cregit-Linux how code gets into the kernel

Release 4.10 fs/dcookies.c

Directory: fs
 * dcookies.c
 * Copyright 2002 John Levon <>
 * 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/syscalls.h>
#include <linux/export.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/err.h>
#include <linux/errno.h>
#include <linux/dcookies.h>
#include <linux/mutex.h>
#include <linux/path.h>
#include <linux/compat.h>
#include <linux/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 path path;
struct list_head hash_list;

static LIST_HEAD(dcookie_users);
static DEFINE_MUTEX(dcookie_mutex);

static struct kmem_cache *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)); }


john levonjohn levon19100.00%1100.00%

/* 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->path.dentry; }


john levonjohn levon2291.67%266.67%
jan blunckjan blunck28.33%133.33%

static size_t dcookie_hash(unsigned long dcookie) { return (dcookie >> L1_CACHE_SHIFT) & (hash_size - 1); }


john levonjohn levon23100.00%2100.00%

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; }


john levonjohn levon8198.78%266.67%
mika kukkonenmika kukkonen11.22%133.33%

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); }


john levonjohn levon36100.00%1100.00%

static struct dcookie_struct *alloc_dcookie(const struct path *path) { struct dcookie_struct *dcs = kmem_cache_alloc(dcookie_cache, GFP_KERNEL); struct dentry *d; if (!dcs) return NULL; d = path->dentry; spin_lock(&d->d_lock); d->d_flags |= DCACHE_COOKIE; spin_unlock(&d->d_lock); dcs->path = *path; path_get(path); hash_dcookie(dcs); return dcs; }


john levonjohn levon4754.02%120.00%
nick pigginnick piggin2832.18%120.00%
jan blunckjan blunck910.34%120.00%
miklos szeredimiklos szeredi22.30%120.00%
al viroal viro11.15%120.00%

/* This is the main kernel-side routine that retrieves the cookie * value for a dentry/vfsmnt pair. */
int get_dcookie(const struct path *path, unsigned long *cookie) { int err = 0; struct dcookie_struct * dcs; mutex_lock(&dcookie_mutex); if (!is_live()) { err = -EINVAL; goto out; } if (path->dentry->d_flags & DCACHE_COOKIE) { dcs = find_dcookie((unsigned long)path->dentry); } else { dcs = alloc_dcookie(path); if (!dcs) { err = -ENOMEM; goto out; } } *cookie = dcookie_value(dcs); out: mutex_unlock(&dcookie_mutex); return err; }


john levonjohn levon8572.65%233.33%
nick pigginnick piggin2218.80%116.67%
jan blunckjan blunck54.27%116.67%
ingo molnaringo molnar43.42%116.67%
al viroal viro10.85%116.67%

/* And here is where the userspace process can look up the cookie value * to retrieve the path. */ SYSCALL_DEFINE3(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->path, kbuf, PAGE_SIZE); mutex_unlock(&dcookie_mutex); 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); return err; out: mutex_unlock(&dcookie_mutex); return err; } #ifdef CONFIG_COMPAT COMPAT_SYSCALL_DEFINE4(lookup_dcookie, u32, w0, u32, w1, char __user *, buf, compat_size_t, len) { #ifdef __BIG_ENDIAN return sys_lookup_dcookie(((u64)w0 << 32) | w1, buf, len); #else return sys_lookup_dcookie(((u64)w1 << 32) | w0, buf, len); #endif } #endif
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); 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; }


john levonjohn levon158100.00%1100.00%

static void free_dcookie(struct dcookie_struct * dcs) { struct dentry *d = dcs->path.dentry; spin_lock(&d->d_lock); d->d_flags &= ~DCACHE_COOKIE; spin_unlock(&d->d_lock); path_put(&dcs->path); kmem_cache_free(dcookie_cache, dcs); }


john levonjohn levon2846.67%133.33%
nick pigginnick piggin2745.00%133.33%
jan blunckjan blunck58.33%133.33%

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); }


john levonjohn levon97100.00%1100.00%

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; }


john levonjohn levon8595.51%150.00%
ingo molnaringo molnar44.49%150.00%

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); }


john levonjohn levon4090.91%150.00%
ingo molnaringo molnar49.09%150.00%

EXPORT_SYMBOL_GPL(dcookie_register); EXPORT_SYMBOL_GPL(dcookie_unregister); EXPORT_SYMBOL_GPL(get_dcookie);

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ingo molnaringo molnar211.68%14.76%
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Directory: fs
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