On Fri, Jan 26, 2018 at 11:44:22AM +0800, Jason Wang wrote: > > > On 2018年01月26日 01:31, Michael S. Tsirkin wrote: > > On Thu, Jan 25, 2018 at 10:17:38PM +0800, Jason Wang wrote: > > > > > > On 2018年01月25日 21:45, Michael S. Tsirkin wrote: > > > > On Thu, Jan 25, 2018 at 03:31:42PM +0800, Jason Wang wrote: > > > > > We try to allocate one more entry for lockless peeking. The adding > > > > > operation may overflow which causes zero to be passed to kmalloc(). > > > > > In this case, it returns ZERO_SIZE_PTR without any notice by ptr > > > > > ring. Try to do producing or consuming on such ring will lead NULL > > > > > dereference. Fix this detect and fail early. > > > > > > > > > > Fixes: bcecb4bbf88a ("net: ptr_ring: otherwise safe empty checks can > > > > > overrun array bounds") > > > > > Reported-by:syzbot+87678bcf753b44c39...@syzkaller.appspotmail.com > > > > > Cc: John Fastabend<john.fastab...@gmail.com> > > > > > Signed-off-by: Jason Wang<jasow...@redhat.com> > > > > Ugh that's just way too ugly. > > > > I'll work on dropping the extra + 1 - but calling this > > > > function with -1 size is the real source of the bug. > > > > Do you know how come we do that? > > > > > > > It looks e.g try to change tx_queue_len to UINT_MAX. And we probably can't > > > prevent user form trying to do this? > > > > > > Thanks > > Right. BTW why net-next? Isn't the crash exploitable in net? > > > > Commit bcecb4bbf88a exists only in net-next.
Right you are. > And in net we check r->size > before trying to dereference the queue. > > Thanks I was wondering what it's about btw. Does anyone really create 0 size rings? -- MST