On 7/17/20 7:48 AM, Dmitry Vyukov wrote: > On Sat, Jul 11, 2020 at 6:16 PM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: >> >> On Sat, Jul 11, 2020 at 5:52 PM Hristo Venev <hristo@xxxxxxxxxx> wrote: >>> >>> On Sat, 2020-07-11 at 17:31 +0200, Dmitry Vyukov wrote: >>>> Looking at the code more, I am not sure how it may not corrupt >>>> memory. >>>> There definitely should be some combinations where accessing >>>> sq_entries*sizeof(u32) more memory won't be OK. >>>> May be worth adding a test that allocates all possible sizes for >>>> sq/cq >>>> and fills both rings. >>> >>> The layout (after the fix) is roughly as follows: >>> >>> 1. struct io_rings - ~192 bytes, maybe 256 >>> 2. cqes - (32 << n) bytes >>> 3. sq_array - (4 << n) bytes >>> >>> The bug was that the sq_array was offset by (4 << n) bytes. I think >>> issues can only occur when >>> >>> PAGE_ALIGN(192 + (32 << n) + (4 << n) + (4 << n)) >>> != >>> PAGE_ALIGN(192 + (32 << n) + (4 << n)) >>> >>> It looks like this never happens. We got lucky. >> >> Interesting. CQ entries are larger and we have at least that many of >> them as SQ entries. I guess this + power-of-2-pages can make it never >> overflow. > > Hi Jens, > > I see this patch is in block/for-5.9/io_uring > Is this tree merged into linux-next? I don't see it in linux-next yet. > Or is it possible to get it into 5.8? Yes, that tree is in linux-next, and I'm surprised you don't see it there as it's been queued up for almost a week. Are you sure? I'm not going to apply it to both 5.9 and 5.8 trees. The bug has been there for a while, but doesn't really impact functionality. Hence I just queued it up for 5.9. If this had been a 5.8 commit that introduced it, I would have queued it up for 5.8. > The reason I am asking is that we have an intern (Necip in CC) working > on significantly extending io_uring coverage in syzkaller: > https://github.com/google/syzkaller/pull/1926 > Unfortunately we had to hardcode offset computation logic b/c the > intended way of using io_uring for normal programs represents an > additional obstacle for the fuzzer and the relations between syscalls > and writes to shared memory are even hard to express for the fuzzer. > We want to hardcode this new updated way of computing offsets, but > this means we probably won't get good coverage until the intern term > ends (+ may be good to discover some io_uring bugs before the > release). Sounds good > If it won't get into linux-next/mainline until 5.9, it's not a big > deal, but I wanted to ask. That's the plan, it'll go in as part of the 5.9 merge window. -- Jens Axboe
