On Thu, Jun 14, 2018 at 10:03:09AM -0700, Cong Wang wrote: > On Thu, Jun 14, 2018 at 7:24 AM, Jason Gunthorpe <jgg@xxxxxxxxxxxx> wrote: > > > > This was my brief reaction too, this code path almost certainly has a > > use-after-free, and we should fix the concurrency between the two > > places in some correct way.. > > First of all, why use-after-free could trigger an imbalance unlock? > IOW, why do we have to solve use-after-free to fix this imbalance > unlock? The issue syzkaller hit is that accessing ctx->file does not seem locked in any way and can race with other manipulations of ctx->file. So.. for this patch to be correct we need to understand how this statement: f = ctx->file Avoids f becoming a dangling pointer - and without locking, my suspicion is that it doesn't - because missing locking around ctx->file is probably the actual bug syzkaller found. If this is not the case, then add a comment explaining how f's lifetime is OK. Otherwise, we need some kind of locking and guessing we need to hold a kref for f? > Third of all, the use-after-free I can see (race with ->close) exists > before my patch, this patch doesn't make it better or worse, nor > I have any intend to fix it. I'm not sure that race exists, there should be something that flushes the WQ on the path to close... (though I have another email that perhaps that is broken, sigh) Jason -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
