/* * 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" 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) { err = ovl_copy_up(dentry); ovl_drop_write(dentry); } if (err) { pr_warn_ratelimited("overlayfs: failed to copy up on encode (%pd2, err=%i)\n", dentry, err); } return err; } /* * Before encoding a non-upper directory file handle from real layer N, we need * to check if it will be possible to reconnect an overlay dentry from the real * lower decoded dentry. This is done by following the overlay ancestry up to a * "layer N connected" ancestor and verifying that all parents along the way are * "layer N connectable". If an ancestor that is NOT "layer N connectable" is * found, we need to copy up an ancestor, which is "layer N connectable", thus * making that ancestor "layer N connected". For example: * * layer 1: /a * layer 2: /a/b/c * * The overlay dentry /a is NOT "layer 2 connectable", because if dir /a is * copied up and renamed, upper dir /a will be indexed by lower dir /a from * layer 1. The dir /a from layer 2 will never be indexed, so the algorithm (*) * in ovl_lookup_real_ancestor() will not be able to lookup a connected overlay * dentry from the connected lower dentry /a/b/c. * * To avoid this problem on decode time, we need to copy up an ancestor of * /a/b/c, which is "layer 2 connectable", on encode time. That ancestor is * /a/b. After copy up (and index) of /a/b, it will become "layer 2 connected" * and when the time comes to decode the file handle from lower dentry /a/b/c, * ovl_lookup_real_ancestor() will find the indexed ancestor /a/b and decoding * a connected overlay dentry will be accomplished. * * (*) the algorithm in ovl_lookup_real_ancestor() can be improved to lookup an * entry /a in the lower layers above layer N and find the indexed dir /a from * layer 1. If that improvement is made, then the check for "layer N connected" * will need to verify there are no redirects in lower layers above N. In the * example above, /a will be "layer 2 connectable". However, if layer 2 dir /a * is a target of a layer 1 redirect, then /a will NOT be "layer 2 connectable": * * layer 1: /A (redirect = /a) * layer 2: /a/b/c */ /* Return the lowest layer for encoding a connectable file handle */ static int ovl_connectable_layer(struct dentry *dentry) { struct ovl_entry *oe = OVL_E(dentry); /* We can get overlay root from root of any layer */ if (dentry == dentry->d_sb->s_root) return oe->numlower; /* * If it's an unindexed merge dir, then it's not connectable with any * lower layer */ if (ovl_dentry_upper(dentry) && !ovl_test_flag(OVL_INDEX, d_inode(dentry))) return 0; /* We can get upper/overlay path from indexed/lower dentry */ return oe->lowerstack[0].layer->idx; } /* * @dentry is "connected" if all ancestors up to root or a "connected" ancestor * have the same uppermost lower layer as the origin's layer. We may need to * copy up a "connectable" ancestor to make it "connected". A "connected" dentry * cannot become non "connected", so cache positive result in dentry flags. * * Return the connected origin layer or < 0 on error. */ static int ovl_connect_layer(struct dentry *dentry) { struct dentry *next, *parent = NULL; int origin_layer; int err = 0; if (WARN_ON(dentry == dentry->d_sb->s_root) || WARN_ON(!ovl_dentry_lower(dentry))) return -EIO; origin_layer = OVL_E(dentry)->lowerstack[0].layer->idx; if (ovl_dentry_test_flag(OVL_E_CONNECTED, dentry)) return origin_layer; /* Find the topmost origin layer connectable ancestor of @dentry */ next = dget(dentry); for (;;) { parent = dget_parent(next); if (WARN_ON(parent == next)) { err = -EIO; break; } /* * If @parent is not origin layer connectable, then copy up * @next which is origin layer connectable and we are done. */ if (ovl_connectable_layer(parent) < origin_layer) { err = ovl_encode_maybe_copy_up(next); break; } /* If @parent is connected or indexed we are done */ if (ovl_dentry_test_flag(OVL_E_CONNECTED, parent) || ovl_test_flag(OVL_INDEX, d_inode(parent))) break; dput(next); next = parent; } dput(parent); dput(next); if (!err) ovl_dentry_set_flag(OVL_E_CONNECTED, dentry); return err ?: origin_layer; } /* * 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 and non-indexed merge dirs. * To mitigate those case, we may copy up the lower dir ancestor before encode * a lower dir file handle. * * Return 0 for upper file handle, > 0 for lower file handle or < 0 on error. */ static int ovl_check_encode_origin(struct dentry *dentry) { struct ovl_fs *ofs = dentry->d_sb->s_fs_info; /* Upper file handle for pure upper */ if (!ovl_dentry_lower(dentry)) return 0; /* * Upper file handle for non-indexed upper. * * Root is never indexed, so if there's an upper layer, encode upper for * root. */ if (ovl_dentry_upper(dentry) && !ovl_test_flag(OVL_INDEX, d_inode(dentry))) return 0; /* * Decoding a merge dir, whose origin's ancestor is under a redirected * lower dir or under a non-indexed upper is not always possible. * ovl_connect_layer() will try to make origin's layer "connected" by * copying up a "connectable" ancestor. */ if (d_is_dir(dentry) && ofs->upper_mnt) return ovl_connect_layer(dentry); /* Lower file handle for indexed and non-upper dir/non-dir */ return 1; } static int ovl_d_to_fh(struct dentry *dentry, char *buf, int buflen) { struct ovl_fh *fh = NULL; int err, enc_lower; /* * Check if we should encode a lower or upper file handle and maybe * copy up an ancestor to make lower file handle connectable. */ err = enc_lower = ovl_check_encode_origin(dentry); if (enc_lower < 0) goto fail; /* Encode an upper or lower file handle */ fh = ovl_encode_real_fh(enc_lower ? ovl_dentry_lower(dentry) : ovl_dentry_upper(dentry), !enc_lower); err = PTR_ERR(fh); if (IS_ERR(fh)) goto fail; 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_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 and index. */ static struct dentry *ovl_obtain_alias(struct super_block *sb, struct dentry *upper_alias, struct ovl_path *lowerpath, struct dentry *index) { struct dentry *lower = lowerpath ? lowerpath->dentry : NULL; struct dentry *upper = upper_alias ?: index; struct dentry *dentry; struct inode *inode; struct ovl_entry *oe; struct ovl_inode_params oip = { .lowerpath = lowerpath, .index = index, .numlower = !!lower }; /* We get overlay directory dentries with ovl_lookup_real() */ if (d_is_dir(upper ?: lower)) return ERR_PTR(-EIO); oip.upperdentry = dget(upper); inode = ovl_get_inode(sb, &oip); 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(lower ? 1 : 0); if (!oe) goto nomem; if (lower) { oe->lowerstack->dentry = dget(lower); oe->lowerstack->layer = lowerpath->layer; } dentry->d_fsdata = oe; if (upper_alias) ovl_dentry_set_upper_alias(dentry); } return d_instantiate_anon(dentry, inode); nomem: iput(inode); dput(dentry); return ERR_PTR(-ENOMEM); } /* Get the upper or lower dentry in stach whose on layer @idx */ static struct dentry *ovl_dentry_real_at(struct dentry *dentry, int idx) { struct ovl_entry *oe = dentry->d_fsdata; int i; if (!idx) return ovl_dentry_upper(dentry); for (i = 0; i < oe->numlower; i++) { if (oe->lowerstack[i].layer->idx == idx) return oe->lowerstack[i].dentry; } return NULL; } /* * 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; /* * 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_real_at(connected, layer->idx) != 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_real_at(this, layer->idx) != 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; } static struct dentry *ovl_lookup_real(struct super_block *sb, struct dentry *real, struct ovl_layer *layer); /* * Lookup an indexed or hashed overlay dentry by real inode. */ static struct dentry *ovl_lookup_real_inode(struct super_block *sb, struct dentry *real, struct ovl_layer *layer) { struct ovl_fs *ofs = sb->s_fs_info; struct ovl_layer upper_layer = { .mnt = ofs->upper_mnt }; struct dentry *index = NULL; struct dentry *this = NULL; struct inode *inode; /* * Decoding upper dir from index is expensive, so first try to lookup * overlay dentry in inode/dcache. */ inode = ovl_lookup_inode(sb, real, !layer->idx); if (IS_ERR(inode)) return ERR_CAST(inode); if (inode) { this = d_find_any_alias(inode); iput(inode); } /* * For decoded lower dir file handle, lookup index by origin to check * if lower dir was copied up and and/or removed. */ if (!this && layer->idx && ofs->indexdir && !WARN_ON(!d_is_dir(real))) { index = ovl_lookup_index(ofs, NULL, real, false); if (IS_ERR(index)) return index; } /* Get connected upper overlay dir from index */ if (index) { struct dentry *upper = ovl_index_upper(ofs, index); dput(index); if (IS_ERR_OR_NULL(upper)) return upper; /* * ovl_lookup_real() in lower layer may call recursively once to * ovl_lookup_real() in upper layer. The first level call walks * back lower parents to the topmost indexed parent. The second * recursive call walks back from indexed upper to the topmost * connected/hashed upper parent (or up to root). */ this = ovl_lookup_real(sb, upper, &upper_layer); dput(upper); } if (IS_ERR_OR_NULL(this)) return this; if (WARN_ON(ovl_dentry_real_at(this, layer->idx) != real)) { dput(this); this = ERR_PTR(-EIO); } return this; } /* * Lookup an indexed or hashed overlay dentry, whose real dentry is an * ancestor of @real. */ static struct dentry *ovl_lookup_real_ancestor(struct super_block *sb, struct dentry *real, struct ovl_layer *layer) { struct dentry *next, *parent = NULL; struct dentry *ancestor = ERR_PTR(-EIO); if (real == layer->mnt->mnt_root) return dget(sb->s_root); /* Find the topmost indexed or hashed ancestor */ next = dget(real); for (;;) { parent = dget_parent(next); /* * Lookup a matching overlay dentry in inode/dentry * cache or in index by real inode. */ ancestor = ovl_lookup_real_inode(sb, next, layer); if (ancestor) break; if (parent == layer->mnt->mnt_root) { ancestor = dget(sb->s_root); break; } /* * If @real 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) { ancestor = ERR_PTR(-EXDEV); break; } dput(next); next = parent; } dput(parent); dput(next); return ancestor; } /* * 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; connected = ovl_lookup_real_ancestor(sb, real, layer); if (IS_ERR(connected)) return connected; while (!err) { struct dentry *next, *this; struct dentry *parent = NULL; struct dentry *real_connected = ovl_dentry_real_at(connected, layer->idx); 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'. There is a good chance * that the renamed overlay ancestor is now in cache, so * ovl_lookup_real_ancestor() will find it and we can * continue to connect exactly from where lookup failed. */ if (err == -ECHILD) { this = ovl_lookup_real_ancestor(sb, real, layer); err = PTR_ERR_OR_ZERO(this); } 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 and index. */ static struct dentry *ovl_get_dentry(struct super_block *sb, struct dentry *upper, struct ovl_path *lowerpath, struct dentry *index) { struct ovl_fs *ofs = sb->s_fs_info; struct ovl_layer upper_layer = { .mnt = ofs->upper_mnt }; struct ovl_layer *layer = upper ? &upper_layer : lowerpath->layer; struct dentry *real = upper ?: (index ?: lowerpath->dentry); /* * Obtain a disconnected overlay dentry from a non-dir real dentry * and index. */ if (!d_is_dir(real)) return ovl_obtain_alias(sb, upper, lowerpath, index); /* Removed empty directory? */ if ((real->d_flags & DCACHE_DISCONNECTED) || d_unhashed(real)) return ERR_PTR(-ENOENT); /* * If real dentry is connected and hashed, get a connected overlay * dentry whose real dentry is @real. */ return ovl_lookup_real(sb, real, 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_real_fh(fh, ofs->upper_mnt, true); if (IS_ERR_OR_NULL(upper)) return upper; dentry = ovl_get_dentry(sb, upper, NULL, NULL); dput(upper); return dentry; } static struct dentry *ovl_lower_fh_to_d(struct super_block *sb, struct ovl_fh *fh) { struct ovl_fs *ofs = sb->s_fs_info; struct ovl_path origin = { }; struct ovl_path *stack = &origin; struct dentry *dentry = NULL; struct dentry *index = NULL; struct inode *inode; int err; /* First lookup overlay inode in inode cache by origin fh */ err = ovl_check_origin_fh(ofs, fh, false, NULL, &stack); if (err) return ERR_PTR(err); if (!d_is_dir(origin.dentry) || !(origin.dentry->d_flags & DCACHE_DISCONNECTED)) { inode = ovl_lookup_inode(sb, origin.dentry, false); err = PTR_ERR(inode); if (IS_ERR(inode)) goto out_err; if (inode) { dentry = d_find_any_alias(inode); iput(inode); if (dentry) goto out; } } /* Then lookup indexed upper/whiteout by origin fh */ if (ofs->indexdir) { index = ovl_get_index_fh(ofs, fh); err = PTR_ERR(index); if (IS_ERR(index)) { index = NULL; goto out_err; } } /* Then try to get a connected upper dir by index */ if (index && d_is_dir(index)) { struct dentry *upper = ovl_index_upper(ofs, index); err = PTR_ERR(upper); if (IS_ERR_OR_NULL(upper)) goto out_err; dentry = ovl_get_dentry(sb, upper, NULL, NULL); dput(upper); goto out; } /* Find origin.dentry again with ovl_acceptable() layer check */ if (d_is_dir(origin.dentry)) { dput(origin.dentry); origin.dentry = NULL; err = ovl_check_origin_fh(ofs, fh, true, NULL, &stack); if (err) goto out_err; } if (index) { err = ovl_verify_origin(index, origin.dentry, false); if (err) goto out_err; } /* Get a connected non-upper dir or disconnected non-dir */ dentry = ovl_get_dentry(sb, NULL, &origin, index); out: dput(origin.dentry); dput(index); return dentry; out_err: dentry = ERR_PTR(err); goto out; } 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; flags = fh->flags; dentry = (flags & OVL_FH_FLAG_PATH_UPPER) ? ovl_upper_fh_to_d(sb, fh) : ovl_lower_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_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, };