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    SubjectRe: [syzbot] KASAN: use-after-free Read in srcu_invoke_callbacks
    On Fri, Jan 14, 2022 at 07:27:52AM -0800, Paul E. McKenney wrote:
    > On Fri, Jan 14, 2022 at 10:38:42PM +0800, Boqun Feng wrote:
    > > Hi,
    > >
    > > On Tue, Jan 11, 2022 at 11:05:00AM -0800, Paul E. McKenney wrote:
    > > [...]
    > > > > > The buggy address belongs to the object at ffff8880189b5c70
    > > > > > which belongs to the cache request_queue_srcu of size 3816
    > >
    > > This cache name drew my attention when I was trying to look into this,
    > > because I couldn't find it in v5.16, later on I realized the UAF was
    > > found in linux-next and the commit introducing the cache was merged into
    > > mainline if 5.17 merge window:
    > >
    > > 704b914f15fb blk-mq: move srcu from blk_mq_hw_ctx to request_queue
    > >
    > > I think the UAF is actually a bug introduced by the commit, because in
    > > that commit srcu structure was moved from blk_mq_hw_ctx to
    > > request_queue, and therefore the cleanup_srcu_struct() should be moved
    > > from blk_mq_hw_sysfs_release() to blk_release_queue(), however the above
    > > commit only deleted the one in blk_mq_hw_sysfs_release() but didn't add
    > > a new one in blk_release_queue(). As a result when a request queue is
    > > freed, the srcu structure is not fully clean up, therefore the UAF.
    > >
    > > IOW, something like below (untested) should fix this. Copy the auther
    > > and block maintainers.
    >
    > One question for the author and block maintainers... Why not simply have
    > a single srcu_struct for all of the queues? Or is there some situation
    > where you need one queue's reader to avoid blocking other queues' SRCU
    > grace periods?

    Because srcu_struct is too fat, and only few drivers need it, and
    most block drivers needn't it.


    Thanks,
    Ming

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