/* * dcookies.c * * Copyright 2002 John Levon <levon@movementarian.org> * * Persistent cookie-path mappings. These are used by * profilers to convert a per-task EIP value into something * non-transitory that can be processed at a later date. * This is done by locking the dentry/vfsmnt pair in the * kernel until released by the tasks needing the persistent * objects. The tag is simply an unsigned long that refers * to the pair and can be looked up from userspace. */ #include <linux/config.h> #include <linux/syscalls.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/list.h> #include <linux/mount.h> #include <linux/capability.h> #include <linux/dcache.h> #include <linux/mm.h> #include <linux/errno.h> #include <linux/dcookies.h> #include <linux/mutex.h> #include <asm/uaccess.h> /* The dcookies are allocated from a kmem_cache and * hashed onto a small number of lists. None of the * code here is particularly performance critical */ struct dcookie_struct { struct dentry * dentry; struct vfsmount * vfsmnt; struct list_head hash_list; }; static LIST_HEAD(dcookie_users); static DEFINE_MUTEX(dcookie_mutex); static kmem_cache_t *dcookie_cache __read_mostly; static struct list_head *dcookie_hashtable __read_mostly; static size_t hash_size __read_mostly; static inline int is_live(void) { return !(list_empty(&dcookie_users)); } /* The dentry is locked, its address will do for the cookie */ static inline unsigned long dcookie_value(struct dcookie_struct * dcs) { return (unsigned long)dcs->dentry; } static size_t dcookie_hash(unsigned long dcookie) { return (dcookie >> L1_CACHE_SHIFT) & (hash_size - 1); } static struct dcookie_struct * find_dcookie(unsigned long dcookie) { struct dcookie_struct *found = NULL; struct dcookie_struct * dcs; struct list_head * pos; struct list_head * list; list = dcookie_hashtable + dcookie_hash(dcookie); list_for_each(pos, list) { dcs = list_entry(pos, struct dcookie_struct, hash_list); if (dcookie_value(dcs) == dcookie) { found = dcs; break; } } return found; } static void hash_dcookie(struct dcookie_struct * dcs) { struct list_head * list = dcookie_hashtable + dcookie_hash(dcookie_value(dcs)); list_add(&dcs->hash_list, list); } static struct dcookie_struct * alloc_dcookie(struct dentry * dentry, struct vfsmount * vfsmnt) { struct dcookie_struct * dcs = kmem_cache_alloc(dcookie_cache, GFP_KERNEL); if (!dcs) return NULL; dentry->d_cookie = dcs; dcs->dentry = dget(dentry); dcs->vfsmnt = mntget(vfsmnt); hash_dcookie(dcs); return dcs; } /* This is the main kernel-side routine that retrieves the cookie * value for a dentry/vfsmnt pair. */ int get_dcookie(struct dentry * dentry, struct vfsmount * vfsmnt, unsigned long * cookie) { int err = 0; struct dcookie_struct * dcs; mutex_lock(&dcookie_mutex); if (!is_live()) { err = -EINVAL; goto out; } dcs = dentry->d_cookie; if (!dcs) dcs = alloc_dcookie(dentry, vfsmnt); if (!dcs) { err = -ENOMEM; goto out; } *cookie = dcookie_value(dcs); out: mutex_unlock(&dcookie_mutex); return err; } /* And here is where the userspace process can look up the cookie value * to retrieve the path. */ asmlinkage long sys_lookup_dcookie(u64 cookie64, char __user * buf, size_t len) { unsigned long cookie = (unsigned long)cookie64; int err = -EINVAL; char * kbuf; char * path; size_t pathlen; struct dcookie_struct * dcs; /* we could leak path information to users * without dir read permission without this */ if (!capable(CAP_SYS_ADMIN)) return -EPERM; mutex_lock(&dcookie_mutex); if (!is_live()) { err = -EINVAL; goto out; } if (!(dcs = find_dcookie(cookie))) goto out; err = -ENOMEM; kbuf = kmalloc(PAGE_SIZE, GFP_KERNEL); if (!kbuf) goto out; /* FIXME: (deleted) ? */ path = d_path(dcs->dentry, dcs->vfsmnt, kbuf, PAGE_SIZE); if (IS_ERR(path)) { err = PTR_ERR(path); goto out_free; } err = -ERANGE; pathlen = kbuf + PAGE_SIZE - path; if (pathlen <= len) { err = pathlen; if (copy_to_user(buf, path, pathlen)) err = -EFAULT; } out_free: kfree(kbuf); out: mutex_unlock(&dcookie_mutex); return err; } static int dcookie_init(void) { struct list_head * d; unsigned int i, hash_bits; int err = -ENOMEM; dcookie_cache = kmem_cache_create("dcookie_cache", sizeof(struct dcookie_struct), 0, 0, NULL, NULL); if (!dcookie_cache) goto out; dcookie_hashtable = kmalloc(PAGE_SIZE, GFP_KERNEL); if (!dcookie_hashtable) goto out_kmem; err = 0; /* * Find the power-of-two list-heads that can fit into the allocation.. * We don't guarantee that "sizeof(struct list_head)" is necessarily * a power-of-two. */ hash_size = PAGE_SIZE / sizeof(struct list_head); hash_bits = 0; do { hash_bits++; } while ((hash_size >> hash_bits) != 0); hash_bits--; /* * Re-calculate the actual number of entries and the mask * from the number of bits we can fit. */ hash_size = 1UL << hash_bits; /* And initialize the newly allocated array */ d = dcookie_hashtable; i = hash_size; do { INIT_LIST_HEAD(d); d++; i--; } while (i); out: return err; out_kmem: kmem_cache_destroy(dcookie_cache); goto out; } static void free_dcookie(struct dcookie_struct * dcs) { dcs->dentry->d_cookie = NULL; dput(dcs->dentry); mntput(dcs->vfsmnt); kmem_cache_free(dcookie_cache, dcs); } static void dcookie_exit(void) { struct list_head * list; struct list_head * pos; struct list_head * pos2; struct dcookie_struct * dcs; size_t i; for (i = 0; i < hash_size; ++i) { list = dcookie_hashtable + i; list_for_each_safe(pos, pos2, list) { dcs = list_entry(pos, struct dcookie_struct, hash_list); list_del(&dcs->hash_list); free_dcookie(dcs); } } kfree(dcookie_hashtable); kmem_cache_destroy(dcookie_cache); } struct dcookie_user { struct list_head next; }; struct dcookie_user * dcookie_register(void) { struct dcookie_user * user; mutex_lock(&dcookie_mutex); user = kmalloc(sizeof(struct dcookie_user), GFP_KERNEL); if (!user) goto out; if (!is_live() && dcookie_init()) goto out_free; list_add(&user->next, &dcookie_users); out: mutex_unlock(&dcookie_mutex); return user; out_free: kfree(user); user = NULL; goto out; } void dcookie_unregister(struct dcookie_user * user) { mutex_lock(&dcookie_mutex); list_del(&user->next); kfree(user); if (!is_live()) dcookie_exit(); mutex_unlock(&dcookie_mutex); } EXPORT_SYMBOL_GPL(dcookie_register); EXPORT_SYMBOL_GPL(dcookie_unregister); EXPORT_SYMBOL_GPL(get_dcookie);