[PATCH AUTOSEL 5.6 226/606] sctp: Don't add the shutdown timer if its already been added

Sasha Levin
2020-06-09T00:26:15Z

From: Neil Horman <nhorman@tuxdriver.com>

[ Upstream commit 20a785aa52c82246055a089e55df9dac47d67da1 ]

This BUG halt was reported a while back, but the patch somehow got
missed:

PID: 2879 TASK: c16adaa0 CPU: 1 COMMAND: "sctpn"
#0 [f418dd28] crash_kexec at c04a7d8c
#1 [f418dd7c] oops_end at c0863e02
#2 [f418dd90] do_invalid_op at c040aaca
#3 [f418de28] error_code (via invalid_op) at c08631a5
EAX: f34baac0 EBX: 00000090 ECX: f418deb0 EDX: f5542950 EBP: 00000000
DS: 007b ESI: f34ba800 ES: 007b EDI: f418dea0 GS: 00e0
CS: 0060 EIP: c046fa5e ERR: ffffffff EFLAGS: 00010286
#4 [f418de5c] add_timer at c046fa5e
#5 [f418de68] sctp_do_sm at f8db8c77 [sctp]
#6 [f418df30] sctp_primitive_SHUTDOWN at f8dcc1b5 [sctp]
#7 [f418df48] inet_shutdown at c080baf9
#8 [f418df5c] sys_shutdown at c079eedf
#9 [f418df70] sys_socketcall at c079fe88
EAX: ffffffda EBX: 0000000d ECX: bfceea90 EDX: 0937af98
DS: 007b ESI: 0000000c ES: 007b EDI: b7150ae4
SS: 007b ESP: bfceea7c EBP: bfceeaa8 GS: 0033
CS: 0073 EIP: b775c424 ERR: 00000066 EFLAGS: 00000282

It appears that the side effect that starts the shutdown timer was processed
multiple times, which can happen as multiple paths can trigger it. This of
course leads to the BUG halt in add_timer getting called.

Fix seems pretty straightforward, just check before the timer is added if its
already been started. If it has mod the timer instead to min(current
expiration, new expiration)

Its been tested but not confirmed to fix the problem, as the issue has only
occured in production environments where test kernels are enjoined from being
installed. It appears to be a sane fix to me though. Also, recentely,
Jere found a reproducer posted on list to confirm that this resolves the
issues

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: Vlad Yasevich <vyasevich@gmail.com>
CC: "David S. Miller" <davem@davemloft.net>
CC: jere.leppanen@nokia.com
CC: marcelo.leitner@gmail.com
CC: netdev@vger.kernel.org
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sctp/sm_sideeffect.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
index 2bc29463e1dc..9f36fe911d08 100644
--- a/net/sctp/sm_sideeffect.c
+++ b/net/sctp/sm_sideeffect.c
@@ -1523,9 +1523,17 @@ static int sctp_cmd_interpreter(enum sctp_event_type event_type,
timeout = asoc->timeouts[cmd->obj.to];
BUG_ON(!timeout);

- timer->expires = jiffies + timeout;
- sctp_association_hold(asoc);
- add_timer(timer);
+ /*
+ * SCTP has a hard time with timer starts. Because we process
+ * timer starts as side effects, it can be hard to tell if we
+ * have already started a timer or not, which leads to BUG
+ * halts when we call add_timer. So here, instead of just starting
+ * a timer, if the timer is already started, and just mod
+ * the timer with the shorter of the two expiration times
+ */
+ if (!timer_pending(timer))
+ sctp_association_hold(asoc);
+ timer_reduce(timer, jiffies + timeout);
break;

case SCTP_CMD_TIMER_RESTART:
--
2.25.1