Messages in this thread | | | Date | Fri, 14 Jan 2022 08:11:38 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [syzbot] KASAN: use-after-free Read in srcu_invoke_callbacks |
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On Fri, Jan 14, 2022 at 11:58:24PM +0800, Ming Lei wrote: > 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.
Fair points.
But would it make sense to dynamically allocate a single srcu_struct when the first need arose, and only remove it when the last need passed?
Thanx, Paul
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