netdev - Re: KASAN: use-after-free Write in detach_if

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Date:   Mon, 30 Oct 2017 10:40:37 -0700
From:   syzbot 
        <bot+c0733f3aab92fc116dc1d10d8a25f5bf1f739eff@...kaller.appspotmail.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     davem@...emloft.net, dvyukov@...gle.com, eric.dumazet@...il.com,
        jasowang@...hat.com, john.stultz@...aro.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        sboyd@...eaurora.org, syzkaller-bugs@...glegroups.com,
        tglx@...utronix.de
Subject: Re: KASAN: use-after-free Write in detach_if_pending

> On Mon, Oct 30, 2017 at 6:30 PM, Eric Dumazet <eric.dumazet@...il.com>  
> wrote:
>> On Mon, 2017-10-30 at 18:06 +0100, Dmitry Vyukov wrote:

>>> Yes, but hashes in random trees also don't tell much. A tree can be
>>> rebased so the hash will be lost. It can be a tree unknown to the
>>> system. Even if we find the commit by hash, in order to match it
>>> against other trees we will have to use the title anyway (or are there
>>> better options?), so using hashes becomes pointless.

>> We do not send hashes on random trees, but official SHA1 in David Miller
>> trees. They will be the same SHA1 in official Linus Torvalds tree.

>> Really, you make our life more difficult by pretending that hashes are
>> not the proper way.

>> They are reasons we use Fixes: tags all over the places, they are unique
>> in Linus tree.

>> Since syzbot gives a SHA1 itself, it must be using a tree, right ?

>> So a SHA1 that is guaranteed to enter the same tree is correct.

>> Please fix your bot.


> They don't necessary enter the same tree (that's more of an exception
> than the rule). For bugs that we find in Linus tree, fixes enter usb,
> kvm, block, sound, linux-next and a bunch of other trees that I never
> heard of. At the very least we will need a git repo address + commit
> hash. But then for say linux-next hashes disappear. And mm which is
> not a git tree at all (no hashes).
> And still the hashes will need to be explicitly marked as fixes (with
> #syz fix or something else). So that would look like:

unknown command "fix"

> ##syz fix: git://git.kernel.org/pub/scm/linux/kernel/git/mhocko/mm.git
> e7989f973ae1b90ec7c0b671c81f7f553affccbe
> which does not look much better than:
> ##syz fix: tun: do not arm flow_gc_timer in tun_flow_init()
> which also I think makes it easier for humans to ensure that they
> actually reference what they meant to reference (and maybe find the
> fix in other trees).