From 79d0895140e937ba111e6420b4cd83ee75efa788 Mon Sep 17 00:00:00 2001 From: Marcelo Ricardo Leitner Date: Tue, 2 Jan 2018 19:44:37 -0200 Subject: sctp: fix error path in sctp_stream_init syzbot noticed a NULL pointer dereference panic in sctp_stream_free() which was caused by an incomplete error handling in sctp_stream_init(). By not clearing stream->outcnt, it made a for() in sctp_stream_free() think that it had elements to free, but not, leading to the panic. As suggested by Xin Long, this patch also simplifies the error path by moving it to the only if() that uses it. See-also: https://www.spinics.net/lists/netdev/msg473756.html See-also: https://www.spinics.net/lists/netdev/msg465024.html Reported-by: syzbot Fixes: f952be79cebd ("sctp: introduce struct sctp_stream_out_ext") Signed-off-by: Marcelo Ricardo Leitner Reviewed-by: Xin Long Acked-by: Neil Horman Signed-off-by: David S. Miller --- net/sctp/stream.c | 22 ++++++++++------------ 1 file changed, 10 insertions(+), 12 deletions(-) (limited to 'net/sctp') diff --git a/net/sctp/stream.c b/net/sctp/stream.c index 76ea66be0bbe..524dfeb94c41 100644 --- a/net/sctp/stream.c +++ b/net/sctp/stream.c @@ -156,9 +156,9 @@ int sctp_stream_init(struct sctp_stream *stream, __u16 outcnt, __u16 incnt, sctp_stream_outq_migrate(stream, NULL, outcnt); sched->sched_all(stream); - i = sctp_stream_alloc_out(stream, outcnt, gfp); - if (i) - return i; + ret = sctp_stream_alloc_out(stream, outcnt, gfp); + if (ret) + goto out; stream->outcnt = outcnt; for (i = 0; i < stream->outcnt; i++) @@ -170,19 +170,17 @@ in: if (!incnt) goto out; - i = sctp_stream_alloc_in(stream, incnt, gfp); - if (i) { - ret = -ENOMEM; - goto free; + ret = sctp_stream_alloc_in(stream, incnt, gfp); + if (ret) { + sched->free(stream); + kfree(stream->out); + stream->out = NULL; + stream->outcnt = 0; + goto out; } stream->incnt = incnt; - goto out; -free: - sched->free(stream); - kfree(stream->out); - stream->out = NULL; out: return ret; } -- cgit v1.2.3 From cc35c3d1edf7a8373a1a5daa80a912dec96a9cd5 Mon Sep 17 00:00:00 2001 From: Marcelo Ricardo Leitner Date: Fri, 5 Jan 2018 11:17:17 -0200 Subject: sctp: do not retransmit upon FragNeeded if PMTU discovery is disabled Currently, if PMTU discovery is disabled on a given transport, but the configured value is higher than the actual PMTU, it is likely that we will get some icmp Frag Needed. The issue is, if PMTU discovery is disabled, we won't update the information and will issue a retransmission immediately, which may very well trigger another ICMP, and another retransmission, leading to a loop. The fix is to simply not trigger immediate retransmissions if PMTU discovery is disabled on the given transport. Changes from v2: - updated stale comment, noticed by Xin Long Signed-off-by: Marcelo Ricardo Leitner Signed-off-by: David S. Miller --- net/sctp/input.c | 24 ++++++++++++------------ 1 file changed, 12 insertions(+), 12 deletions(-) (limited to 'net/sctp') diff --git a/net/sctp/input.c b/net/sctp/input.c index 621b5ca3fd1c..9320661cc41d 100644 --- a/net/sctp/input.c +++ b/net/sctp/input.c @@ -399,20 +399,20 @@ void sctp_icmp_frag_needed(struct sock *sk, struct sctp_association *asoc, return; } - if (t->param_flags & SPP_PMTUD_ENABLE) { - /* Update transports view of the MTU */ - sctp_transport_update_pmtu(t, pmtu); + if (!(t->param_flags & SPP_PMTUD_ENABLE)) + /* We can't allow retransmitting in such case, as the + * retransmission would be sized just as before, and thus we + * would get another icmp, and retransmit again. + */ + return; - /* Update association pmtu. */ - sctp_assoc_sync_pmtu(asoc); - } + /* Update transports view of the MTU */ + sctp_transport_update_pmtu(t, pmtu); - /* Retransmit with the new pmtu setting. - * Normally, if PMTU discovery is disabled, an ICMP Fragmentation - * Needed will never be sent, but if a message was sent before - * PMTU discovery was disabled that was larger than the PMTU, it - * would not be fragmented, so it must be re-transmitted fragmented. - */ + /* Update association pmtu. */ + sctp_assoc_sync_pmtu(asoc); + + /* Retransmit with the new pmtu setting. */ sctp_retransmit(&asoc->outqueue, t, SCTP_RTXR_PMTUD); } -- cgit v1.2.3 From b6c5734db07079c9410147b32407f2366d584e6c Mon Sep 17 00:00:00 2001 From: Marcelo Ricardo Leitner Date: Fri, 5 Jan 2018 11:17:18 -0200 Subject: sctp: fix the handling of ICMP Frag Needed for too small MTUs syzbot reported a hang involving SCTP, on which it kept flooding dmesg with the message: [ 246.742374] sctp: sctp_transport_update_pmtu: Reported pmtu 508 too low, using default minimum of 512 That happened because whenever SCTP hits an ICMP Frag Needed, it tries to adjust to the new MTU and triggers an immediate retransmission. But it didn't consider the fact that MTUs smaller than the SCTP minimum MTU allowed (512) would not cause the PMTU to change, and issued the retransmission anyway (thus leading to another ICMP Frag Needed, and so on). As IPv4 (ip_rt_min_pmtu=556) and IPv6 (IPV6_MIN_MTU=1280) minimum MTU are higher than that, sctp_transport_update_pmtu() is changed to re-fetch the PMTU that got set after our request, and with that, detect if there was an actual change or not. The fix, thus, skips the immediate retransmission if the received ICMP resulted in no change, in the hope that SCTP will select another path. Note: The value being used for the minimum MTU (512, SCTP_DEFAULT_MINSEGMENT) is not right and instead it should be (576, SCTP_MIN_PMTU), but such change belongs to another patch. Changes from v1: - do not disable PMTU discovery, in the light of commit 06ad391919b2 ("[SCTP] Don't disable PMTU discovery when mtu is small") and as suggested by Xin Long. - changed the way to break the rtx loop by detecting if the icmp resulted in a change or not Changes from v2: none See-also: https://lkml.org/lkml/2017/12/22/811 Reported-by: syzbot Signed-off-by: Marcelo Ricardo Leitner Signed-off-by: David S. Miller --- net/sctp/input.c | 8 ++++++-- net/sctp/transport.c | 29 +++++++++++++++++++---------- 2 files changed, 25 insertions(+), 12 deletions(-) (limited to 'net/sctp') diff --git a/net/sctp/input.c b/net/sctp/input.c index 9320661cc41d..141c9c466ec1 100644 --- a/net/sctp/input.c +++ b/net/sctp/input.c @@ -406,8 +406,12 @@ void sctp_icmp_frag_needed(struct sock *sk, struct sctp_association *asoc, */ return; - /* Update transports view of the MTU */ - sctp_transport_update_pmtu(t, pmtu); + /* Update transports view of the MTU. Return if no update was needed. + * If an update wasn't needed/possible, it also doesn't make sense to + * try to retransmit now. + */ + if (!sctp_transport_update_pmtu(t, pmtu)) + return; /* Update association pmtu. */ sctp_assoc_sync_pmtu(asoc); diff --git a/net/sctp/transport.c b/net/sctp/transport.c index 1e5a22430cf5..47f82bd794d9 100644 --- a/net/sctp/transport.c +++ b/net/sctp/transport.c @@ -248,28 +248,37 @@ void sctp_transport_pmtu(struct sctp_transport *transport, struct sock *sk) transport->pathmtu = SCTP_DEFAULT_MAXSEGMENT; } -void sctp_transport_update_pmtu(struct sctp_transport *t, u32 pmtu) +bool sctp_transport_update_pmtu(struct sctp_transport *t, u32 pmtu) { struct dst_entry *dst = sctp_transport_dst_check(t); + bool change = true; if (unlikely(pmtu < SCTP_DEFAULT_MINSEGMENT)) { - pr_warn("%s: Reported pmtu %d too low, using default minimum of %d\n", - __func__, pmtu, SCTP_DEFAULT_MINSEGMENT); - /* Use default minimum segment size and disable - * pmtu discovery on this transport. - */ - t->pathmtu = SCTP_DEFAULT_MINSEGMENT; - } else { - t->pathmtu = pmtu; + pr_warn_ratelimited("%s: Reported pmtu %d too low, using default minimum of %d\n", + __func__, pmtu, SCTP_DEFAULT_MINSEGMENT); + /* Use default minimum segment instead */ + pmtu = SCTP_DEFAULT_MINSEGMENT; } + pmtu = SCTP_TRUNC4(pmtu); if (dst) { dst->ops->update_pmtu(dst, t->asoc->base.sk, NULL, pmtu); dst = sctp_transport_dst_check(t); } - if (!dst) + if (!dst) { t->af_specific->get_dst(t, &t->saddr, &t->fl, t->asoc->base.sk); + dst = t->dst; + } + + if (dst) { + /* Re-fetch, as under layers may have a higher minimum size */ + pmtu = SCTP_TRUNC4(dst_mtu(dst)); + change = t->pathmtu != pmtu; + } + t->pathmtu = pmtu; + + return change; } /* Caches the dst entry and source address for a transport's destination -- cgit v1.2.3