diff options
Diffstat (limited to 'fs/overlayfs/export.c')
| -rw-r--r-- | fs/overlayfs/export.c | 715 |
1 files changed, 715 insertions, 0 deletions
diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c new file mode 100644 index 000000000000..bb94ce9da5c8 --- /dev/null +++ b/fs/overlayfs/export.c @@ -0,0 +1,715 @@ +/* + * Overlayfs NFS export support. + * + * Amir Goldstein <amir73il@gmail.com> + * + * 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 <linux/fs.h> +#include <linux/cred.h> +#include <linux/mount.h> +#include <linux/namei.h> +#include <linux/xattr.h> +#include <linux/exportfs.h> +#include <linux/ratelimit.h> +#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 *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; + } + + /* Encode an upper or origin file handle */ + fh = ovl_encode_fh(origin ?: ovl_dentry_upper(dentry), !origin); + 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_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 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; + + /* We get overlay directory dentries with ovl_lookup_real() */ + if (d_is_dir(upper ?: lower)) + return ERR_PTR(-EIO); + + inode = ovl_get_inode(sb, dget(upper), lower, index, !!lower); + if (IS_ERR(inode)) { + dput(upper); + return ERR_CAST(inode); + } + + if (index) + ovl_set_flag(OVL_INDEX, 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 (!this) + return NULL; + + 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 = IS_ERR(this) ? PTR_ERR(this) : 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 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_fh(fh, ofs->upper_mnt); + 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 = NULL; + bool is_deleted = false; + int err; + + /* First lookup indexed upper by fh */ + if (ofs->indexdir) { + index = ovl_get_index_fh(ofs, fh); + err = PTR_ERR(index); + if (IS_ERR(index)) { + if (err != -ESTALE) + return ERR_PTR(err); + + /* Found a whiteout index - treat as deleted inode */ + is_deleted = true; + index = NULL; + } + } + + /* Then try to get 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; + } + + /* Then lookup origin by fh */ + err = ovl_check_origin_fh(ofs, fh, NULL, &stack); + if (err) { + goto out_err; + } else if (index) { + err = ovl_verify_origin(index, origin.dentry, false); + if (err) + goto out_err; + } else if (is_deleted) { + /* Lookup deleted non-dir by origin inode */ + if (!d_is_dir(origin.dentry)) + inode = ovl_lookup_inode(sb, origin.dentry, false); + err = -ESTALE; + if (!inode || atomic_read(&inode->i_count) == 1) + goto out_err; + + /* Deleted but still open? */ + index = dget(ovl_i_dentry_upper(inode)); + } + + dentry = ovl_get_dentry(sb, NULL, &origin, index); + +out: + dput(origin.dentry); + dput(index); + iput(inode); + 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_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, +}; |