cred.c

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/* Task credentials management - see Documentation/security/credentials.txt
 *
 * Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells ([email protected])
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */
#include <linux/export.h>
#include <linux/cred.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/key.h>
#include <linux/keyctl.h>
#include <linux/init_task.h>
#include <linux/security.h>
#include <linux/binfmts.h>
#include <linux/cn_proc.h>

#if 0
#define kdebug(FMT, ...) \
    printk("[%-5.5s%5u] "FMT"\n", current->comm, current->pid ,##__VA_ARGS__)
#else
#define kdebug(FMT, ...) \
    no_printk("[%-5.5s%5u] "FMT"\n", current->comm, current->pid ,##__VA_ARGS__)
#endif

static struct kmem_cache *cred_jar;

/*
 * The common credentials for the initial task's thread group
 */
#ifdef CONFIG_KEYS
static struct thread_group_cred init_tgcred = {
    .usage  = ATOMIC_INIT(2),
    .tgid   = 0,
    .lock   = __SPIN_LOCK_UNLOCKED(init_cred.tgcred.lock),
};
#endif

/*
 * The initial credentials for the initial task
 */
struct cred init_cred = {
    .usage          = ATOMIC_INIT(4),
#ifdef CONFIG_DEBUG_CREDENTIALS
    .subscribers        = ATOMIC_INIT(2),
    .magic          = CRED_MAGIC,
#endif
    .uid            = GLOBAL_ROOT_UID,
    .gid            = GLOBAL_ROOT_GID,
    .suid           = GLOBAL_ROOT_UID,
    .sgid           = GLOBAL_ROOT_GID,
    .euid           = GLOBAL_ROOT_UID,
    .egid           = GLOBAL_ROOT_GID,
    .fsuid          = GLOBAL_ROOT_UID,
    .fsgid          = GLOBAL_ROOT_GID,
    .securebits     = SECUREBITS_DEFAULT,
    .cap_inheritable    = CAP_EMPTY_SET,
    .cap_permitted      = CAP_FULL_SET,
    .cap_effective      = CAP_FULL_SET,
    .cap_bset       = CAP_FULL_SET,
    .user           = INIT_USER,
    .user_ns        = &init_user_ns,
    .group_info     = &init_groups,
#ifdef CONFIG_KEYS
    .tgcred         = &init_tgcred,
#endif
};

static inline void set_cred_subscribers(struct cred *cred, int n)
{
#ifdef CONFIG_DEBUG_CREDENTIALS
    atomic_set(&cred->subscribers, n);
#endif
}

static inline int read_cred_subscribers(const struct cred *cred)
{
#ifdef CONFIG_DEBUG_CREDENTIALS
    return atomic_read(&cred->subscribers);
#else
    return 0;
#endif
}

static inline void alter_cred_subscribers(const struct cred *_cred, int n)
{
#ifdef CONFIG_DEBUG_CREDENTIALS
    struct cred *cred = (struct cred *) _cred;

    atomic_add(n, &cred->subscribers);
#endif
}

/*
 * Dispose of the shared task group credentials
 */
#ifdef CONFIG_KEYS
static void release_tgcred_rcu(struct rcu_head *rcu)
{
    struct thread_group_cred *tgcred =
        container_of(rcu, struct thread_group_cred, rcu);

    BUG_ON(atomic_read(&tgcred->usage) != 0);

    key_put(tgcred->session_keyring);
    key_put(tgcred->process_keyring);
    kfree(tgcred);
}
#endif

/*
 * Release a set of thread group credentials.
 */
static void release_tgcred(struct cred *cred)
{
#ifdef CONFIG_KEYS
    struct thread_group_cred *tgcred = cred->tgcred;

    if (atomic_dec_and_test(&tgcred->usage))
        call_rcu(&tgcred->rcu, release_tgcred_rcu);
#endif
}

/*
 * The RCU callback to actually dispose of a set of credentials
 */
static void put_cred_rcu(struct rcu_head *rcu)
{
    struct cred *cred = container_of(rcu, struct cred, rcu);

    kdebug("put_cred_rcu(%p)", cred);

#ifdef CONFIG_DEBUG_CREDENTIALS
    if (cred->magic != CRED_MAGIC_DEAD ||
        atomic_read(&cred->usage) != 0 ||
        read_cred_subscribers(cred) != 0)
        panic("CRED: put_cred_rcu() sees %p with"
              " mag %x, put %p, usage %d, subscr %d\n",
              cred, cred->magic, cred->put_addr,
              atomic_read(&cred->usage),
              read_cred_subscribers(cred));
#else
    if (atomic_read(&cred->usage) != 0)
        panic("CRED: put_cred_rcu() sees %p with usage %d\n",
              cred, atomic_read(&cred->usage));
#endif

    security_cred_free(cred);
    key_put(cred->thread_keyring);
    key_put(cred->request_key_auth);
    release_tgcred(cred);
    if (cred->group_info)
        put_group_info(cred->group_info);
    free_uid(cred->user);
    put_user_ns(cred->user_ns);
    kmem_cache_free(cred_jar, cred);
}

void __put_cred(struct cred *cred)
{
    kdebug("__put_cred(%p{%d,%d})", cred,
           atomic_read(&cred->usage),
           read_cred_subscribers(cred));

    BUG_ON(atomic_read(&cred->usage) != 0);
#ifdef CONFIG_DEBUG_CREDENTIALS
    BUG_ON(read_cred_subscribers(cred) != 0);
    cred->magic = CRED_MAGIC_DEAD;
    cred->put_addr = __builtin_return_address(0);
#endif
    BUG_ON(cred == current->cred);
    BUG_ON(cred == current->real_cred);

    call_rcu(&cred->rcu, put_cred_rcu);
}
EXPORT_SYMBOL(__put_cred);

/*
 * Clean up a task's credentials when it exits
 */
void exit_creds(struct task_struct *tsk)
{
    struct cred *cred;

    kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,
           atomic_read(&tsk->cred->usage),
           read_cred_subscribers(tsk->cred));

    cred = (struct cred *) tsk->real_cred;
    tsk->real_cred = NULL;
    validate_creds(cred);
    alter_cred_subscribers(cred, -1);
    put_cred(cred);

    cred = (struct cred *) tsk->cred;
    tsk->cred = NULL;
    validate_creds(cred);
    alter_cred_subscribers(cred, -1);
    put_cred(cred);
}

const struct cred *get_task_cred(struct task_struct *task)
{
    const struct cred *cred;

    rcu_read_lock();

    do {
        cred = __task_cred((task));
        BUG_ON(!cred);
    } while (!atomic_inc_not_zero(&((struct cred *)cred)->usage));

    rcu_read_unlock();
    return cred;
}

/*
 * Allocate blank credentials, such that the credentials can be filled in at a
 * later date without risk of ENOMEM.
 */
struct cred *cred_alloc_blank(void)
{
    struct cred *new;

    new = kmem_cache_zalloc(cred_jar, GFP_KERNEL);
    if (!new)
        return NULL;

#ifdef CONFIG_KEYS
    new->tgcred = kzalloc(sizeof(*new->tgcred), GFP_KERNEL);
    if (!new->tgcred) {
        kmem_cache_free(cred_jar, new);
        return NULL;
    }
    atomic_set(&new->tgcred->usage, 1);
#endif

    atomic_set(&new->usage, 1);
#ifdef CONFIG_DEBUG_CREDENTIALS
    new->magic = CRED_MAGIC;
#endif

    if (security_cred_alloc_blank(new, GFP_KERNEL) < 0)
        goto error;

    return new;

error:
    abort_creds(new);
    return NULL;
}

struct cred *prepare_creds(void)
{
    struct task_struct *task = current;
    const struct cred *old;
    struct cred *new;

    validate_process_creds();

    new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
    if (!new)
        return NULL;

    kdebug("prepare_creds() alloc %p", new);

    old = task->cred;
    memcpy(new, old, sizeof(struct cred));

    atomic_set(&new->usage, 1);
    set_cred_subscribers(new, 0);
    get_group_info(new->group_info);
    get_uid(new->user);
    get_user_ns(new->user_ns);

#ifdef CONFIG_KEYS
    key_get(new->thread_keyring);
    key_get(new->request_key_auth);
    atomic_inc(&new->tgcred->usage);
#endif

#ifdef CONFIG_SECURITY
    new->security = NULL;
#endif

    if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
        goto error;
    validate_creds(new);
    return new;

error:
    abort_creds(new);
    return NULL;
}
EXPORT_SYMBOL(prepare_creds);

/*
 * Prepare credentials for current to perform an execve()
 * - The caller must hold ->cred_guard_mutex
 */
struct cred *prepare_exec_creds(void)
{
    struct thread_group_cred *tgcred = NULL;
    struct cred *new;

#ifdef CONFIG_KEYS
    tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
    if (!tgcred)
        return NULL;
#endif

    new = prepare_creds();
    if (!new) {
        kfree(tgcred);
        return new;
    }

#ifdef CONFIG_KEYS
    /* newly exec'd tasks don't get a thread keyring */
    key_put(new->thread_keyring);
    new->thread_keyring = NULL;

    /* create a new per-thread-group creds for all this set of threads to
     * share */
    memcpy(tgcred, new->tgcred, sizeof(struct thread_group_cred));

    atomic_set(&tgcred->usage, 1);
    spin_lock_init(&tgcred->lock);

    /* inherit the session keyring; new process keyring */
    key_get(tgcred->session_keyring);
    tgcred->process_keyring = NULL;

    release_tgcred(new);
    new->tgcred = tgcred;
#endif

    return new;
}

/*
 * Copy credentials for the new process created by fork()
 *
 * We share if we can, but under some circumstances we have to generate a new
 * set.
 *
 * The new process gets the current process's subjective credentials as its
 * objective and subjective credentials
 */
int copy_creds(struct task_struct *p, unsigned long clone_flags)
{
#ifdef CONFIG_KEYS
    struct thread_group_cred *tgcred;
#endif
    struct cred *new;
    int ret;

    if (
#ifdef CONFIG_KEYS
        !p->cred->thread_keyring &&
#endif
        clone_flags & CLONE_THREAD
        ) {
        p->real_cred = get_cred(p->cred);
        get_cred(p->cred);
        alter_cred_subscribers(p->cred, 2);
        kdebug("share_creds(%p{%d,%d})",
               p->cred, atomic_read(&p->cred->usage),
               read_cred_subscribers(p->cred));
        atomic_inc(&p->cred->user->processes);
        return 0;
    }

    new = prepare_creds();
    if (!new)
        return -ENOMEM;

    if (clone_flags & CLONE_NEWUSER) {
        ret = create_user_ns(new);
        if (ret < 0)
            goto error_put;
    }

#ifdef CONFIG_KEYS
    /* new threads get their own thread keyrings if their parent already
     * had one */
    if (new->thread_keyring) {
        key_put(new->thread_keyring);
        new->thread_keyring = NULL;
        if (clone_flags & CLONE_THREAD)
            install_thread_keyring_to_cred(new);
    }

    /* we share the process and session keyrings between all the threads in
     * a process - this is slightly icky as we violate COW credentials a
     * bit */
    if (!(clone_flags & CLONE_THREAD)) {
        tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
        if (!tgcred) {
            ret = -ENOMEM;
            goto error_put;
        }
        atomic_set(&tgcred->usage, 1);
        spin_lock_init(&tgcred->lock);
        tgcred->process_keyring = NULL;
        tgcred->session_keyring = key_get(new->tgcred->session_keyring);

        release_tgcred(new);
        new->tgcred = tgcred;
    }
#endif

    atomic_inc(&new->user->processes);
    p->cred = p->real_cred = get_cred(new);
    alter_cred_subscribers(new, 2);
    validate_creds(new);
    return 0;

error_put:
    put_cred(new);
    return ret;
}

int commit_creds(struct cred *new)
{
    struct task_struct *task = current;
    const struct cred *old = task->real_cred;

    kdebug("commit_creds(%p{%d,%d})", new,
           atomic_read(&new->usage),
           read_cred_subscribers(new));

    BUG_ON(task->cred != old);
#ifdef CONFIG_DEBUG_CREDENTIALS
    BUG_ON(read_cred_subscribers(old) < 2);
    validate_creds(old);
    validate_creds(new);
#endif
    BUG_ON(atomic_read(&new->usage) < 1);

    get_cred(new); /* we will require a ref for the subj creds too */

    /* dumpability changes */
    if (!uid_eq(old->euid, new->euid) ||
        !gid_eq(old->egid, new->egid) ||
        !uid_eq(old->fsuid, new->fsuid) ||
        !gid_eq(old->fsgid, new->fsgid) ||
        !cap_issubset(new->cap_permitted, old->cap_permitted)) {
        if (task->mm)
            set_dumpable(task->mm, suid_dumpable);
        task->pdeath_signal = 0;
        smp_wmb();
    }

    /* alter the thread keyring */
    if (!uid_eq(new->fsuid, old->fsuid))
        key_fsuid_changed(task);
    if (!gid_eq(new->fsgid, old->fsgid))
        key_fsgid_changed(task);

    /* do it
     * RLIMIT_NPROC limits on user->processes have already been checked
     * in set_user().
     */
    alter_cred_subscribers(new, 2);
    if (new->user != old->user)
        atomic_inc(&new->user->processes);
    rcu_assign_pointer(task->real_cred, new);
    rcu_assign_pointer(task->cred, new);
    if (new->user != old->user)
        atomic_dec(&old->user->processes);
    alter_cred_subscribers(old, -2);

    /* send notifications */
    if (!uid_eq(new->uid,   old->uid)  ||
        !uid_eq(new->euid,  old->euid) ||
        !uid_eq(new->suid,  old->suid) ||
        !uid_eq(new->fsuid, old->fsuid))
        proc_id_connector(task, PROC_EVENT_UID);

    if (!gid_eq(new->gid,   old->gid)  ||
        !gid_eq(new->egid,  old->egid) ||
        !gid_eq(new->sgid,  old->sgid) ||
        !gid_eq(new->fsgid, old->fsgid))
        proc_id_connector(task, PROC_EVENT_GID);

    /* release the old obj and subj refs both */
    put_cred(old);
    put_cred(old);
    return 0;
}
EXPORT_SYMBOL(commit_creds);

void abort_creds(struct cred *new)
{
    kdebug("abort_creds(%p{%d,%d})", new,
           atomic_read(&new->usage),
           read_cred_subscribers(new));

#ifdef CONFIG_DEBUG_CREDENTIALS
    BUG_ON(read_cred_subscribers(new) != 0);
#endif
    BUG_ON(atomic_read(&new->usage) < 1);
    put_cred(new);
}
EXPORT_SYMBOL(abort_creds);

const struct cred *override_creds(const struct cred *new)
{
    const struct cred *old = current->cred;

    kdebug("override_creds(%p{%d,%d})", new,
           atomic_read(&new->usage),
           read_cred_subscribers(new));

    validate_creds(old);
    validate_creds(new);
    get_cred(new);
    alter_cred_subscribers(new, 1);
    rcu_assign_pointer(current->cred, new);
    alter_cred_subscribers(old, -1);

    kdebug("override_creds() = %p{%d,%d}", old,
           atomic_read(&old->usage),
           read_cred_subscribers(old));
    return old;
}
EXPORT_SYMBOL(override_creds);

void revert_creds(const struct cred *old)
{
    const struct cred *override = current->cred;

    kdebug("revert_creds(%p{%d,%d})", old,
           atomic_read(&old->usage),
           read_cred_subscribers(old));

    validate_creds(old);
    validate_creds(override);
    alter_cred_subscribers(old, 1);
    rcu_assign_pointer(current->cred, old);
    alter_cred_subscribers(override, -1);
    put_cred(override);
}
EXPORT_SYMBOL(revert_creds);

/*
 * initialise the credentials stuff
 */
void __init cred_init(void)
{
    /* allocate a slab in which we can store credentials */
    cred_jar = kmem_cache_create("cred_jar", sizeof(struct cred),
                     0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
}

struct cred *prepare_kernel_cred(struct task_struct *daemon)
{
#ifdef CONFIG_KEYS
    struct thread_group_cred *tgcred;
#endif
    const struct cred *old;
    struct cred *new;

    new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
    if (!new)
        return NULL;

#ifdef CONFIG_KEYS
    tgcred = kmalloc(sizeof(*tgcred), GFP_KERNEL);
    if (!tgcred) {
        kmem_cache_free(cred_jar, new);
        return NULL;
    }
#endif

    kdebug("prepare_kernel_cred() alloc %p", new);

    if (daemon)
        old = get_task_cred(daemon);
    else
        old = get_cred(&init_cred);

    validate_creds(old);

    *new = *old;
    atomic_set(&new->usage, 1);
    set_cred_subscribers(new, 0);
    get_uid(new->user);
    get_user_ns(new->user_ns);
    get_group_info(new->group_info);

#ifdef CONFIG_KEYS
    atomic_set(&tgcred->usage, 1);
    spin_lock_init(&tgcred->lock);
    tgcred->process_keyring = NULL;
    tgcred->session_keyring = NULL;
    new->tgcred = tgcred;
    new->request_key_auth = NULL;
    new->thread_keyring = NULL;
    new->jit_keyring = KEY_REQKEY_DEFL_THREAD_KEYRING;
#endif

#ifdef CONFIG_SECURITY
    new->security = NULL;
#endif
    if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
        goto error;

    put_cred(old);
    validate_creds(new);
    return new;

error:
    put_cred(new);
    put_cred(old);
    return NULL;
}
EXPORT_SYMBOL(prepare_kernel_cred);

int set_security_override(struct cred *new, u32 secid)
{
    return security_kernel_act_as(new, secid);
}
EXPORT_SYMBOL(set_security_override);

int set_security_override_from_ctx(struct cred *new, const char *secctx)
{
    u32 secid;
    int ret;

    ret = security_secctx_to_secid(secctx, strlen(secctx), &secid);
    if (ret < 0)
        return ret;

    return set_security_override(new, secid);
}
EXPORT_SYMBOL(set_security_override_from_ctx);

int set_create_files_as(struct cred *new, struct inode *inode)
{
    new->fsuid = inode->i_uid;
    new->fsgid = inode->i_gid;
    return security_kernel_create_files_as(new, inode);
}
EXPORT_SYMBOL(set_create_files_as);

#ifdef CONFIG_DEBUG_CREDENTIALS

bool creds_are_invalid(const struct cred *cred)
{
    if (cred->magic != CRED_MAGIC)
        return true;
#ifdef CONFIG_SECURITY_SELINUX
    /*
     * cred->security == NULL if security_cred_alloc_blank() or
     * security_prepare_creds() returned an error.
     */
    if (selinux_is_enabled() && cred->security) {
        if ((unsigned long) cred->security < PAGE_SIZE)
            return true;
        if ((*(u32 *)cred->security & 0xffffff00) ==
            (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8))
            return true;
    }
#endif
    return false;
}
EXPORT_SYMBOL(creds_are_invalid);

/*
 * dump invalid credentials
 */
static void dump_invalid_creds(const struct cred *cred, const char *label,
                   const struct task_struct *tsk)
{
    printk(KERN_ERR "CRED: %s credentials: %p %s%s%s\n",
           label, cred,
           cred == &init_cred ? "[init]" : "",
           cred == tsk->real_cred ? "[real]" : "",
           cred == tsk->cred ? "[eff]" : "");
    printk(KERN_ERR "CRED: ->magic=%x, put_addr=%p\n",
           cred->magic, cred->put_addr);
    printk(KERN_ERR "CRED: ->usage=%d, subscr=%d\n",
           atomic_read(&cred->usage),
           read_cred_subscribers(cred));
    printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
        from_kuid_munged(&init_user_ns, cred->uid),
        from_kuid_munged(&init_user_ns, cred->euid),
        from_kuid_munged(&init_user_ns, cred->suid),
        from_kuid_munged(&init_user_ns, cred->fsuid));
    printk(KERN_ERR "CRED: ->*gid = { %d,%d,%d,%d }\n",
        from_kgid_munged(&init_user_ns, cred->gid),
        from_kgid_munged(&init_user_ns, cred->egid),
        from_kgid_munged(&init_user_ns, cred->sgid),
        from_kgid_munged(&init_user_ns, cred->fsgid));
#ifdef CONFIG_SECURITY
    printk(KERN_ERR "CRED: ->security is %p\n", cred->security);
    if ((unsigned long) cred->security >= PAGE_SIZE &&
        (((unsigned long) cred->security & 0xffffff00) !=
         (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8)))
        printk(KERN_ERR "CRED: ->security {%x, %x}\n",
               ((u32*)cred->security)[0],
               ((u32*)cred->security)[1]);
#endif
}

/*
 * report use of invalid credentials
 */
void __invalid_creds(const struct cred *cred, const char *file, unsigned line)
{
    printk(KERN_ERR "CRED: Invalid credentials\n");
    printk(KERN_ERR "CRED: At %s:%u\n", file, line);
    dump_invalid_creds(cred, "Specified", current);
    BUG();
}
EXPORT_SYMBOL(__invalid_creds);

/*
 * check the credentials on a process
 */
void __validate_process_creds(struct task_struct *tsk,
                  const char *file, unsigned line)
{
    if (tsk->cred == tsk->real_cred) {
        if (unlikely(read_cred_subscribers(tsk->cred) < 2 ||
                 creds_are_invalid(tsk->cred)))
            goto invalid_creds;
    } else {
        if (unlikely(read_cred_subscribers(tsk->real_cred) < 1 ||
                 read_cred_subscribers(tsk->cred) < 1 ||
                 creds_are_invalid(tsk->real_cred) ||
                 creds_are_invalid(tsk->cred)))
            goto invalid_creds;
    }
    return;

invalid_creds:
    printk(KERN_ERR "CRED: Invalid process credentials\n");
    printk(KERN_ERR "CRED: At %s:%u\n", file, line);

    dump_invalid_creds(tsk->real_cred, "Real", tsk);
    if (tsk->cred != tsk->real_cred)
        dump_invalid_creds(tsk->cred, "Effective", tsk);
    else
        printk(KERN_ERR "CRED: Effective creds == Real creds\n");
    BUG();
}
EXPORT_SYMBOL(__validate_process_creds);

/*
 * check creds for do_exit()
 */
void validate_creds_for_do_exit(struct task_struct *tsk)
{
    kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
           tsk->real_cred, tsk->cred,
           atomic_read(&tsk->cred->usage),
           read_cred_subscribers(tsk->cred));

    __validate_process_creds(tsk, __FILE__, __LINE__);
}

#endif /* CONFIG_DEBUG_CREDENTIALS */