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![Linus Torvalds](/assets/img/avatar_default.png)
Pull vfs d_inode/d_flags memory ordering fixes from Al Viro: "Fallout from tree-wide audit for ->d_inode/->d_flags barriers use. Basically, the problem is that negative pinned dentries require careful treatment - unless ->d_lock is locked or parent is held at least shared, another thread can make them positive right under us. Most of the uses turned out to be safe - the main surprises as far as filesystems are concerned were - race in dget_parent() fastpath, that might end up with the caller observing the returned dentry _negative_, due to insufficient barriers. It is positive in memory, but we could end up seeing the wrong value of ->d_inode in CPU cache. Fixed. - manual checks that result of lookup_one_len_unlocked() is positive (and rejection of negatives). Again, insufficient barriers (we might end up with inconsistent observed values of ->d_inode and ->d_flags). Fixed by switching to a new primitive that does the checks itself and returns ERR_PTR(-ENOENT) instead of a negative dentry. That way we get rid of boilerplate converting negatives into ERR_PTR(-ENOENT) in the callers and have a single place to deal with the barrier-related mess - inside fs/namei.c rather than in every caller out there. The guts of pathname resolution *do* need to be careful - the race found by Ritesh is real, as well as several similar races. Fortunately, it turns out that we can take care of that with fairly local changes in there. The tree-wide audit had not been fun, and I hate the idea of repeating it. I think the right approach would be to annotate the places where we are _not_ guaranteed ->d_inode/->d_flags stability and have sparse catch regressions. But I'm still not sure what would be the least invasive way of doing that and it's clearly the next cycle fodder" * 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: fs/namei.c: fix missing barriers when checking positivity fix dget_parent() fastpath race new helper: lookup_positive_unlocked() fs/namei.c: pull positivity check into follow_managed()
397 lines
9.6 KiB
C
397 lines
9.6 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* fs/kernfs/mount.c - kernfs mount implementation
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*
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* Copyright (c) 2001-3 Patrick Mochel
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* Copyright (c) 2007 SUSE Linux Products GmbH
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* Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
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*/
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#include <linux/fs.h>
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#include <linux/mount.h>
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#include <linux/init.h>
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#include <linux/magic.h>
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#include <linux/slab.h>
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#include <linux/pagemap.h>
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#include <linux/namei.h>
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#include <linux/seq_file.h>
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#include <linux/exportfs.h>
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#include "kernfs-internal.h"
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struct kmem_cache *kernfs_node_cache, *kernfs_iattrs_cache;
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static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
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{
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struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));
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struct kernfs_syscall_ops *scops = root->syscall_ops;
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if (scops && scops->show_options)
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return scops->show_options(sf, root);
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return 0;
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}
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static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
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{
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struct kernfs_node *node = kernfs_dentry_node(dentry);
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struct kernfs_root *root = kernfs_root(node);
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struct kernfs_syscall_ops *scops = root->syscall_ops;
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if (scops && scops->show_path)
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return scops->show_path(sf, node, root);
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seq_dentry(sf, dentry, " \t\n\\");
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return 0;
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}
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const struct super_operations kernfs_sops = {
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.statfs = simple_statfs,
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.drop_inode = generic_delete_inode,
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.evict_inode = kernfs_evict_inode,
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.show_options = kernfs_sop_show_options,
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.show_path = kernfs_sop_show_path,
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};
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static int kernfs_encode_fh(struct inode *inode, __u32 *fh, int *max_len,
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struct inode *parent)
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{
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struct kernfs_node *kn = inode->i_private;
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if (*max_len < 2) {
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*max_len = 2;
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return FILEID_INVALID;
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}
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*max_len = 2;
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*(u64 *)fh = kn->id;
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return FILEID_KERNFS;
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}
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static struct dentry *__kernfs_fh_to_dentry(struct super_block *sb,
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struct fid *fid, int fh_len,
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int fh_type, bool get_parent)
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{
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struct kernfs_super_info *info = kernfs_info(sb);
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struct kernfs_node *kn;
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struct inode *inode;
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u64 id;
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if (fh_len < 2)
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return NULL;
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switch (fh_type) {
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case FILEID_KERNFS:
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id = *(u64 *)fid;
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break;
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case FILEID_INO32_GEN:
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case FILEID_INO32_GEN_PARENT:
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/*
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* blk_log_action() exposes "LOW32,HIGH32" pair without
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* type and userland can call us with generic fid
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* constructed from them. Combine it back to ID. See
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* blk_log_action().
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*/
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id = ((u64)fid->i32.gen << 32) | fid->i32.ino;
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break;
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default:
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return NULL;
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}
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kn = kernfs_find_and_get_node_by_id(info->root, id);
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if (!kn)
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return ERR_PTR(-ESTALE);
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if (get_parent) {
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struct kernfs_node *parent;
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parent = kernfs_get_parent(kn);
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kernfs_put(kn);
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kn = parent;
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if (!kn)
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return ERR_PTR(-ESTALE);
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}
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inode = kernfs_get_inode(sb, kn);
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kernfs_put(kn);
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if (!inode)
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return ERR_PTR(-ESTALE);
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return d_obtain_alias(inode);
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}
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static struct dentry *kernfs_fh_to_dentry(struct super_block *sb,
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struct fid *fid, int fh_len,
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int fh_type)
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{
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return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, false);
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}
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static struct dentry *kernfs_fh_to_parent(struct super_block *sb,
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struct fid *fid, int fh_len,
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int fh_type)
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{
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return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, true);
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}
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static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
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{
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struct kernfs_node *kn = kernfs_dentry_node(child);
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return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
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}
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static const struct export_operations kernfs_export_ops = {
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.encode_fh = kernfs_encode_fh,
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.fh_to_dentry = kernfs_fh_to_dentry,
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.fh_to_parent = kernfs_fh_to_parent,
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.get_parent = kernfs_get_parent_dentry,
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};
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/**
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* kernfs_root_from_sb - determine kernfs_root associated with a super_block
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* @sb: the super_block in question
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*
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* Return the kernfs_root associated with @sb. If @sb is not a kernfs one,
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* %NULL is returned.
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*/
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struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
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{
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if (sb->s_op == &kernfs_sops)
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return kernfs_info(sb)->root;
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return NULL;
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}
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/*
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* find the next ancestor in the path down to @child, where @parent was the
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* ancestor whose descendant we want to find.
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*
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* Say the path is /a/b/c/d. @child is d, @parent is NULL. We return the root
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* node. If @parent is b, then we return the node for c.
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* Passing in d as @parent is not ok.
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*/
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static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
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struct kernfs_node *parent)
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{
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if (child == parent) {
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pr_crit_once("BUG in find_next_ancestor: called with parent == child");
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return NULL;
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}
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while (child->parent != parent) {
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if (!child->parent)
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return NULL;
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child = child->parent;
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}
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return child;
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}
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/**
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* kernfs_node_dentry - get a dentry for the given kernfs_node
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* @kn: kernfs_node for which a dentry is needed
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* @sb: the kernfs super_block
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*/
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struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
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struct super_block *sb)
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{
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struct dentry *dentry;
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struct kernfs_node *knparent = NULL;
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BUG_ON(sb->s_op != &kernfs_sops);
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dentry = dget(sb->s_root);
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/* Check if this is the root kernfs_node */
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if (!kn->parent)
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return dentry;
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knparent = find_next_ancestor(kn, NULL);
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if (WARN_ON(!knparent)) {
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dput(dentry);
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return ERR_PTR(-EINVAL);
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}
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do {
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struct dentry *dtmp;
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struct kernfs_node *kntmp;
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if (kn == knparent)
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return dentry;
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kntmp = find_next_ancestor(kn, knparent);
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if (WARN_ON(!kntmp)) {
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dput(dentry);
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return ERR_PTR(-EINVAL);
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}
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dtmp = lookup_positive_unlocked(kntmp->name, dentry,
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strlen(kntmp->name));
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dput(dentry);
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if (IS_ERR(dtmp))
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return dtmp;
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knparent = kntmp;
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dentry = dtmp;
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} while (true);
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}
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static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
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{
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struct kernfs_super_info *info = kernfs_info(sb);
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struct inode *inode;
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struct dentry *root;
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info->sb = sb;
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/* Userspace would break if executables or devices appear on sysfs */
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sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
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sb->s_blocksize = PAGE_SIZE;
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sb->s_blocksize_bits = PAGE_SHIFT;
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sb->s_magic = kfc->magic;
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sb->s_op = &kernfs_sops;
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sb->s_xattr = kernfs_xattr_handlers;
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if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
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sb->s_export_op = &kernfs_export_ops;
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sb->s_time_gran = 1;
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/* sysfs dentries and inodes don't require IO to create */
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sb->s_shrink.seeks = 0;
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/* get root inode, initialize and unlock it */
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mutex_lock(&kernfs_mutex);
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inode = kernfs_get_inode(sb, info->root->kn);
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mutex_unlock(&kernfs_mutex);
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if (!inode) {
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pr_debug("kernfs: could not get root inode\n");
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return -ENOMEM;
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}
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/* instantiate and link root dentry */
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root = d_make_root(inode);
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if (!root) {
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pr_debug("%s: could not get root dentry!\n", __func__);
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return -ENOMEM;
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}
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sb->s_root = root;
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sb->s_d_op = &kernfs_dops;
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return 0;
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}
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static int kernfs_test_super(struct super_block *sb, struct fs_context *fc)
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{
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struct kernfs_super_info *sb_info = kernfs_info(sb);
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struct kernfs_super_info *info = fc->s_fs_info;
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return sb_info->root == info->root && sb_info->ns == info->ns;
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}
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static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
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{
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struct kernfs_fs_context *kfc = fc->fs_private;
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kfc->ns_tag = NULL;
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return set_anon_super_fc(sb, fc);
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}
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/**
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* kernfs_super_ns - determine the namespace tag of a kernfs super_block
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* @sb: super_block of interest
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*
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* Return the namespace tag associated with kernfs super_block @sb.
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*/
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const void *kernfs_super_ns(struct super_block *sb)
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{
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struct kernfs_super_info *info = kernfs_info(sb);
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return info->ns;
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}
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/**
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* kernfs_get_tree - kernfs filesystem access/retrieval helper
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* @fc: The filesystem context.
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*
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* This is to be called from each kernfs user's fs_context->ops->get_tree()
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* implementation, which should set the specified ->@fs_type and ->@flags, and
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* specify the hierarchy and namespace tag to mount via ->@root and ->@ns,
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* respectively.
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*/
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int kernfs_get_tree(struct fs_context *fc)
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{
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struct kernfs_fs_context *kfc = fc->fs_private;
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struct super_block *sb;
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struct kernfs_super_info *info;
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int error;
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info = kzalloc(sizeof(*info), GFP_KERNEL);
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if (!info)
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return -ENOMEM;
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info->root = kfc->root;
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info->ns = kfc->ns_tag;
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INIT_LIST_HEAD(&info->node);
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fc->s_fs_info = info;
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sb = sget_fc(fc, kernfs_test_super, kernfs_set_super);
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if (IS_ERR(sb))
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return PTR_ERR(sb);
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if (!sb->s_root) {
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struct kernfs_super_info *info = kernfs_info(sb);
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kfc->new_sb_created = true;
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error = kernfs_fill_super(sb, kfc);
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if (error) {
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deactivate_locked_super(sb);
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return error;
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}
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sb->s_flags |= SB_ACTIVE;
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mutex_lock(&kernfs_mutex);
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list_add(&info->node, &info->root->supers);
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mutex_unlock(&kernfs_mutex);
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}
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fc->root = dget(sb->s_root);
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return 0;
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}
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void kernfs_free_fs_context(struct fs_context *fc)
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{
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/* Note that we don't deal with kfc->ns_tag here. */
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kfree(fc->s_fs_info);
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fc->s_fs_info = NULL;
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}
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/**
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* kernfs_kill_sb - kill_sb for kernfs
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* @sb: super_block being killed
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*
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* This can be used directly for file_system_type->kill_sb(). If a kernfs
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* user needs extra cleanup, it can implement its own kill_sb() and call
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* this function at the end.
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*/
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void kernfs_kill_sb(struct super_block *sb)
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{
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struct kernfs_super_info *info = kernfs_info(sb);
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mutex_lock(&kernfs_mutex);
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list_del(&info->node);
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mutex_unlock(&kernfs_mutex);
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/*
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* Remove the superblock from fs_supers/s_instances
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* so we can't find it, before freeing kernfs_super_info.
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*/
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kill_anon_super(sb);
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kfree(info);
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}
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void __init kernfs_init(void)
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{
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kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
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sizeof(struct kernfs_node),
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0, SLAB_PANIC, NULL);
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/* Creates slab cache for kernfs inode attributes */
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kernfs_iattrs_cache = kmem_cache_create("kernfs_iattrs_cache",
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sizeof(struct kernfs_iattrs),
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0, SLAB_PANIC, NULL);
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}
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