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    Subject[PATCH AUTOSEL 5.10 02/70] Add a reference to ucounts for each cred
    Date
    From: Alexey Gladkov <legion@kernel.org>

    [ Upstream commit 905ae01c4ae2ae3df05bb141801b1db4b7d83c61 ]

    For RLIMIT_NPROC and some other rlimits the user_struct that holds the
    global limit is kept alive for the lifetime of a process by keeping it
    in struct cred. Adding a pointer to ucounts in the struct cred will
    allow to track RLIMIT_NPROC not only for user in the system, but for
    user in the user_namespace.

    Updating ucounts may require memory allocation which may fail. So, we
    cannot change cred.ucounts in the commit_creds() because this function
    cannot fail and it should always return 0. For this reason, we modify
    cred.ucounts before calling the commit_creds().

    Changelog

    v6:
    * Fix null-ptr-deref in is_ucounts_overlimit() detected by trinity. This
    error was caused by the fact that cred_alloc_blank() left the ucounts
    pointer empty.

    Reported-by: kernel test robot <oliver.sang@intel.com>
    Signed-off-by: Alexey Gladkov <legion@kernel.org>
    Link: https://lkml.kernel.org/r/b37aaef28d8b9b0d757e07ba6dd27281bbe39259.1619094428.git.legion@kernel.org
    Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/exec.c | 4 ++++
    include/linux/cred.h | 2 ++
    include/linux/user_namespace.h | 4 ++++
    kernel/cred.c | 40 ++++++++++++++++++++++++++++++++++
    kernel/fork.c | 6 +++++
    kernel/sys.c | 12 ++++++++++
    kernel/ucount.c | 40 +++++++++++++++++++++++++++++++---
    kernel/user_namespace.c | 3 +++
    8 files changed, 108 insertions(+), 3 deletions(-)

    diff --git a/fs/exec.c b/fs/exec.c
    index ca89e0e3ef10..c7a4ef8df305 100644
    --- a/fs/exec.c
    +++ b/fs/exec.c
    @@ -1347,6 +1347,10 @@ int begin_new_exec(struct linux_binprm * bprm)
    WRITE_ONCE(me->self_exec_id, me->self_exec_id + 1);
    flush_signal_handlers(me, 0);

    + retval = set_cred_ucounts(bprm->cred);
    + if (retval < 0)
    + goto out_unlock;
    +
    /*
    * install the new credentials for this executable
    */
    diff --git a/include/linux/cred.h b/include/linux/cred.h
    index 18639c069263..ad160e5fe5c6 100644
    --- a/include/linux/cred.h
    +++ b/include/linux/cred.h
    @@ -144,6 +144,7 @@ struct cred {
    #endif
    struct user_struct *user; /* real user ID subscription */
    struct user_namespace *user_ns; /* user_ns the caps and keyrings are relative to. */
    + struct ucounts *ucounts;
    struct group_info *group_info; /* supplementary groups for euid/fsgid */
    /* RCU deletion */
    union {
    @@ -170,6 +171,7 @@ extern int set_security_override_from_ctx(struct cred *, const char *);
    extern int set_create_files_as(struct cred *, struct inode *);
    extern int cred_fscmp(const struct cred *, const struct cred *);
    extern void __init cred_init(void);
    +extern int set_cred_ucounts(struct cred *);

    /*
    * check for validity of credentials
    diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
    index 7616c7bf4b24..e1bd560da1cd 100644
    --- a/include/linux/user_namespace.h
    +++ b/include/linux/user_namespace.h
    @@ -101,11 +101,15 @@ struct ucounts {
    };

    extern struct user_namespace init_user_ns;
    +extern struct ucounts init_ucounts;

    bool setup_userns_sysctls(struct user_namespace *ns);
    void retire_userns_sysctls(struct user_namespace *ns);
    struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, enum ucount_type type);
    void dec_ucount(struct ucounts *ucounts, enum ucount_type type);
    +struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid);
    +struct ucounts *get_ucounts(struct ucounts *ucounts);
    +void put_ucounts(struct ucounts *ucounts);

    #ifdef CONFIG_USER_NS

    diff --git a/kernel/cred.c b/kernel/cred.c
    index 421b1149c651..58a8a9e24347 100644
    --- a/kernel/cred.c
    +++ b/kernel/cred.c
    @@ -60,6 +60,7 @@ struct cred init_cred = {
    .user = INIT_USER,
    .user_ns = &init_user_ns,
    .group_info = &init_groups,
    + .ucounts = &init_ucounts,
    };

    static inline void set_cred_subscribers(struct cred *cred, int n)
    @@ -119,6 +120,8 @@ static void put_cred_rcu(struct rcu_head *rcu)
    if (cred->group_info)
    put_group_info(cred->group_info);
    free_uid(cred->user);
    + if (cred->ucounts)
    + put_ucounts(cred->ucounts);
    put_user_ns(cred->user_ns);
    kmem_cache_free(cred_jar, cred);
    }
    @@ -222,6 +225,7 @@ struct cred *cred_alloc_blank(void)
    #ifdef CONFIG_DEBUG_CREDENTIALS
    new->magic = CRED_MAGIC;
    #endif
    + new->ucounts = get_ucounts(&init_ucounts);

    if (security_cred_alloc_blank(new, GFP_KERNEL_ACCOUNT) < 0)
    goto error;
    @@ -284,6 +288,11 @@ struct cred *prepare_creds(void)

    if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
    goto error;
    +
    + new->ucounts = get_ucounts(new->ucounts);
    + if (!new->ucounts)
    + goto error;
    +
    validate_creds(new);
    return new;

    @@ -363,6 +372,8 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
    ret = create_user_ns(new);
    if (ret < 0)
    goto error_put;
    + if (set_cred_ucounts(new) < 0)
    + goto error_put;
    }

    #ifdef CONFIG_KEYS
    @@ -653,6 +664,31 @@ int cred_fscmp(const struct cred *a, const struct cred *b)
    }
    EXPORT_SYMBOL(cred_fscmp);

    +int set_cred_ucounts(struct cred *new)
    +{
    + struct task_struct *task = current;
    + const struct cred *old = task->real_cred;
    + struct ucounts *old_ucounts = new->ucounts;
    +
    + if (new->user == old->user && new->user_ns == old->user_ns)
    + return 0;
    +
    + /*
    + * This optimization is needed because alloc_ucounts() uses locks
    + * for table lookups.
    + */
    + if (old_ucounts && old_ucounts->ns == new->user_ns && uid_eq(old_ucounts->uid, new->euid))
    + return 0;
    +
    + if (!(new->ucounts = alloc_ucounts(new->user_ns, new->euid)))
    + return -EAGAIN;
    +
    + if (old_ucounts)
    + put_ucounts(old_ucounts);
    +
    + return 0;
    +}
    +
    /*
    * initialise the credentials stuff
    */
    @@ -719,6 +755,10 @@ struct cred *prepare_kernel_cred(struct task_struct *daemon)
    if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
    goto error;

    + new->ucounts = get_ucounts(new->ucounts);
    + if (!new->ucounts)
    + goto error;
    +
    put_cred(old);
    validate_creds(new);
    return new;
    diff --git a/kernel/fork.c b/kernel/fork.c
    index 7c044d377926..281addb694df 100644
    --- a/kernel/fork.c
    +++ b/kernel/fork.c
    @@ -2960,6 +2960,12 @@ int ksys_unshare(unsigned long unshare_flags)
    if (err)
    goto bad_unshare_cleanup_cred;

    + if (new_cred) {
    + err = set_cred_ucounts(new_cred);
    + if (err)
    + goto bad_unshare_cleanup_cred;
    + }
    +
    if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
    if (do_sysvsem) {
    /*
    diff --git a/kernel/sys.c b/kernel/sys.c
    index a730c03ee607..0670e824e019 100644
    --- a/kernel/sys.c
    +++ b/kernel/sys.c
    @@ -552,6 +552,10 @@ long __sys_setreuid(uid_t ruid, uid_t euid)
    if (retval < 0)
    goto error;

    + retval = set_cred_ucounts(new);
    + if (retval < 0)
    + goto error;
    +
    return commit_creds(new);

    error:
    @@ -610,6 +614,10 @@ long __sys_setuid(uid_t uid)
    if (retval < 0)
    goto error;

    + retval = set_cred_ucounts(new);
    + if (retval < 0)
    + goto error;
    +
    return commit_creds(new);

    error:
    @@ -685,6 +693,10 @@ long __sys_setresuid(uid_t ruid, uid_t euid, uid_t suid)
    if (retval < 0)
    goto error;

    + retval = set_cred_ucounts(new);
    + if (retval < 0)
    + goto error;
    +
    return commit_creds(new);

    error:
    diff --git a/kernel/ucount.c b/kernel/ucount.c
    index 11b1596e2542..9894795043c4 100644
    --- a/kernel/ucount.c
    +++ b/kernel/ucount.c
    @@ -8,6 +8,12 @@
    #include <linux/kmemleak.h>
    #include <linux/user_namespace.h>

    +struct ucounts init_ucounts = {
    + .ns = &init_user_ns,
    + .uid = GLOBAL_ROOT_UID,
    + .count = 1,
    +};
    +
    #define UCOUNTS_HASHTABLE_BITS 10
    static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
    static DEFINE_SPINLOCK(ucounts_lock);
    @@ -125,7 +131,15 @@ static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struc
    return NULL;
    }

    -static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
    +static void hlist_add_ucounts(struct ucounts *ucounts)
    +{
    + struct hlist_head *hashent = ucounts_hashentry(ucounts->ns, ucounts->uid);
    + spin_lock_irq(&ucounts_lock);
    + hlist_add_head(&ucounts->node, hashent);
    + spin_unlock_irq(&ucounts_lock);
    +}
    +
    +struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
    {
    struct hlist_head *hashent = ucounts_hashentry(ns, uid);
    struct ucounts *ucounts, *new;
    @@ -160,7 +174,26 @@ static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
    return ucounts;
    }

    -static void put_ucounts(struct ucounts *ucounts)
    +struct ucounts *get_ucounts(struct ucounts *ucounts)
    +{
    + unsigned long flags;
    +
    + if (!ucounts)
    + return NULL;
    +
    + spin_lock_irqsave(&ucounts_lock, flags);
    + if (ucounts->count == INT_MAX) {
    + WARN_ONCE(1, "ucounts: counter has reached its maximum value");
    + ucounts = NULL;
    + } else {
    + ucounts->count += 1;
    + }
    + spin_unlock_irqrestore(&ucounts_lock, flags);
    +
    + return ucounts;
    +}
    +
    +void put_ucounts(struct ucounts *ucounts)
    {
    unsigned long flags;

    @@ -194,7 +227,7 @@ struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
    {
    struct ucounts *ucounts, *iter, *bad;
    struct user_namespace *tns;
    - ucounts = get_ucounts(ns, uid);
    + ucounts = alloc_ucounts(ns, uid);
    for (iter = ucounts; iter; iter = tns->ucounts) {
    int max;
    tns = iter->ns;
    @@ -237,6 +270,7 @@ static __init int user_namespace_sysctl_init(void)
    BUG_ON(!user_header);
    BUG_ON(!setup_userns_sysctls(&init_user_ns));
    #endif
    + hlist_add_ucounts(&init_ucounts);
    return 0;
    }
    subsys_initcall(user_namespace_sysctl_init);
    diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
    index ce396ea4de60..8206a13c81eb 100644
    --- a/kernel/user_namespace.c
    +++ b/kernel/user_namespace.c
    @@ -1340,6 +1340,9 @@ static int userns_install(struct nsset *nsset, struct ns_common *ns)
    put_user_ns(cred->user_ns);
    set_cred_user_ns(cred, get_user_ns(user_ns));

    + if (set_cred_ucounts(cred) < 0)
    + return -EINVAL;
    +
    return 0;
    }

    --
    2.30.2
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