diff options
| -rw-r--r-- | fs/namei.c | 182 | ||||
| -rw-r--r-- | fs/namespace.c | 2 | ||||
| -rw-r--r-- | include/linux/namei.h | 1 |
3 files changed, 184 insertions, 1 deletions
diff --git a/fs/namei.c b/fs/namei.c index 89a612e392eb..b234e4ec0a71 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -2184,6 +2184,188 @@ user_path_parent(int dfd, const char __user *path, struct nameidata *nd, return s; } +/** + * umount_lookup_last - look up last component for umount + * @nd: pathwalk nameidata - currently pointing at parent directory of "last" + * @path: pointer to container for result + * + * This is a special lookup_last function just for umount. In this case, we + * need to resolve the path without doing any revalidation. + * + * The nameidata should be the result of doing a LOOKUP_PARENT pathwalk. Since + * mountpoints are always pinned in the dcache, their ancestors are too. Thus, + * in almost all cases, this lookup will be served out of the dcache. The only + * cases where it won't are if nd->last refers to a symlink or the path is + * bogus and it doesn't exist. + * + * Returns: + * -error: if there was an error during lookup. This includes -ENOENT if the + * lookup found a negative dentry. The nd->path reference will also be + * put in this case. + * + * 0: if we successfully resolved nd->path and found it to not to be a + * symlink that needs to be followed. "path" will also be populated. + * The nd->path reference will also be put. + * + * 1: if we successfully resolved nd->last and found it to be a symlink + * that needs to be followed. "path" will be populated with the path + * to the link, and nd->path will *not* be put. + */ +static int +umount_lookup_last(struct nameidata *nd, struct path *path) +{ + int error = 0; + struct dentry *dentry; + struct dentry *dir = nd->path.dentry; + + if (unlikely(nd->flags & LOOKUP_RCU)) { + WARN_ON_ONCE(1); + error = -ECHILD; + goto error_check; + } + + nd->flags &= ~LOOKUP_PARENT; + + if (unlikely(nd->last_type != LAST_NORM)) { + error = handle_dots(nd, nd->last_type); + if (!error) + dentry = dget(nd->path.dentry); + goto error_check; + } + + mutex_lock(&dir->d_inode->i_mutex); + dentry = d_lookup(dir, &nd->last); + if (!dentry) { + /* + * No cached dentry. Mounted dentries are pinned in the cache, + * so that means that this dentry is probably a symlink or the + * path doesn't actually point to a mounted dentry. + */ + dentry = d_alloc(dir, &nd->last); + if (!dentry) { + error = -ENOMEM; + } else { + dentry = lookup_real(dir->d_inode, dentry, nd->flags); + if (IS_ERR(dentry)) + error = PTR_ERR(dentry); + } + } + mutex_unlock(&dir->d_inode->i_mutex); + +error_check: + if (!error) { + if (!dentry->d_inode) { + error = -ENOENT; + dput(dentry); + } else { + path->dentry = dentry; + path->mnt = mntget(nd->path.mnt); + if (should_follow_link(dentry->d_inode, + nd->flags & LOOKUP_FOLLOW)) + return 1; + follow_mount(path); + } + } + terminate_walk(nd); + return error; +} + +/** + * path_umountat - look up a path to be umounted + * @dfd: directory file descriptor to start walk from + * @name: full pathname to walk + * @flags: lookup flags + * @nd: pathwalk nameidata + * + * Look up the given name, but don't attempt to revalidate the last component. + * Returns 0 and "path" will be valid on success; Retuns error otherwise. + */ +static int +path_umountat(int dfd, const char *name, struct path *path, unsigned int flags) +{ + struct file *base = NULL; + struct nameidata nd; + int err; + + err = path_init(dfd, name, flags | LOOKUP_PARENT, &nd, &base); + if (unlikely(err)) + return err; + + current->total_link_count = 0; + err = link_path_walk(name, &nd); + if (err) + goto out; + + /* If we're in rcuwalk, drop out of it to handle last component */ + if (nd.flags & LOOKUP_RCU) { + err = unlazy_walk(&nd, NULL); + if (err) { + terminate_walk(&nd); + goto out; + } + } + + err = umount_lookup_last(&nd, path); + while (err > 0) { + void *cookie; + struct path link = *path; + err = may_follow_link(&link, &nd); + if (unlikely(err)) + break; + nd.flags |= LOOKUP_PARENT; + err = follow_link(&link, &nd, &cookie); + if (err) + break; + err = umount_lookup_last(&nd, path); + put_link(&nd, &link, cookie); + } +out: + if (base) + fput(base); + + if (nd.root.mnt && !(nd.flags & LOOKUP_ROOT)) + path_put(&nd.root); + + return err; +} + +/** + * user_path_umountat - lookup a path from userland in order to umount it + * @dfd: directory file descriptor + * @name: pathname from userland + * @flags: lookup flags + * @path: pointer to container to hold result + * + * A umount is a special case for path walking. We're not actually interested + * in the inode in this situation, and ESTALE errors can be a problem. We + * simply want track down the dentry and vfsmount attached at the mountpoint + * and avoid revalidating the last component. + * + * Returns 0 and populates "path" on success. + */ +int +user_path_umountat(int dfd, const char __user *name, unsigned int flags, + struct path *path) +{ + struct filename *s = getname(name); + int error; + + if (IS_ERR(s)) + return PTR_ERR(s); + + error = path_umountat(dfd, s->name, path, flags | LOOKUP_RCU); + if (unlikely(error == -ECHILD)) + error = path_umountat(dfd, s->name, path, flags); + if (unlikely(error == -ESTALE)) + error = path_umountat(dfd, s->name, path, flags | LOOKUP_REVAL); + + if (likely(!error)) + audit_inode(s, path->dentry, 0); + + putname(s); + return error; +} + /* * It's inline, so penalty for filesystems that don't use sticky bit is * minimal. diff --git a/fs/namespace.c b/fs/namespace.c index a45ba4f267fe..ad8ea9bc2518 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1318,7 +1318,7 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags) if (!(flags & UMOUNT_NOFOLLOW)) lookup_flags |= LOOKUP_FOLLOW; - retval = user_path_at(AT_FDCWD, name, lookup_flags, &path); + retval = user_path_umountat(AT_FDCWD, name, lookup_flags, &path); if (retval) goto out; mnt = real_mount(path.mnt); diff --git a/include/linux/namei.h b/include/linux/namei.h index 5a5ff57ceed4..cd09751c71a0 100644 --- a/include/linux/namei.h +++ b/include/linux/namei.h @@ -58,6 +58,7 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND}; extern int user_path_at(int, const char __user *, unsigned, struct path *); extern int user_path_at_empty(int, const char __user *, unsigned, struct path *, int *empty); +extern int user_path_umountat(int, const char __user *, unsigned int, struct path *); #define user_path(name, path) user_path_at(AT_FDCWD, name, LOOKUP_FOLLOW, path) #define user_lpath(name, path) user_path_at(AT_FDCWD, name, 0, path) |