proc: hold cred_guard_mutex in check_mem_permission()
Avoid a potential race when task exec's and we get a new ->mm but check against the old credentials in ptrace_may_access(). Holding of the mutex is implemented by factoring out the body of the code into a helper function __check_mem_permission(). Performing this factorization now simplifies upcoming changes and minimizes churn in the diff's. Signed-off-by: Stephen Wilson <wilsons@start.ca> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
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@ -191,10 +191,7 @@ static int proc_root_link(struct inode *inode, struct path *path)
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return result;
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}
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/*
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* Return zero if current may access user memory in @task, -error if not.
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*/
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static int check_mem_permission(struct task_struct *task)
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static int __check_mem_permission(struct task_struct *task)
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{
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/*
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* A task can always look at itself, in case it chooses
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@ -222,6 +219,27 @@ static int check_mem_permission(struct task_struct *task)
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return -EPERM;
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}
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/*
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* Return zero if current may access user memory in @task, -error if not.
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*/
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static int check_mem_permission(struct task_struct *task)
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{
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int err;
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/*
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* Avoid racing if task exec's as we might get a new mm but validate
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* against old credentials.
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*/
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err = mutex_lock_killable(&task->signal->cred_guard_mutex);
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if (err)
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return err;
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err = __check_mem_permission(task);
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mutex_unlock(&task->signal->cred_guard_mutex);
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return err;
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}
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struct mm_struct *mm_for_maps(struct task_struct *task)
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{
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struct mm_struct *mm;
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