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    Subject[PATCH AUTOSEL 5.4 202/330] proc: Use new infrastructure to fix deadlocks in execve
    Date
    From: Bernd Edlinger <bernd.edlinger@hotmail.de>

    [ Upstream commit 2db9dbf71bf98d02a0bf33e798e5bfd2a9944696 ]

    This changes lock_trace to use the new exec_update_mutex
    instead of cred_guard_mutex.

    This fixes possible deadlocks when the trace is accessing
    /proc/$pid/stack for instance.

    This should be safe, as the credentials are only used for reading,
    and task->mm is updated on execve under the new exec_update_mutex.

    Signed-off-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
    Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/proc/base.c | 6 +++---
    1 file changed, 3 insertions(+), 3 deletions(-)

    diff --git a/fs/proc/base.c b/fs/proc/base.c
    index ebea9501afb84..4fdfe4faa74ee 100644
    --- a/fs/proc/base.c
    +++ b/fs/proc/base.c
    @@ -403,11 +403,11 @@ print0:

    static int lock_trace(struct task_struct *task)
    {
    - int err = mutex_lock_killable(&task->signal->cred_guard_mutex);
    + int err = mutex_lock_killable(&task->signal->exec_update_mutex);
    if (err)
    return err;
    if (!ptrace_may_access(task, PTRACE_MODE_ATTACH_FSCREDS)) {
    - mutex_unlock(&task->signal->cred_guard_mutex);
    + mutex_unlock(&task->signal->exec_update_mutex);
    return -EPERM;
    }
    return 0;
    @@ -415,7 +415,7 @@ static int lock_trace(struct task_struct *task)

    static void unlock_trace(struct task_struct *task)
    {
    - mutex_unlock(&task->signal->cred_guard_mutex);
    + mutex_unlock(&task->signal->exec_update_mutex);
    }

    #ifdef CONFIG_STACKTRACE
    --
    2.25.1
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