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proc: hold cred_guard_mutex in check_mem_permission()

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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>
This commit is contained in:
Stephen Wilson 2011-03-13 15:49:22 -04:00 committed by Al Viro
parent 26947f8c8f
commit 18f661bcf8
1 changed files with 22 additions and 4 deletions
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26
fs/proc/base.c
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@ -191,10 +191,7 @@ static int proc_root_link(struct inode *inode, struct path *path)
return result;
}
/*
* Return zero if current may access user memory in @task, -error if not.
*/
static int check_mem_permission(struct task_struct *task)
static int __check_mem_permission(struct task_struct *task)
{
/*
* A task can always look at itself, in case it chooses
@ -222,6 +219,27 @@ static int check_mem_permission(struct task_struct *task)
return -EPERM;
}
/*
* Return zero if current may access user memory in @task, -error if not.
*/
static int check_mem_permission(struct task_struct *task)
{
int err;
/*
* Avoid racing if task exec's as we might get a new mm but validate
* against old credentials.
*/
err = mutex_lock_killable(&task->signal->cred_guard_mutex);
if (err)
return err;
err = __check_mem_permission(task);
mutex_unlock(&task->signal->cred_guard_mutex);
return err;
}
struct mm_struct *mm_for_maps(struct task_struct *task)
{
struct mm_struct *mm;