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356 lines
7.1 KiB
356 lines
7.1 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* |
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* dcookies.c |
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* |
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* Copyright 2002 John Levon <[email protected]> |
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* |
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* Persistent cookie-path mappings. These are used by |
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* profilers to convert a per-task EIP value into something |
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* non-transitory that can be processed at a later date. |
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* This is done by locking the dentry/vfsmnt pair in the |
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* kernel until released by the tasks needing the persistent |
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* objects. The tag is simply an unsigned long that refers |
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* to the pair and can be looked up from userspace. |
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*/ |
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#include <linux/syscalls.h> |
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#include <linux/export.h> |
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#include <linux/slab.h> |
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#include <linux/list.h> |
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#include <linux/mount.h> |
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#include <linux/capability.h> |
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#include <linux/dcache.h> |
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#include <linux/mm.h> |
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#include <linux/err.h> |
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#include <linux/errno.h> |
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#include <linux/dcookies.h> |
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#include <linux/mutex.h> |
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#include <linux/path.h> |
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#include <linux/compat.h> |
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#include <linux/uaccess.h> |
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/* The dcookies are allocated from a kmem_cache and |
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* hashed onto a small number of lists. None of the |
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* code here is particularly performance critical |
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*/ |
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struct dcookie_struct { |
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struct path path; |
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struct list_head hash_list; |
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}; |
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static LIST_HEAD(dcookie_users); |
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static DEFINE_MUTEX(dcookie_mutex); |
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static struct kmem_cache *dcookie_cache __read_mostly; |
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static struct list_head *dcookie_hashtable __read_mostly; |
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static size_t hash_size __read_mostly; |
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static inline int is_live(void) |
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{ |
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return !(list_empty(&dcookie_users)); |
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} |
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/* The dentry is locked, its address will do for the cookie */ |
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static inline unsigned long dcookie_value(struct dcookie_struct * dcs) |
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{ |
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return (unsigned long)dcs->path.dentry; |
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} |
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static size_t dcookie_hash(unsigned long dcookie) |
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{ |
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return (dcookie >> L1_CACHE_SHIFT) & (hash_size - 1); |
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} |
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static struct dcookie_struct * find_dcookie(unsigned long dcookie) |
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{ |
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struct dcookie_struct *found = NULL; |
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struct dcookie_struct * dcs; |
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struct list_head * pos; |
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struct list_head * list; |
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list = dcookie_hashtable + dcookie_hash(dcookie); |
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list_for_each(pos, list) { |
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dcs = list_entry(pos, struct dcookie_struct, hash_list); |
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if (dcookie_value(dcs) == dcookie) { |
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found = dcs; |
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break; |
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} |
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} |
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return found; |
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} |
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static void hash_dcookie(struct dcookie_struct * dcs) |
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{ |
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struct list_head * list = dcookie_hashtable + dcookie_hash(dcookie_value(dcs)); |
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list_add(&dcs->hash_list, list); |
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} |
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static struct dcookie_struct *alloc_dcookie(const struct path *path) |
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{ |
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struct dcookie_struct *dcs = kmem_cache_alloc(dcookie_cache, |
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GFP_KERNEL); |
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struct dentry *d; |
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if (!dcs) |
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return NULL; |
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d = path->dentry; |
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spin_lock(&d->d_lock); |
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d->d_flags |= DCACHE_COOKIE; |
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spin_unlock(&d->d_lock); |
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dcs->path = *path; |
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path_get(path); |
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hash_dcookie(dcs); |
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return dcs; |
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} |
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/* This is the main kernel-side routine that retrieves the cookie |
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* value for a dentry/vfsmnt pair. |
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*/ |
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int get_dcookie(const struct path *path, unsigned long *cookie) |
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{ |
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int err = 0; |
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struct dcookie_struct * dcs; |
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mutex_lock(&dcookie_mutex); |
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if (!is_live()) { |
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err = -EINVAL; |
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goto out; |
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} |
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if (path->dentry->d_flags & DCACHE_COOKIE) { |
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dcs = find_dcookie((unsigned long)path->dentry); |
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} else { |
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dcs = alloc_dcookie(path); |
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if (!dcs) { |
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err = -ENOMEM; |
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goto out; |
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} |
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} |
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*cookie = dcookie_value(dcs); |
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out: |
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mutex_unlock(&dcookie_mutex); |
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return err; |
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} |
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/* And here is where the userspace process can look up the cookie value |
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* to retrieve the path. |
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*/ |
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static int do_lookup_dcookie(u64 cookie64, char __user *buf, size_t len) |
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{ |
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unsigned long cookie = (unsigned long)cookie64; |
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int err = -EINVAL; |
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char * kbuf; |
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char * path; |
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size_t pathlen; |
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struct dcookie_struct * dcs; |
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/* we could leak path information to users |
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* without dir read permission without this |
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*/ |
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if (!capable(CAP_SYS_ADMIN)) |
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return -EPERM; |
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mutex_lock(&dcookie_mutex); |
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if (!is_live()) { |
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err = -EINVAL; |
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goto out; |
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} |
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if (!(dcs = find_dcookie(cookie))) |
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goto out; |
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err = -ENOMEM; |
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kbuf = kmalloc(PAGE_SIZE, GFP_KERNEL); |
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if (!kbuf) |
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goto out; |
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/* FIXME: (deleted) ? */ |
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path = d_path(&dcs->path, kbuf, PAGE_SIZE); |
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mutex_unlock(&dcookie_mutex); |
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if (IS_ERR(path)) { |
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err = PTR_ERR(path); |
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goto out_free; |
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} |
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err = -ERANGE; |
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pathlen = kbuf + PAGE_SIZE - path; |
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if (pathlen <= len) { |
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err = pathlen; |
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if (copy_to_user(buf, path, pathlen)) |
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err = -EFAULT; |
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} |
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out_free: |
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kfree(kbuf); |
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return err; |
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out: |
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mutex_unlock(&dcookie_mutex); |
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return err; |
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} |
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SYSCALL_DEFINE3(lookup_dcookie, u64, cookie64, char __user *, buf, size_t, len) |
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{ |
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return do_lookup_dcookie(cookie64, buf, len); |
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} |
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#ifdef CONFIG_COMPAT |
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COMPAT_SYSCALL_DEFINE4(lookup_dcookie, u32, w0, u32, w1, char __user *, buf, compat_size_t, len) |
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{ |
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#ifdef __BIG_ENDIAN |
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return do_lookup_dcookie(((u64)w0 << 32) | w1, buf, len); |
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#else |
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return do_lookup_dcookie(((u64)w1 << 32) | w0, buf, len); |
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#endif |
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} |
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#endif |
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static int dcookie_init(void) |
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{ |
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struct list_head * d; |
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unsigned int i, hash_bits; |
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int err = -ENOMEM; |
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dcookie_cache = kmem_cache_create("dcookie_cache", |
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sizeof(struct dcookie_struct), |
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0, 0, NULL); |
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if (!dcookie_cache) |
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goto out; |
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dcookie_hashtable = kmalloc(PAGE_SIZE, GFP_KERNEL); |
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if (!dcookie_hashtable) |
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goto out_kmem; |
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err = 0; |
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/* |
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* Find the power-of-two list-heads that can fit into the allocation.. |
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* We don't guarantee that "sizeof(struct list_head)" is necessarily |
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* a power-of-two. |
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*/ |
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hash_size = PAGE_SIZE / sizeof(struct list_head); |
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hash_bits = 0; |
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do { |
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hash_bits++; |
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} while ((hash_size >> hash_bits) != 0); |
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hash_bits--; |
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/* |
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* Re-calculate the actual number of entries and the mask |
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* from the number of bits we can fit. |
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*/ |
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hash_size = 1UL << hash_bits; |
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/* And initialize the newly allocated array */ |
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d = dcookie_hashtable; |
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i = hash_size; |
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do { |
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INIT_LIST_HEAD(d); |
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d++; |
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i--; |
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} while (i); |
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out: |
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return err; |
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out_kmem: |
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kmem_cache_destroy(dcookie_cache); |
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goto out; |
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} |
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static void free_dcookie(struct dcookie_struct * dcs) |
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{ |
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struct dentry *d = dcs->path.dentry; |
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spin_lock(&d->d_lock); |
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d->d_flags &= ~DCACHE_COOKIE; |
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spin_unlock(&d->d_lock); |
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path_put(&dcs->path); |
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kmem_cache_free(dcookie_cache, dcs); |
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} |
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static void dcookie_exit(void) |
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{ |
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struct list_head * list; |
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struct list_head * pos; |
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struct list_head * pos2; |
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struct dcookie_struct * dcs; |
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size_t i; |
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for (i = 0; i < hash_size; ++i) { |
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list = dcookie_hashtable + i; |
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list_for_each_safe(pos, pos2, list) { |
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dcs = list_entry(pos, struct dcookie_struct, hash_list); |
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list_del(&dcs->hash_list); |
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free_dcookie(dcs); |
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} |
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} |
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kfree(dcookie_hashtable); |
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kmem_cache_destroy(dcookie_cache); |
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} |
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struct dcookie_user { |
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struct list_head next; |
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}; |
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struct dcookie_user * dcookie_register(void) |
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{ |
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struct dcookie_user * user; |
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mutex_lock(&dcookie_mutex); |
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user = kmalloc(sizeof(struct dcookie_user), GFP_KERNEL); |
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if (!user) |
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goto out; |
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if (!is_live() && dcookie_init()) |
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goto out_free; |
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list_add(&user->next, &dcookie_users); |
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out: |
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mutex_unlock(&dcookie_mutex); |
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return user; |
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out_free: |
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kfree(user); |
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user = NULL; |
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goto out; |
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} |
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void dcookie_unregister(struct dcookie_user * user) |
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{ |
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mutex_lock(&dcookie_mutex); |
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list_del(&user->next); |
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kfree(user); |
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if (!is_live()) |
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dcookie_exit(); |
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mutex_unlock(&dcookie_mutex); |
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} |
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EXPORT_SYMBOL_GPL(dcookie_register); |
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EXPORT_SYMBOL_GPL(dcookie_unregister); |
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EXPORT_SYMBOL_GPL(get_dcookie);
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