Messages in this thread | | | Date | Mon, 30 Jul 2018 12:23:49 +0200 | From | Dominique Martinet <> | Subject | Re: [PATCH] 9p: fix Use-After-Free in p9_write_work() |
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Tomas Bortoli wrote on Mon, Jul 30, 2018: > > Other transports also have the same issue see discussion in > > https://lkml.org/lkml/2018/7/19/727 > > (that is another syzbot report, slightly different but I believe it > > points to the same issue) > > > > Basically, a more global view of the problem is a race between > > p9_tag_lookup returning a p9_req_t and another thread freeing it. > > > > Matthew wrote the problem himself in a comment in p9_tag_lookup in his new > > version that used to be in linux-next at the time (I took the commit out > > temporarily until I've had time to benchmark it, but it will come back in, > > just you're working on thin air right now because the bug was only found > > thanks to this commit): > > + /* There's no refcount on the req; a malicious server could > > cause > > + * us to dereference a NULL pointer > > + */ > > > > So a more proper solution would be to had a refcount to req, have > > p9_tag_lookup increment the refcount within rcu_read_lock, and have a > > deref function free the req when the count hits 0. > > Which commit ? that's a comment.
Sorry, the commit is this one: http://lkml.kernel.org/r/20180711210225.19730-6-willy@infradead.org
It's now out of my 9p-next branch due to performance reasons but I'll definitely take it back in once my performance mitigation patches have had a few reviews.
> That sound like the proper solution. Let's do it that way then.
Cool :)
-- Dominique
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