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sched/core: Fix use-after-free bug in dup_user_cpus_ptr()
commit87ca4f9efb
upstream. Since commit07ec77a1d4
("sched: Allow task CPU affinity to be restricted on asymmetric systems"), the setting and clearing of user_cpus_ptr are done under pi_lock for arm64 architecture. However, dup_user_cpus_ptr() accesses user_cpus_ptr without any lock protection. Since sched_setaffinity() can be invoked from another process, the process being modified may be undergoing fork() at the same time. When racing with the clearing of user_cpus_ptr in __set_cpus_allowed_ptr_locked(), it can lead to user-after-free and possibly double-free in arm64 kernel. Commit8f9ea86fdf
("sched: Always preserve the user requested cpumask") fixes this problem as user_cpus_ptr, once set, will never be cleared in a task's lifetime. However, this bug was re-introduced in commit851a723e45
("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()") which allows the clearing of user_cpus_ptr in do_set_cpus_allowed(). This time, it will affect all arches. Fix this bug by always clearing the user_cpus_ptr of the newly cloned/forked task before the copying process starts and check the user_cpus_ptr state of the source task under pi_lock. Note to stable, this patch won't be applicable to stable releases. Just copy the new dup_user_cpus_ptr() function over. Fixes:07ec77a1d4
("sched: Allow task CPU affinity to be restricted on asymmetric systems") Fixes:851a723e45
("sched: Always clear user_cpus_ptr in do_set_cpus_allowed()") Reported-by: David Wang 王标 <wangbiao3@xiaomi.com> Signed-off-by: Waiman Long <longman@redhat.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Reviewed-by: Peter Zijlstra <peterz@infradead.org> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20221231041120.440785-2-longman@redhat.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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parent
3c6e4995c0
commit
5c28e3bb22
1 changed files with 33 additions and 4 deletions
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@ -2501,14 +2501,43 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
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int dup_user_cpus_ptr(struct task_struct *dst, struct task_struct *src,
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int node)
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{
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if (!src->user_cpus_ptr)
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cpumask_t *user_mask;
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unsigned long flags;
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/*
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* Always clear dst->user_cpus_ptr first as their user_cpus_ptr's
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* may differ by now due to racing.
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*/
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dst->user_cpus_ptr = NULL;
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/*
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* This check is racy and losing the race is a valid situation.
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* It is not worth the extra overhead of taking the pi_lock on
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* every fork/clone.
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*/
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if (data_race(!src->user_cpus_ptr))
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return 0;
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dst->user_cpus_ptr = kmalloc_node(cpumask_size(), GFP_KERNEL, node);
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if (!dst->user_cpus_ptr)
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user_mask = kmalloc_node(cpumask_size(), GFP_KERNEL, node);
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if (!user_mask)
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return -ENOMEM;
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cpumask_copy(dst->user_cpus_ptr, src->user_cpus_ptr);
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/*
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* Use pi_lock to protect content of user_cpus_ptr
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*
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* Though unlikely, user_cpus_ptr can be reset to NULL by a concurrent
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* do_set_cpus_allowed().
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*/
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raw_spin_lock_irqsave(&src->pi_lock, flags);
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if (src->user_cpus_ptr) {
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swap(dst->user_cpus_ptr, user_mask);
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cpumask_copy(dst->user_cpus_ptr, src->user_cpus_ptr);
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}
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raw_spin_unlock_irqrestore(&src->pi_lock, flags);
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if (unlikely(user_mask))
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kfree(user_mask);
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return 0;
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}
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