On Fri, Dec 22, 2017 at 01:31:26PM +0800, Xin Long wrote:
> On Thu, Dec 21, 2017 at 9:13 PM, Marcelo Ricardo Leitner
> <marcelo.leitner@xxxxxxxxx> wrote:
> > On Wed, Dec 20, 2017 at 12:51:01PM -0800, syzbot wrote:
> >
> > from the log:
> > [ 89.451366] FAULT_INJECTION: forcing a failure.^M
> > [ 89.451366] name failslab, interval 1, probability 0, space 0,
> > times 0^M
> > [ 89.451374] CPU: 0 PID: 17287 Comm: syz-executor2 Not tainted
> > +4.15.0-rc3-next-20171214+ #67^M
> > [ 89.451377] Hardware name: Google Google Compute Engine/Google
> > Compute Engine, BIOS
> > +Google 01/01/2011^M
> > [ 89.451380] Call Trace:^M
> > [ 89.451395] dump_stack+0xe9/0x14b^M
> > [ 89.451408] should_fail+0x1e5/0x220^M
> > [ 89.451419] should_failslab+0x73/0x90^M
> > [ 89.451428] __kmalloc+0x63/0x730^M
> > [ 89.451439] ? rcu_read_lock_sched_held+0x74/0x80^M
> > [ 89.451446] ? __kmalloc+0x4ac/0x730^M
> > [ 89.451452] ? sctp_stream_alloc_in+0x2f/0x100^M
> > [ 89.451464] sctp_stream_alloc_in+0x2f/0x100^M
> > [ 89.451473] sctp_stream_init+0xfa/0x140^M
> > [ 89.451485] sctp_process_init+0x676/0xc50^M
> >
> > this is what caused the panic later, because in the error path we free
> > out but don't zero outcnt. This patch should fix it. Can you please
> > try it? Thanks
> >
> > ----8<---
> >
> > diff --git a/net/sctp/stream.c b/net/sctp/stream.c
> > index 06b644dd858c..50ab09029f00 100644
> > --- a/net/sctp/stream.c
> > +++ b/net/sctp/stream.c
> > @@ -184,6 +184,7 @@ int sctp_stream_init(struct sctp_stream *stream, __u16 outcnt, __u16 incnt,
> > sched->free(stream);
> > kfree(stream->out);
> > stream->out = NULL;
> > + stream->outcnt = 0;
> > out:
> > return ret;
> > }
>
> In case it can't be verified due to no reproducer yet, I modified some
> code in sctp_stream_init() to confirm Marcelo's deduction:
> - i = sctp_stream_alloc_in(stream, incnt, gfp);
> + i = 1;
> if (i) {
> ret = -ENOMEM;
> goto free;
>
> And got the same call trace as the mail:
>
> [ 301.488065] BUG: unable to handle kernel NULL pointer dereference
> at 0000000000000008
> [ 301.488618] IP: sctp_stream_free+0x2c/0x60 [sctp]
> [ 301.488928] PGD 59a3b067 P4D 59a3b067 PUD 5994e067 PMD 0
> [ 301.489372] Oops: 0000 [#1] SMP
> [...]
> [ 301.497647] Call Trace:
> [ 301.497812] <IRQ>
> [ 301.497955] sctp_association_free+0xb8/0x210 [sctp]
> [ 301.498306] sctp_sf_do_5_1B_init+0x1c4/0x360 [sctp]
> [ 301.498654] sctp_do_sm+0x9a/0x2d0 [sctp]
> [ 301.498921] ? sctp_has_association+0x130/0x130 [sctp]
> [ 301.499301] ? kernel_text_address+0xba/0xe0
> [ 301.499615] ? check_usage_backwards+0x88/0x150
> [ 301.499911] ? __lock_acquire+0x280/0x1080
> [ 301.500200] ? sctp_endpoint_lookup_assoc+0x95/0x140 [sctp]
> [ 301.500593] sctp_endpoint_bh_rcv+0x11e/0x220 [sctp]
> [ 301.500923] sctp_rcv+0x9f5/0xbe0 [sctp]
>
> And Marcelo's patch could fix it.
>
> Since the "free:" part only works for if (i), maybe the patch can also do:
> if (i) {
> sched->free(stream);
> kfree(stream->out);
> stream->out = NULL;
> stream->outcnt = 0;
>
> ret = -ENOMEM;
> goto out;
> }
>
> and remove the "free:" path.
This crash seems to have stopped occurring now. I presume it was fixed by the
following commit, so let's tell syzbot to close the bug:
#syz fix: sctp: fix error path in sctp_stream_init
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