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authorOleg Nesterov <oleg@redhat.com>2009-07-10 03:27:40 +0200
committerJames Morris <jmorris@namei.org>2009-08-10 20:49:26 +1000
commit704b836cbf19e885f8366bccb2e4b0474346c02d (patch)
treed0513d3ef70e1b875cd7786f94150ba2428b6a88
parent00f89d218523b9bf6b522349c039d5ac80aa536d (diff)
downloadconfigs-704b836cbf19e885f8366bccb2e4b0474346c02d.tar.gz
mm_for_maps: take ->cred_guard_mutex to fix the race with exec
The problem is minor, but without ->cred_guard_mutex held we can race with exec() and get the new ->mm but check old creds. Now we do not need to re-check task->mm after ptrace_may_access(), it can't be changed to the new mm under us. Strictly speaking, this also fixes another very minor problem. Unless security check fails or the task exits mm_for_maps() should never return NULL, the caller should get either old or new ->mm. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Serge Hallyn <serue@us.ibm.com> Signed-off-by: James Morris <jmorris@namei.org>
-rw-r--r--fs/proc/base.c22
1 files changed, 11 insertions, 11 deletions
diff --git a/fs/proc/base.c b/fs/proc/base.c
index f3c2e4085fe..175db258942 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -234,19 +234,19 @@ static int check_mem_permission(struct task_struct *task)
struct mm_struct *mm_for_maps(struct task_struct *task)
{
- struct mm_struct *mm = get_task_mm(task);
+ struct mm_struct *mm;
- if (mm && mm != current->mm) {
- /*
- * task->mm can be changed before security check,
- * in that case we must notice the change after.
- */
- if (!ptrace_may_access(task, PTRACE_MODE_READ) ||
- mm != task->mm) {
- mmput(mm);
- mm = NULL;
- }
+ if (mutex_lock_killable(&task->cred_guard_mutex))
+ return NULL;
+
+ mm = get_task_mm(task);
+ if (mm && mm != current->mm &&
+ !ptrace_may_access(task, PTRACE_MODE_READ)) {
+ mmput(mm);
+ mm = NULL;
}
+ mutex_unlock(&task->cred_guard_mutex);
+
return mm;
}