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Re: Memory leaking in memmove

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ArifulHossain tuhin <etothepowerpi@gmail.com> writes:

> On Wednesday, December 28, 2011 4:36:37 PM UTC+6, Philip Lantz wrote:
>> ArifulHossain tuhin wrote:
>> > My application is leaking memory in a memmove call. I have made it
>> > sure from coredumps.
>> I don't think you mean "leaking memory". That term specifically refers 
>> to not freeing memory that was allocated. I'm guessing you mean that 
>> your program is overwriting memory that it shouldn't.
>> 
>> > the offending code snippet reads as follows:
>> > unsigned char pad_len;
>> > pad_len = (unsigned char)((random() % RANSTOP ) + RANSTART);
>> > if(pad_len%30 == 0)
>> > pad_len = 9;
>> > if(packet->size > 0){
>> > 	memmove(packet->data.buf + pad_len, packet->data.buf, packet->size);
>> > 	packet->size += pad_len;
>> > 	packet->data.buf[0] = pad_len;
>> > 	for(j=1; j< pad_len; j++)
>> > 	packet->data.buf[j] = (char)256%j;
>> > 	EnDeCrypt(packet->data.buf, packet->size, key, KEYLEN);
>> > }
>> > 
>> > As the data.buf is statically allocated, valgrind does not complain
>> > anything about it.
>> > Is it running out of memory? or any other problem?
>> > Any suggestion?
>> 
>> 
>> There is no dynamic memory allocation in the fragment you have shown us, 
>> so it can't be running out of memory.
>> 
>
> You are absolutely right. I guess i'm misinformed about terminologies. Thanks
>
>> Are you sure that packet->size + pad_len < sizeof packet->data.buf? That 
>> check should probably be in the code, unless there are constraints on 
>> the packet size that guarantee that it is always true.
>
> Packet size can be as high as 230 with pad_len. pad_len is unsigned char. so it should cover upto 256. sizeof(packet->data.buf) is 8 so it should not be a problem. Though i guess should put a checking into the code anyway.

How long is your actual packet buffer? - you say above that it's 8 but
you might be misunderstanding the question.  If not, then you'll have
problems.

If at any time packet_size + pad_len is longer than the size of
packet->data.buf then you'll be scribbling on memory you don't own.

Can you show us the code that defines and sets packet->data.buf

As packet->data.buf must contain at least as many bytes as the maximum
length of pad_len, can you tell us what RANSTOP and RANSTART are
#define'd to?

It might be worth printing pad_len just before the memmove and seeing
what the value is when it blows up.
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Memory leaking in memmove ArifulHossain tuhin <etothepowerpi@gmail.com> - 2011-12-28 01:24 -0800
  Re: Memory leaking in memmove Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-12-28 02:20 -0800
    Re: Memory leaking in memmove ArifulHossain tuhin <etothepowerpi@gmail.com> - 2011-12-28 02:37 -0800
      Re: Memory leaking in memmove Philip Lantz <prl@canterey.us> - 2011-12-28 02:42 -0800
      Re: Memory leaking in memmove Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-12-28 03:36 -0800
        Re: Memory leaking in memmove ArifulHossain tuhin <etothepowerpi@gmail.com> - 2011-12-28 03:50 -0800
      Re: Memory leaking in memmove Seebs <usenet-nospam@seebs.net> - 2011-12-28 18:17 +0000
  Re: Memory leaking in memmove Philip Lantz <prl@canterey.us> - 2011-12-28 02:36 -0800
    Re: Memory leaking in memmove ArifulHossain tuhin <etothepowerpi@gmail.com> - 2011-12-28 03:57 -0800
      Re: Memory leaking in memmove Dr Nick <3-nospam@temporary-address.org.uk> - 2011-12-28 12:21 +0000
        Re: Memory leaking in memmove ArifulHossain tuhin <etothepowerpi@gmail.com> - 2011-12-28 04:26 -0800
      Re: Memory leaking in memmove jt@toerring.de (Jens Thoms Toerring) - 2011-12-28 12:46 +0000
  Re: Memory leaking in memmove ArifulHossain tuhin <etothepowerpi@gmail.com> - 2011-12-28 05:54 -0800
  Re: Memory leaking in memmove Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-12-28 14:46 +0000
    Re: Memory leaking in memmove Philip Lantz <prl@canterey.us> - 2011-12-28 12:20 -0800
      Re: Memory leaking in memmove Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-12-28 21:50 +0000
  Re: Memory leaking in memmove Barry Schwarz <schwarzb@dqel.com> - 2011-12-28 10:36 -0800

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