On Sun, Dec 16, 2018 at 10:35 PM Peter Oskolkov <posk.de...@gmail.com> wrote:
>
> I guess DCCP is not used to the extent that 10 listeners per bucket
> happen in real life scenarios, so the issue is purely theoretical; as
> my patch would cause a sefgault for even a single listening dccp
> socket, I felt it was my patch that the "Fixes" tag should refer to.
>
Problem is : any host with a buggy kernel can trivially crash if a
malicious application
knows about this bug and exploit it.
This means we need to backport this fix to all kernels up to the real
root cause,
not only net-next on which your patch revealed this old bug.
Therefore we need a correct Fixes: tag so that proper stable
submissions can be done.
The Fixes: tag accuracy is paramount.
Thanks.
> On Sun, Dec 16, 2018 at 9:51 PM Eric Dumazet <eric.duma...@gmail.com> wrote:
> >
> >
> >
> > On 12/16/2018 03:42 PM, Peter Oskolkov wrote:
> > > Commit d9fbc7f6431f "net: tcp: prefer listeners bound to an address"
> > > removes port-only listener lookups. This caused segfaults in DCCP
> > > lookups because DCCP did not initialize the (addr,port) hashtable.
> > >
> > > This patch adds said initialization.
> > >
> > > The only non-trivial issue here is the size of the new hashtable.
> > > It seemed reasonable to make it match the size of the port-only
> > > hashtable (= INET_LHTABLE_SIZE) that was used previously. Other
> > > parameters to inet_hashinfo2_init() match those used in TCP.
> > >
> > > V2 changes: marked inet_hashinfo2_init as an exported symbol
> > > so that DCCP compiles when configured as a module.
> > >
> > > Tested: syzcaller issues fixed; the second patch in the patchset
> > > tests that DCCP lookups work correctly.
> > >
> > > Fixes: d9fbc7f6431f "net: tcp: prefer listeners bound to an address"
> >
> >
> > Strange, I would say bug was brought by commit 61b7c691c731
> > ("inet: Add a 2nd listener hashtable (port+addr)")
> >
> > The secondary hash table would have been used anyway if some application
> > (syzkaller-like)
> > had been using DCCP a bit more, to the point the second hash table would
> > have been used.
> >
> > With more than 10 listeners on one bucket, code in inet6_lookup_listener()
> > would
> > have attempted to deref a NULL pointer.
