1 files changed, 189 insertions, 0 deletions

diff --git a/kernel/user.c b/kernel/user.c
new file mode 100644
index 000000000000..734575d55769
--- /dev/null
+++ b/kernel/user.c
@@ -0,0 +1,189 @@
+/*
+ * 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 (CONFIG_BASE_SMALL ? 3 : 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 DEFINE_SPINLOCK(uidhash_lock);
+
+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);