(2006-08-06) rescue-bootcd

extra/linux-2.6.10/kernel/user.c

@@ -0,0 +1,188 @@
+/*
+ * The "user cache".
+ *
+ * (C) Copyright 1991-2000 Linus Torvalds
+ *
+ * We have a per-user structure to keep track of how many
+ * processes, files etc the user has claimed, in order to be
+ * able to have per-user limits for system resources. 
+ */
+
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/bitops.h>
+#include <linux/key.h>
+
+/*
+ * UID task count cache, to get fast user lookup in "alloc_uid"
+ * when changing user ID's (ie setuid() and friends).
+ */
+#define UIDHASH_BITS		8
+#define UIDHASH_SZ		(1 << UIDHASH_BITS)
+#define UIDHASH_MASK		(UIDHASH_SZ - 1)
+#define __uidhashfn(uid)	(((uid >> UIDHASH_BITS) + uid) & UIDHASH_MASK)
+#define uidhashentry(uid)	(uidhash_table + __uidhashfn((uid)))
+
+static kmem_cache_t *uid_cachep;
+static struct list_head uidhash_table[UIDHASH_SZ];
+static spinlock_t uidhash_lock = SPIN_LOCK_UNLOCKED;
+
+struct user_struct root_user = {
+	.__count	= ATOMIC_INIT(1),
+	.processes	= ATOMIC_INIT(1),
+	.files		= ATOMIC_INIT(0),
+	.sigpending	= ATOMIC_INIT(0),
+	.mq_bytes	= 0,
+	.locked_shm     = 0,
+#ifdef CONFIG_KEYS
+	.uid_keyring	= &root_user_keyring,
+	.session_keyring = &root_session_keyring,
+#endif
+};
+
+/*
+ * These routines must be called with the uidhash spinlock held!
+ */
+static inline void uid_hash_insert(struct user_struct *up, struct list_head *hashent)
+{
+	list_add(&up->uidhash_list, hashent);
+}
+
+static inline void uid_hash_remove(struct user_struct *up)
+{
+	list_del(&up->uidhash_list);
+}
+
+static inline struct user_struct *uid_hash_find(uid_t uid, struct list_head *hashent)
+{
+	struct list_head *up;
+
+	list_for_each(up, hashent) {
+		struct user_struct *user;
+
+		user = list_entry(up, struct user_struct, uidhash_list);
+
+		if(user->uid == uid) {
+			atomic_inc(&user->__count);
+			return user;
+		}
+	}
+
+	return NULL;
+}
+
+/*
+ * Locate the user_struct for the passed UID.  If found, take a ref on it.  The
+ * caller must undo that ref with free_uid().
+ *
+ * If the user_struct could not be found, return NULL.
+ */
+struct user_struct *find_user(uid_t uid)
+{
+	struct user_struct *ret;
+
+	spin_lock(&uidhash_lock);
+	ret = uid_hash_find(uid, uidhashentry(uid));
+	spin_unlock(&uidhash_lock);
+	return ret;
+}
+
+void free_uid(struct user_struct *up)
+{
+	if (up && atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
+		uid_hash_remove(up);
+		key_put(up->uid_keyring);
+		key_put(up->session_keyring);
+		kmem_cache_free(uid_cachep, up);
+		spin_unlock(&uidhash_lock);
+	}
+}
+
+struct user_struct * alloc_uid(uid_t uid)
+{
+	struct list_head *hashent = uidhashentry(uid);
+	struct user_struct *up;
+
+	spin_lock(&uidhash_lock);
+	up = uid_hash_find(uid, hashent);
+	spin_unlock(&uidhash_lock);
+
+	if (!up) {
+		struct user_struct *new;
+
+		new = kmem_cache_alloc(uid_cachep, SLAB_KERNEL);
+		if (!new)
+			return NULL;
+		new->uid = uid;
+		atomic_set(&new->__count, 1);
+		atomic_set(&new->processes, 0);
+		atomic_set(&new->files, 0);
+		atomic_set(&new->sigpending, 0);
+
+		new->mq_bytes = 0;
+		new->locked_shm = 0;
+
+		if (alloc_uid_keyring(new) < 0) {
+			kmem_cache_free(uid_cachep, new);
+			return NULL;
+		}
+
+		/*
+		 * Before adding this, check whether we raced
+		 * on adding the same user already..
+		 */
+		spin_lock(&uidhash_lock);
+		up = uid_hash_find(uid, hashent);
+		if (up) {
+			key_put(new->uid_keyring);
+			key_put(new->session_keyring);
+			kmem_cache_free(uid_cachep, new);
+		} else {
+			uid_hash_insert(new, hashent);
+			up = new;
+		}
+		spin_unlock(&uidhash_lock);
+
+	}
+	return up;
+}
+
+void switch_uid(struct user_struct *new_user)
+{
+	struct user_struct *old_user;
+
+	/* What if a process setreuid()'s and this brings the
+	 * new uid over his NPROC rlimit?  We can check this now
+	 * cheaply with the new uid cache, so if it matters
+	 * we should be checking for it.  -DaveM
+	 */
+	old_user = current->user;
+	atomic_inc(&new_user->processes);
+	atomic_dec(&old_user->processes);
+	switch_uid_keyring(new_user);
+	current->user = new_user;
+	free_uid(old_user);
+	suid_keys(current);
+}
+
+
+static int __init uid_cache_init(void)
+{
+	int n;
+
+	uid_cachep = kmem_cache_create("uid_cache", sizeof(struct user_struct),
+			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL, NULL);
+
+	for(n = 0; n < UIDHASH_SZ; ++n)
+		INIT_LIST_HEAD(uidhash_table + n);
+
+	/* Insert the root user immediately (init already runs as root) */
+	spin_lock(&uidhash_lock);
+	uid_hash_insert(&root_user, uidhashentry(0));
+	spin_unlock(&uidhash_lock);
+
+	return 0;
+}
+
+module_init(uid_cache_init);