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    Subject[resend][PATCH 3/4] move cred_guard_mutex from task_struct to signal_struct
    Date
    Changelog
    o since v1
    - function comment also change current->cred_guard_mutex to
    current->signal->cred_guard_mutex.

    ---------------------------------------------------------------------------
    Oleg Nesterov pointed out we have to prevent multiple-threads-inside-exec
    itself and we can reuse ->cred_guard_mutex for it. Yes, concurrent
    execve() has no worth.

    Let's move ->cred_guard_mutex from task_struct to signal_struct. It
    naturally prevent multiple-threads-inside-exec.

    Cc: stable@kernel.org
    Reviewed-by: Oleg Nesterov <oleg@redhat.com>
    Cc: Roland McGrath <roland@redhat.com>
    Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    ---
    fs/exec.c | 10 +++++-----
    fs/proc/base.c | 8 ++++----
    include/linux/init_task.h | 4 ++--
    include/linux/sched.h | 7 ++++---
    include/linux/tracehook.h | 2 +-
    kernel/cred.c | 4 +---
    kernel/fork.c | 2 ++
    kernel/ptrace.c | 4 ++--
    8 files changed, 21 insertions(+), 20 deletions(-)

    diff --git a/fs/exec.c b/fs/exec.c
    index 6d2b6f9..94dabd2 100644
    --- a/fs/exec.c
    +++ b/fs/exec.c
    @@ -1078,14 +1078,14 @@ EXPORT_SYMBOL(setup_new_exec);
    */
    int prepare_bprm_creds(struct linux_binprm *bprm)
    {
    - if (mutex_lock_interruptible(&current->cred_guard_mutex))
    + if (mutex_lock_interruptible(&current->signal->cred_guard_mutex))
    return -ERESTARTNOINTR;

    bprm->cred = prepare_exec_creds();
    if (likely(bprm->cred))
    return 0;

    - mutex_unlock(&current->cred_guard_mutex);
    + mutex_unlock(&current->signal->cred_guard_mutex);
    return -ENOMEM;
    }

    @@ -1093,7 +1093,7 @@ void free_bprm(struct linux_binprm *bprm)
    {
    free_arg_pages(bprm);
    if (bprm->cred) {
    - mutex_unlock(&current->cred_guard_mutex);
    + mutex_unlock(&current->signal->cred_guard_mutex);
    abort_creds(bprm->cred);
    }
    kfree(bprm);
    @@ -1114,13 +1114,13 @@ void install_exec_creds(struct linux_binprm *bprm)
    * credentials; any time after this it may be unlocked.
    */
    security_bprm_committed_creds(bprm);
    - mutex_unlock(&current->cred_guard_mutex);
    + mutex_unlock(&current->signal->cred_guard_mutex);
    }
    EXPORT_SYMBOL(install_exec_creds);

    /*
    * determine how safe it is to execute the proposed program
    - * - the caller must hold current->cred_guard_mutex to protect against
    + * - the caller must hold ->cred_guard_mutex to protect against
    * PTRACE_ATTACH
    */
    int check_unsafe_exec(struct linux_binprm *bprm)
    diff --git a/fs/proc/base.c b/fs/proc/base.c
    index 0d2ce21..d3ea8b0 100644
    --- a/fs/proc/base.c
    +++ b/fs/proc/base.c
    @@ -226,7 +226,7 @@ struct mm_struct *mm_for_maps(struct task_struct *task)
    {
    struct mm_struct *mm;

    - if (mutex_lock_killable(&task->cred_guard_mutex))
    + if (mutex_lock_killable(&task->signal->cred_guard_mutex))
    return NULL;

    mm = get_task_mm(task);
    @@ -235,7 +235,7 @@ struct mm_struct *mm_for_maps(struct task_struct *task)
    mmput(mm);
    mm = NULL;
    }
    - mutex_unlock(&task->cred_guard_mutex);
    + mutex_unlock(&task->signal->cred_guard_mutex);

    return mm;
    }
    @@ -2277,14 +2277,14 @@ static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
    goto out_free;

    /* Guard against adverse ptrace interaction */
    - length = mutex_lock_interruptible(&task->cred_guard_mutex);
    + length = mutex_lock_interruptible(&task->signal->cred_guard_mutex);
    if (length < 0)
    goto out_free;

    length = security_setprocattr(task,
    (char*)file->f_path.dentry->d_name.name,
    (void*)page, count);
    - mutex_unlock(&task->cred_guard_mutex);
    + mutex_unlock(&task->signal->cred_guard_mutex);
    out_free:
    free_page((unsigned long) page);
    out:
    diff --git a/include/linux/init_task.h b/include/linux/init_task.h
    index 2fea6c8..1f8c06c 100644
    --- a/include/linux/init_task.h
    +++ b/include/linux/init_task.h
    @@ -29,6 +29,8 @@ extern struct fs_struct init_fs;
    .running = 0, \
    .lock = __SPIN_LOCK_UNLOCKED(sig.cputimer.lock), \
    }, \
    + .cred_guard_mutex = \
    + __MUTEX_INITIALIZER(sig.cred_guard_mutex), \
    }

    extern struct nsproxy init_nsproxy;
    @@ -145,8 +147,6 @@ extern struct cred init_cred;
    .group_leader = &tsk, \
    RCU_INIT_POINTER(.real_cred, &init_cred), \
    RCU_INIT_POINTER(.cred, &init_cred), \
    - .cred_guard_mutex = \
    - __MUTEX_INITIALIZER(tsk.cred_guard_mutex), \
    .comm = "swapper", \
    .thread = INIT_THREAD, \
    .fs = &init_fs, \
    diff --git a/include/linux/sched.h b/include/linux/sched.h
    index 74ed859..ac65605 100644
    --- a/include/linux/sched.h
    +++ b/include/linux/sched.h
    @@ -626,6 +626,10 @@ struct signal_struct {

    int oom_adj; /* OOM kill score adjustment (bit shift) */
    long oom_score_adj; /* OOM kill score adjustment */
    +
    + struct mutex cred_guard_mutex; /* guard against foreign influences on
    + * credential calculations
    + * (notably. ptrace) */
    };

    /* Context switch must be unlocked if interrupts are to be enabled */
    @@ -1305,9 +1309,6 @@ struct task_struct {
    * credentials (COW) */
    const struct cred __rcu *cred; /* effective (overridable) subjective task
    * credentials (COW) */
    - struct mutex cred_guard_mutex; /* guard against foreign influences on
    - * credential calculations
    - * (notably. ptrace) */
    struct cred *replacement_session_keyring; /* for KEYCTL_SESSION_TO_PARENT */

    char comm[TASK_COMM_LEN]; /* executable name excluding path
    diff --git a/include/linux/tracehook.h b/include/linux/tracehook.h
    index 10db010..3a2e66d 100644
    --- a/include/linux/tracehook.h
    +++ b/include/linux/tracehook.h
    @@ -150,7 +150,7 @@ static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
    *
    * Return %LSM_UNSAFE_* bits applied to an exec because of tracing.
    *
    - * @task->cred_guard_mutex is held by the caller through the do_execve().
    + * @task->signal->cred_guard_mutex is held by the caller through the do_execve().
    */
    static inline int tracehook_unsafe_exec(struct task_struct *task)
    {
    diff --git a/kernel/cred.c b/kernel/cred.c
    index 9a3e226..6a1aa00 100644
    --- a/kernel/cred.c
    +++ b/kernel/cred.c
    @@ -325,7 +325,7 @@ EXPORT_SYMBOL(prepare_creds);

    /*
    * Prepare credentials for current to perform an execve()
    - * - The caller must hold current->cred_guard_mutex
    + * - The caller must hold ->cred_guard_mutex
    */
    struct cred *prepare_exec_creds(void)
    {
    @@ -384,8 +384,6 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
    struct cred *new;
    int ret;

    - mutex_init(&p->cred_guard_mutex);
    -
    if (
    #ifdef CONFIG_KEYS
    !p->cred->thread_keyring &&
    diff --git a/kernel/fork.c b/kernel/fork.c
    index c445f8c..8c09cf9 100644
    --- a/kernel/fork.c
    +++ b/kernel/fork.c
    @@ -904,6 +904,8 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
    sig->oom_adj = current->signal->oom_adj;
    sig->oom_score_adj = current->signal->oom_score_adj;

    + mutex_init(&sig->cred_guard_mutex);
    +
    return 0;
    }

    diff --git a/kernel/ptrace.c b/kernel/ptrace.c
    index f34d798..ac5013a 100644
    --- a/kernel/ptrace.c
    +++ b/kernel/ptrace.c
    @@ -181,7 +181,7 @@ int ptrace_attach(struct task_struct *task)
    * under ptrace.
    */
    retval = -ERESTARTNOINTR;
    - if (mutex_lock_interruptible(&task->cred_guard_mutex))
    + if (mutex_lock_interruptible(&task->signal->cred_guard_mutex))
    goto out;

    task_lock(task);
    @@ -208,7 +208,7 @@ int ptrace_attach(struct task_struct *task)
    unlock_tasklist:
    write_unlock_irq(&tasklist_lock);
    unlock_creds:
    - mutex_unlock(&task->cred_guard_mutex);
    + mutex_unlock(&task->signal->cred_guard_mutex);
    out:
    return retval;
    }
    --
    1.6.5.2




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