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We
were also experiencing the "ping of death" with lwIP 1.3.0, and traced the
problem to the static buffer used for IP fragmenting.
If you
are using fragmenting, and set IP_FRAG_USES_STATIC_BUF in your lwipopts.h file,
a static buffer of size IP_FRAG_MAX_MTU is created. The problem is that
the code to create the static buffer in ip_frag.c is:
static
u8_t buf[LWIP_MEM_ALIGN_SIZE(IP_FRAG_MAX_MTU)]; // line 602 of
ip_frag.c
This
code rounds your IP_FRAG_MAX_MTU up to the next MEM_ALIGNMENT boundary. We
used an MTU of 1500, with a 128-byte memory alignment, so the buffer became 1536
bytes. The problem is that this buffer is then aligned in memory to a
MEM_ALIGNMENT boundary using the code:
rambuf->payload = LWIP_MEM_ALIGN((void *)buf); // line 653 of
ip_frag.c
For
us, this could move the start of the buffer forward by as many as 124
bytes. This meant that our 1536-byte buffer sometimes had less than 1500
bytes actually available. When this shortened buffer was
used, lwIP wrote into the next thing in memory (the ARP table for us),
and made the application crash.
You
can fix this in lwipopts.h by increasing IP_FRAG_MAX_MTU by MEM_ALIGNMENT
bytes.
I
think really the code should be fixed so line 602 reads:
static u8_t
buf[LWIP_MEM_ALIGN_SIZE(IP_FRAG_MAX_MTU+MEM_ALIGNMENT)];
This is similar
to what is done for ram_heap in mem.c, and probably other places in
lwIP.
Not sure if this
will help for everyone, but it fixed the problem for
us.
John
Keil
Hi list,
I have succesfully ported lwip 1.3.0 to
LPC2468. Lwip is running in a threaded environment, FreeRTOS. I have a basic
example running, with a webserver.
I have enabled ip reassembly, see my
lwipopts.h file attached to this mail.
I have a webbrowser running, which is
requesting a webpage from the webserver each second, and I am pinging the
system continually, through the command
Ping <ip> -t
The system is running ok. But if I ping
the system with a lot of data bytes, i.e. ping <ip> -l 2048. The system
crashes.
I end up in an data abort exception. The
reason for this exception, is a pointer, r, in function ip_reass() is
containing an invalid address.
The line in C code
is:
iprh = (struct
ip_reass_helper*)r->payload;
// line number: 572 in ip_frag.c
What can I do, to avoid this ping of
death ?
P.S.: Please be aware that I have yet to
optimize the system regarding values in lwipopts.h. But that will be a topic
for another question on this list.
Regards,
Martin
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