Messages in this thread Patch in this message |  | | Date | Tue, 23 Jun 2009 21:25:32 +0200 | From | Oleg Nesterov <> | Subject | [PATCH 1/1] mm_for_maps: simplify, use ptrace_may_access() |
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It would be nice to kill __ptrace_may_access(). It requires task_lock(), but this lock is only needed to read mm->flags in the middle.
Convert mm_for_maps() to use ptrace_may_access(), this also simplifies the code a little bit.
Also, we do not need to take ->mmap_sem in advance. In fact I think mm_for_maps() should not play with ->mmap_sem at all, the caller should take this lock.
With or without this patch, without ->cred_guard_mutex held we can race with exec() and get the new ->mm but check old creds.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
--- WAIT/fs/proc/base.c~1_MM_FOR_MAPS 2009-06-17 14:11:26.000000000 +0200 +++ WAIT/fs/proc/base.c 2009-06-23 20:16:44.000000000 +0200 @@ -237,20 +237,19 @@ struct mm_struct *mm_for_maps(struct tas struct mm_struct *mm = get_task_mm(task); if (!mm) return NULL; + if (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); + return NULL; + } + } down_read(&mm->mmap_sem); - task_lock(task); - if (task->mm != mm) - goto out; - if (task->mm != current->mm && - __ptrace_may_access(task, PTRACE_MODE_READ) < 0) - goto out; - task_unlock(task); return mm; -out: - task_unlock(task); - up_read(&mm->mmap_sem); - mmput(mm); - return NULL; } static int proc_pid_cmdline(struct task_struct *task, char * buffer)
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