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[lwip-devel] [bug #58817] SNTP - MEMP_SYS_TIMEOUT memory pool exhaustion

From: yuanjianmin
Subject: [lwip-devel] [bug #58817] SNTP - MEMP_SYS_TIMEOUT memory pool exhaustion when receive KOD packet
Date: Thu, 20 May 2021 06:02:19 -0400 (EDT)
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:88.0) Gecko/20100101 Firefox/88.0

Follow-up Comment #1, bug #58817 (project lwip):

[comment #0 original submission:]
> 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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