if (parent) return FILEID_INVALID; dentry = d_find_any_alias(inode); if (WARN_ON(!dentry)) return FILEID_INVALID; type = ovl_dentry_to_fh(dentry, fid, max_len); dput(dentry); return type; } /* * Find or instantiate an overlay dentry from real dentries. */ static struct dentry *ovl_obtain_alias(struct super_block *sb, struct dentry *upper, struct ovl_path *lowerpath) { struct inode *inode; struct dentry *dentry; struct ovl_entry *oe; void *fsdata = &oe; /* TODO: obtain non pure-upper */ if (lowerpath) return ERR_PTR(-EIO); inode = ovl_get_inode(sb, dget(upper), NULL, NULL, 0); if (IS_ERR(inode)) { dput(upper); return ERR_CAST(inode); } dentry = d_find_any_alias(inode); if (!dentry) { dentry = d_alloc_anon(inode->i_sb); if (!dentry) goto nomem; oe = ovl_alloc_entry(0); if (!oe) goto nomem; dentry->d_fsdata = oe; ovl_dentry_set_upper_alias(dentry); } return d_instantiate_anon(dentry, inode); nomem: iput(inode); dput(dentry); return ERR_PTR(-ENOMEM); } /* * Lookup a child overlay dentry to get a connected overlay dentry whose real * dentry is @real. If @real is on upper layer, we lookup a child overlay * dentry with the same name as the real dentry. Otherwise, we need to consult * index for lookup. */ static struct dentry *ovl_lookup_real_one(struct dentry *connected, struct dentry *real, struct ovl_layer *layer) { struct inode *dir = d_inode(connected); struct dentry *this, *parent = NULL; struct name_snapshot name; int err; /* TODO: lookup by lower real dentry */ if (layer->idx) return ERR_PTR(-EACCES); /* * Lookup child overlay dentry by real name. The dir mutex protects us * from racing with overlay rename. If the overlay dentry that is above * real has already been moved to a parent that is not under the * connected overlay dir, we return -ECHILD and restart the lookup of * connected real path from the top. */ inode_lock_nested(dir, I_MUTEX_PARENT); err = -ECHILD; parent = dget_parent(real); if (ovl_dentry_upper(connected) != parent) goto fail; /* * We also need to take a snapshot of real dentry name to protect us * from racing with underlying layer rename. In this case, we don't * care about returning ESTALE, only from dereferencing a free name * pointer because we hold no lock on the real dentry. */ take_dentry_name_snapshot(&name, real); this = lookup_one_len(name.name, connected, strlen(name.name)); err = PTR_ERR(this); if (IS_ERR(this)) { goto fail; } else if (!this || !this->d_inode) { dput(this); err = -ENOENT; goto fail; } else if (ovl_dentry_upper(this) != real) { dput(this); err = -ESTALE; goto fail; } out: release_dentry_name_snapshot(&name); dput(parent); inode_unlock(dir); return this; fail: pr_warn_ratelimited("overlayfs: failed to lookup one by real (%pd2, layer=%d, connected=%pd2, err=%i)\n", real, layer->idx, connected, err); this = ERR_PTR(err); goto out; } /* * Lookup a connected overlay dentry whose real dentry is @real. * If @real is on upper layer, we lookup a child overlay dentry with the same * path the real dentry. Otherwise, we need to consult index for lookup. */ static struct dentry *ovl_lookup_real(struct super_block *sb, struct dentry *real, struct ovl_layer *layer) { struct dentry *connected; int err = 0; /* TODO: use index when looking up by lower real dentry */ if (layer->idx) return ERR_PTR(-EACCES); connected = dget(sb->s_root); while (!err) { struct dentry *next, *this; struct dentry *parent = NULL; struct dentry *real_connected = ovl_dentry_upper(connected); if (real_connected == real) break; /* Find the topmost dentry not yet connected */ next = dget(real); for (;;) { parent = dget_parent(next); if (parent == real_connected) break; /* * If real has been moved out of 'real_connected', * we will not find 'real_connected' and hit the layer * root. In that case, we need to restart connecting. * This game can go on forever in the worst case. We * may want to consider taking s_vfs_rename_mutex if * this happens more than once. */ if (parent == layer->mnt->mnt_root) { dput(connected); connected = dget(sb->s_root); break; } /* * If real file has been moved out of the layer root * directory, we will eventully hit the real fs root. * This cannot happen by legit overlay rename, so we * return error in that case. */ if (parent == next) { err = -EXDEV; break; } dput(next); next = parent; } if (!err) { this = ovl_lookup_real_one(connected, next, layer); if (IS_ERR(this)) err = PTR_ERR(this); /* * Lookup of child in overlay can fail when racing with * overlay rename of child away from 'connected' parent. * In this case, we need to restart the lookup from the * top, because we cannot trust that 'real_connected' is * still an ancestor of 'real'. */ if (err == -ECHILD) { this = dget(sb->s_root); err = 0; } if (!err) { dput(connected); connected = this; } } dput(parent); dput(next); } if (err) goto fail; return connected; fail: pr_warn_ratelimited("overlayfs: failed to lookup by real (%pd2, layer=%d, connected=%pd2, err=%i)\n", real, layer->idx, connected, err); dput(connected); return ERR_PTR(err); } /* * Get an overlay dentry from upper/lower real dentries. */ static struct dentry *ovl_get_dentry(struct super_block *sb, struct dentry *upper, struct ovl_path *lowerpath) { struct ovl_fs *ofs = sb->s_fs_info; struct ovl_layer upper_layer = { .mnt = ofs->upper_mnt }; /* TODO: get non-upper dentry */ if (!upper) return ERR_PTR(-EACCES); /* * Obtain a disconnected overlay dentry from a non-dir real upper * dentry. */ if (!d_is_dir(upper)) return ovl_obtain_alias(sb, upper, NULL); /* Removed empty directory? */ if ((upper->d_flags & DCACHE_DISCONNECTED) || d_unhashed(upper)) return ERR_PTR(-ENOENT); /* * If real upper dentry is connected and hashed, get a connected * overlay dentry with the same path as the real upper dentry. */ return ovl_lookup_real(sb, upper, &upper_layer); } static struct dentry *ovl_upper_fh_to_d(struct super_block *sb, struct ovl_fh *fh) { struct ovl_fs *ofs = sb->s_fs_info; struct dentry *dentry; struct dentry *upper; if (!ofs->upper_mnt) return ERR_PTR(-EACCES); upper = ovl_decode_fh(fh, ofs->upper_mnt); if (IS_ERR_OR_NULL(upper)) return upper; dentry = ovl_get_dentry(sb, upper, NULL); dput(upper); return dentry; } static struct dentry *ovl_fh_to_dentry(struct super_block *sb, struct fid *fid, int fh_len, int fh_type) { struct dentry *dentry = NULL; struct ovl_fh *fh = (struct ovl_fh *) fid; int len = fh_len << 2; unsigned int flags = 0; int err; err = -EINVAL; if (fh_type != OVL_FILEID) goto out_err; err = ovl_check_fh_len(fh, len); if (err) goto out_err; /* TODO: decode non-upper */ flags = fh->flags; if (flags & OVL_FH_FLAG_PATH_UPPER) dentry = ovl_upper_fh_to_d(sb, fh); err = PTR_ERR(dentry); if (IS_ERR(dentry) && err != -ESTALE) goto out_err; return dentry; out_err: pr_warn_ratelimited("overlayfs: failed to decode file handle (len=%d, type=%d, flags=%x, err=%i)\n", len, fh_type, flags, err); return ERR_PTR(err); } static struct dentry *ovl_fh_to_parent(struct super_block *sb, struct fid *fid, int fh_len, int fh_type) { pr_warn_ratelimited("overlayfs: connectable file handles not supported; use 'no_subtree_check' exportfs option.\n"); return ERR_PTR(-EACCES); } static int ovl_get_name(struct dentry *parent, char *name, struct dentry *child) { /* * ovl_fh_to_dentry() returns connected dir overlay dentries and * ovl_fh_to_parent() is not implemented, so we should not get here. */ WARN_ON_ONCE(1); return -EIO; } static struct dentry *ovl_get_parent(struct dentry *dentry) { /* * ovl_fh_to_dentry() returns connected dir overlay dentries, so we * should not get here. */ WARN_ON_ONCE(1); return ERR_PTR(-EIO); } const struct export_operations ovl_export_operations = { .encode_fh = ovl_encode_inode_fh, .fh_to_dentry = ovl_fh_to_dentry, .fh_to_parent = ovl_fh_to_parent, .get_name = ovl_get_name, .get_parent = ovl_get_parent, };