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Re: Memory leaking in memmove

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On Wednesday, December 28, 2011 6:21:03 PM UTC+6, Dr Nick wrote:
> ArifulHossain tuhin <etothe...@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.
> 
Its given in the original post.Below the code snippet, the structure definition of packet is given there. Its about 8192 bytes long. more than enough to hold multiple copies. I was talking about the data type of packet->data.buf which unsigned char.

> 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?
> 

3 and 9

> 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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