/* * Copyright (C) Neil Brown 2002 * Copyright (C) Christoph Hellwig 2007 * * This file contains the code mapping from inodes to NFS file handles, * and for mapping back from file handles to dentries. * * For details on why we do all the strange and hairy things in here * take a look at Documentation/filesystems/Exporting. */ #include <linux/exportfs.h> #include <linux/fs.h> #include <linux/file.h> #include <linux/module.h> #include <linux/mount.h> #include <linux/namei.h> #include <linux/sched.h> #define dprintk(fmt, args...) do{}while(0) static int get_name(struct vfsmount *mnt, struct dentry *dentry, char *name, struct dentry *child); static int exportfs_get_name(struct vfsmount *mnt, struct dentry *dir, char *name, struct dentry *child) { const struct export_operations *nop = dir->d_sb->s_export_op; if (nop->get_name) return nop->get_name(dir, name, child); else return get_name(mnt, dir, name, child); } /* * Check if the dentry or any of it's aliases is acceptable. */ static struct dentry * find_acceptable_alias(struct dentry *result, int (*acceptable)(void *context, struct dentry *dentry), void *context) { struct dentry *dentry, *toput = NULL; if (acceptable(context, result)) return result; spin_lock(&dcache_lock); list_for_each_entry(dentry, &result->d_inode->i_dentry, d_alias) { dget_locked(dentry); spin_unlock(&dcache_lock); if (toput) dput(toput); if (dentry != result && acceptable(context, dentry)) { dput(result); return dentry; } spin_lock(&dcache_lock); toput = dentry; } spin_unlock(&dcache_lock); if (toput) dput(toput); return NULL; } /* * Find root of a disconnected subtree and return a reference to it. */ static struct dentry * find_disconnected_root(struct dentry *dentry) { dget(dentry); spin_lock(&dentry->d_lock); while (!IS_ROOT(dentry) && (dentry->d_parent->d_flags & DCACHE_DISCONNECTED)) { struct dentry *parent = dentry->d_parent; dget(parent); spin_unlock(&dentry->d_lock); dput(dentry); dentry = parent; spin_lock(&dentry->d_lock); } spin_unlock(&dentry->d_lock); return dentry; } /* * Make sure target_dir is fully connected to the dentry tree. * * It may already be, as the flag isn't always updated when connection happens. */ static int reconnect_path(struct vfsmount *mnt, struct dentry *target_dir, char *nbuf) { int noprogress = 0; int err = -ESTALE; /* * It is possible that a confused file system might not let us complete * the path to the root. For example, if get_parent returns a directory * in which we cannot find a name for the child. While this implies a * very sick filesystem we don't want it to cause knfsd to spin. Hence * the noprogress counter. If we go through the loop 10 times (2 is * probably enough) without getting anywhere, we just give up */ while (target_dir->d_flags & DCACHE_DISCONNECTED && noprogress++ < 10) { struct dentry *pd = find_disconnected_root(target_dir); if (!IS_ROOT(pd)) { /* must have found a connected parent - great */ spin_lock(&pd->d_lock); pd->d_flags &= ~DCACHE_DISCONNECTED; spin_unlock(&pd->d_lock); noprogress = 0; } else if (pd == mnt->mnt_sb->s_root) { printk(KERN_ERR "export: Eeek filesystem root is not connected, impossible\n"); spin_lock(&pd->d_lock); pd->d_flags &= ~DCACHE_DISCONNECTED; spin_unlock(&pd->d_lock); noprogress = 0; } else { /* * We have hit the top of a disconnected path, try to * find parent and connect. * * Racing with some other process renaming a directory * isn't much of a problem here. If someone renames * the directory, it will end up properly connected, * which is what we want * * Getting the parent can't be supported generically, * the locking is too icky. * * Instead we just return EACCES. If server reboots * or inodes get flushed, you lose */ struct dentry *ppd = ERR_PTR(-EACCES); struct dentry *npd; mutex_lock(&pd->d_inode->i_mutex); if (mnt->mnt_sb->s_export_op->get_parent) ppd = mnt->mnt_sb->s_export_op->get_parent(pd); mutex_unlock(&pd->d_inode->i_mutex); if (IS_ERR(ppd)) { err = PTR_ERR(ppd); dprintk("%s: get_parent of %ld failed, err %d\n", __func__, pd->d_inode->i_ino, err); dput(pd); break; } dprintk("%s: find name of %lu in %lu\n", __func__, pd->d_inode->i_ino, ppd->d_inode->i_ino); err = exportfs_get_name(mnt, ppd, nbuf, pd); if (err) { dput(ppd); dput(pd); if (err == -ENOENT) /* some race between get_parent and * get_name? just try again */ continue; break; } dprintk("%s: found name: %s\n", __func__, nbuf); mutex_lock(&ppd->d_inode->i_mutex); npd = lookup_one_len(nbuf, ppd, strlen(nbuf)); mutex_unlock(&ppd->d_inode->i_mutex); if (IS_ERR(npd)) { err = PTR_ERR(npd); dprintk("%s: lookup failed: %d\n", __func__, err); dput(ppd); dput(pd); break; } /* we didn't really want npd, we really wanted * a side-effect of the lookup. * hopefully, npd == pd, though it isn't really * a problem if it isn't */ if (npd == pd) noprogress = 0; else printk("%s: npd != pd\n", __func__); dput(npd); dput(ppd); if (IS_ROOT(pd)) { /* something went wrong, we have to give up */ dput(pd); break; } } dput(pd); } if (target_dir->d_flags & DCACHE_DISCONNECTED) { /* something went wrong - oh-well */ if (!err) err = -ESTALE; return err; } return 0; } struct getdents_callback { char *name; /* name that was found. It already points to a buffer NAME_MAX+1 is size */ unsigned long ino; /* the inum we are looking for */ int found; /* inode matched? */ int sequence; /* sequence counter */ }; /* * A rather strange filldir function to capture * the name matching the specified inode number. */ static int filldir_one(void * __buf, const char * name, int len, loff_t pos, u64 ino, unsigned int d_type) { struct getdents_callback *buf = __buf; int result = 0; buf->sequence++; if (buf->ino == ino) { memcpy(buf->name, name, len); buf->name[len] = '\0'; buf->found = 1; result = -1; } return result; } /** * get_name - default export_operations->get_name function * @dentry: the directory in which to find a name * @name: a pointer to a %NAME_MAX+1 char buffer to store the name * @child: the dentry for the child directory. * * calls readdir on the parent until it finds an entry with * the same inode number as the child, and returns that. */ static int get_name(struct vfsmount *mnt, struct dentry *dentry, char *name, struct dentry *child) { const struct cred *cred = current_cred(); struct inode *dir = dentry->d_inode; int error; struct file *file; struct getdents_callback buffer; error = -ENOTDIR; if (!dir || !S_ISDIR(dir->i_mode)) goto out; error = -EINVAL; if (!dir->i_fop) goto out; /* * Open the directory ... */ file = dentry_open(dget(dentry), mntget(mnt), O_RDONLY, cred); error = PTR_ERR(file); if (IS_ERR(file)) goto out; error = -EINVAL; if (!file->f_op->readdir) goto out_close; buffer.name = name; buffer.ino = child->d_inode->i_ino; buffer.found = 0; buffer.sequence = 0; while (1) { int old_seq = buffer.sequence; error = vfs_readdir(file, filldir_one, &buffer); if (buffer.found) { error = 0; break; } if (error < 0) break; error = -ENOENT; if (old_seq == buffer.sequence) break; } out_close: fput(file); out: return error; } /** * export_encode_fh - default export_operations->encode_fh function * @dentry: the dentry to encode * @fh: where to store the file handle fragment * @max_len: maximum length to store there * @connectable: whether to store parent information * * This default encode_fh function assumes that the 32 inode number * is suitable for locating an inode, and that the generation number * can be used to check that it is still valid. It places them in the * filehandle fragment where export_decode_fh expects to find them. */ static int export_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len, int connectable) { struct inode * inode = dentry->d_inode; int len = *max_len; int type = FILEID_INO32_GEN; if (len < 2 || (connectable && len < 4)) return 255; len = 2; fid->i32.ino = inode->i_ino; fid->i32.gen = inode->i_generation; if (connectable && !S_ISDIR(inode->i_mode)) { struct inode *parent; spin_lock(&dentry->d_lock); parent = dentry->d_parent->d_inode; fid->i32.parent_ino = parent->i_ino; fid->i32.parent_gen = parent->i_generation; spin_unlock(&dentry->d_lock); len = 4; type = FILEID_INO32_GEN_PARENT; } *max_len = len; return type; } int exportfs_encode_fh(struct dentry *dentry, struct fid *fid, int *max_len, int connectable) { const struct export_operations *nop = dentry->d_sb->s_export_op; int error; if (nop->encode_fh) error = nop->encode_fh(dentry, fid->raw, max_len, connectable); else error = export_encode_fh(dentry, fid, max_len, connectable); return error; } EXPORT_SYMBOL_GPL(exportfs_encode_fh); struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid, int fh_len, int fileid_type, int (*acceptable)(void *, struct dentry *), void *context) { const struct export_operations *nop = mnt->mnt_sb->s_export_op; struct dentry *result, *alias; char nbuf[NAME_MAX+1]; int err; /* * Try to get any dentry for the given file handle from the filesystem. */ result = nop->fh_to_dentry(mnt->mnt_sb, fid, fh_len, fileid_type); if (!result) result = ERR_PTR(-ESTALE); if (IS_ERR(result)) return result; if (S_ISDIR(result->d_inode->i_mode)) { /* * This request is for a directory. * * On the positive side there is only one dentry for each * directory inode. On the negative side this implies that we * to ensure our dentry is connected all the way up to the * filesystem root. */ if (result->d_flags & DCACHE_DISCONNECTED) { err = reconnect_path(mnt, result, nbuf); if (err) goto err_result; } if (!acceptable(context, result)) { err = -EACCES; goto err_result; } return result; } else { /* * It's not a directory. Life is a little more complicated. */ struct dentry *target_dir, *nresult; /* * See if either the dentry we just got from the filesystem * or any alias for it is acceptable. This is always true * if this filesystem is exported without the subtreecheck * option. If the filesystem is exported with the subtree * check option there's a fair chance we need to look at * the parent directory in the file handle and make sure * it's connected to the filesystem root. */ alias = find_acceptable_alias(result, acceptable, context); if (alias) return alias; /* * Try to extract a dentry for the parent directory from the * file handle. If this fails we'll have to give up. */ err = -ESTALE; if (!nop->fh_to_parent) goto err_result; target_dir = nop->fh_to_parent(mnt->mnt_sb, fid, fh_len, fileid_type); if (!target_dir) goto err_result; err = PTR_ERR(target_dir); if (IS_ERR(target_dir)) goto err_result; /* * And as usual we need to make sure the parent directory is * connected to the filesystem root. The VFS really doesn't * like disconnected directories.. */ err = reconnect_path(mnt, target_dir, nbuf); if (err) { dput(target_dir); goto err_result; } /* * Now that we've got both a well-connected parent and a * dentry for the inode we're after, make sure that our * inode is actually connected to the parent. */ err = exportfs_get_name(mnt, target_dir, nbuf, result); if (!err) { mutex_lock(&target_dir->d_inode->i_mutex); nresult = lookup_one_len(nbuf, target_dir, strlen(nbuf)); mutex_unlock(&target_dir->d_inode->i_mutex); if (!IS_ERR(nresult)) { if (nresult->d_inode) { dput(result); result = nresult; } else dput(nresult); } } /* * At this point we are done with the parent, but it's pinned * by the child dentry anyway. */ dput(target_dir); /* * And finally make sure the dentry is actually acceptable * to NFSD. */ alias = find_acceptable_alias(result, acceptable, context); if (!alias) { err = -EACCES; goto err_result; } return alias; } err_result: dput(result); return ERR_PTR(err); } EXPORT_SYMBOL_GPL(exportfs_decode_fh); MODULE_LICENSE("GPL");