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[lwip-devel] [bug #58817] SNTP - MEMP_SYS_TIMEOUT memory pool exhaustion
From: |
Jon Welch |
Subject: |
[lwip-devel] [bug #58817] SNTP - MEMP_SYS_TIMEOUT memory pool exhaustion when receive KOD packet |
Date: |
Fri, 24 Jul 2020 07:23:58 -0400 (EDT) |
User-agent: |
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/84.0.4147.89 Safari/537.36 Edg/84.0.522.40 |
URL:
<https://savannah.nongnu.org/bugs/?58817>
Summary: SNTP - MEMP_SYS_TIMEOUT memory pool exhaustion when
receive KOD packet
Project: lwIP - A Lightweight TCP/IP stack
Submitted by: g7jjf
Submitted on: Fri 24 Jul 2020 11:23:56 AM UTC
Category: apps
Severity: 3 - Normal
Item Group: Faulty Behaviour
Status: None
Privacy: Public
Assigned to: None
Open/Closed: Open
Discussion Lock: Any
Planned Release: None
lwIP version: git head
_______________________________________________________
Details:
There appears to be an issue when receiving SNTP Kiss Of Death packets. After
receiving several KOD packets, I started to see 'sys_timeout: timeout != NULL,
pool MEMP_SYS_TIMEOUT is empty' assertions displayed.
Looking at SNTP.C, around line 536, we have two sys_untimeout functions calls
to cancel active timeouts when receiving a good packet. However, there isn't a
corresponding sys_untimeout(sntp_request) just before the sntp_try_next_server
call around line 553 when receiving a KOD packet. Since the timeout isn't
cancelled, this appears to reduce the memory pool which eventually results in
the assertion displayed above. Changing the code to :
if (sntp_opmode == SNTP_OPMODE_POLL) {
/* Kiss-of-death packet. Use another server or increase UPDATE_DELAY.
*/
sys_untimeout(sntp_request, NULL);
sntp_try_next_server(NULL);
}
appears to solve the problem.
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