rijndael.cpp alloca issue using make on mingw

[zootaloo]

I saw this was brought up in another thread but I just wanted to make
sure I got this right. I am using plane-jane mingw/msys on winxp
(don't shoot me) and the only error I get while running make is:

g++ -DNDEBUG -g -O2 -pipe -c rijndael.cpp
rijndael.cpp: In member function `virtual size_t
CryptoPP::Rijndael::Enc::AdvancedProcessBlocks(const byte*, const
byte*, byte*, size_t, CryptoPP::word32) const':
rijndael.cpp:945: error: `alloca' was not declared in this scope
make: *** [rijndael.o] Error 1

I did some searching and supposedly stdlib.h has alloca, but that is
the not the case for my compiler and tool set (using g++ 3.4.5 and
msys 1.0). So I just changed line 945 from:

space = (byte *)alloca(255+sizeof(Locals));

to

space = (byte *)malloc(255+sizeof(Locals));

It compiled fine. I have not tested the function. What is the
difference between alloca and malloc? I see none and read that alloca
is ancient and should be put to rest.

Let me know if this is a no-no.
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[zooko]

Here is a patch that fixes that issue for me:

http://allmydata.org/trac/pycryptopp/changeset?new=622% 
40cryptopp&old=620%40cryptopp

This patch was initially committed to the pycryptopp repository in  
two steps:

http://allmydata.org/trac/pycryptopp/changeset/621/cryptopp
http://allmydata.org/trac/pycryptopp/changeset/622/cryptopp

Regards,

Zooko

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[Rafael Vargas-3]

Regarding the alloca and malloc difference.

You can't just change the code from alloca to malloc because malloc allocates memory from the heap and has to be free'd while alloca allocates memory from the stack and the memory is "free'd" when the function returns.

If you change the code from alloca to malloc you have to explicitly free the pointer returned by malloc.

--
Vargas

P.S.: Sorry by the duplicate mail Zooko, I've replied to you instead of replying to the group.

On Tue, Sep 15, 2009 at 13:19, Zooko Wilcox-O'Hearn <zooko@...> wrote:

Here is a patch that fixes that issue for me:

http://allmydata.org/trac/pycryptopp/changeset?new=622%
40cryptopp&old=620%40cryptopp

This patch was initially committed to the pycryptopp repository in
two steps:

http://allmydata.org/trac/pycryptopp/changeset/621/cryptopp
http://allmydata.org/trac/pycryptopp/changeset/622/cryptopp

Regards,

Zooko

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[zootaloo]

I read about that fix and tried it before, but sadly it does not fix my install. I do not have alloca in any library, stdlib included. So the fix for an apple compiler does not work for the winxp mingw compiler tool set.

Again, I am wondering what is wrong with using malloc vs alloca. Why is this the only spot in the whole crypto library that alloca is being used? Can it be changed to malloc given the same function ins/outs and then there would be no need for sun/apple specific exceptions.

Thanks for your time,
K

On Tue, Sep 15, 2009 at 12:19 PM, Zooko Wilcox-O'Hearn <zooko@...> wrote:

Here is a patch that fixes that issue for me:

http://allmydata.org/trac/pycryptopp/changeset?new=622%40cryptopp&old=620%40cryptopp

This patch was initially committed to the pycryptopp repository in two steps:

http://allmydata.org/trac/pycryptopp/changeset/621/cryptopp
http://allmydata.org/trac/pycryptopp/changeset/622/cryptopp

Regards,

Zooko

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[Rafael Vargas-3]

I guess you can change from "alloca" to "malloc", but you have to remember to free the memory before the return statement.
--
Vargas

On Thu, Sep 17, 2009 at 18:21, Kevin Nasman <zootaloo99@...> wrote:

I read about that fix and tried it before, but sadly it does not fix my install. I do not have alloca in any library, stdlib included. So the fix for an apple compiler does not work for the winxp mingw compiler tool set.

Again, I am wondering what is wrong with using malloc vs alloca. Why is this the only spot in the whole crypto library that alloca is being used? Can it be changed to malloc given the same function ins/outs and then there would be no need for sun/apple specific exceptions.

Thanks for your time,
K

On Tue, Sep 15, 2009 at 12:19 PM, Zooko Wilcox-O'Hearn <zooko@...> wrote:

Here is a patch that fixes that issue for me:

http://allmydata.org/trac/pycryptopp/changeset?new=622%40cryptopp&old=620%40cryptopp

This patch was initially committed to the pycryptopp repository in two steps:

http://allmydata.org/trac/pycryptopp/changeset/621/cryptopp
http://allmydata.org/trac/pycryptopp/changeset/622/cryptopp

Regards,

Zooko

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[Wei Dai]

No, please don't do that. Alloca is being used to find some stack space that isn't cache-aliased with static lookup tables, in order to defend against timing attacks. It's easy to just apply Zooko's fix. I'll also get this fixed in the next release.

From: rsvargas@...

Sent: Thursday, September 17, 2009 2:45 PM

To: zootaloo99@...

Cc: cryptopp-users@...

Subject: Re: rijndael.cpp alloca issue using make on mingw

I guess you can change from "alloca" to "malloc", but you have to remember to free the memory before the return statement.
--
Vargas

On Thu, Sep 17, 2009 at 18:21, Kevin Nasman <zootaloo99@...> wrote:

I read about that fix and tried it before, but sadly it does not fix my install. I do not have alloca in any library, stdlib included. So the fix for an apple compiler does not work for the winxp mingw compiler tool set.

Again, I am wondering what is wrong with using malloc vs alloca. Why is this the only spot in the whole crypto library that alloca is being used? Can it be changed to malloc given the same function ins/outs and then there would be no need for sun/apple specific exceptions.

Thanks for your time,
K

On Tue, Sep 15, 2009 at 12:19 PM, Zooko Wilcox-O'Hearn <zooko@...> wrote:

Here is a patch that fixes that issue for me:

http://allmydata.org/trac/pycryptopp/changeset?new=622%40cryptopp&old=620%40cryptopp

This patch was initially committed to the pycryptopp repository in two steps:

http://allmydata.org/trac/pycryptopp/changeset/621/cryptopp
http://allmydata.org/trac/pycryptopp/changeset/622/cryptopp

Regards,

Zooko

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[Wei Dai]

Kevin, the relevant fix for mingw is "#include <malloc.h>", not "#include <stdlib.h>".

From: zootaloo99@...

Sent: Thursday, September 17, 2009 2:21 PM

To: zooko@...

Cc: cryptopp-users@...

Subject: Re: rijndael.cpp alloca issue using make on mingw

I read about that fix and tried it before, but sadly it does not fix my install. I do not have alloca in any library, stdlib included. So the fix for an apple compiler does not work for the winxp mingw compiler tool set.

Again, I am wondering what is wrong with using malloc vs alloca. Why is this the only spot in the whole crypto library that alloca is being used? Can it be changed to malloc given the same function ins/outs and then there would be no need for sun/apple specific exceptions.

Thanks for your time,
K

On Tue, Sep 15, 2009 at 12:19 PM, Zooko Wilcox-O'Hearn <zooko@...> wrote:

Here is a patch that fixes that issue for me:

http://allmydata.org/trac/pycryptopp/changeset?new=622%40cryptopp&old=620%40cryptopp

This patch was initially committed to the pycryptopp repository in two steps:

http://allmydata.org/trac/pycryptopp/changeset/621/cryptopp
http://allmydata.org/trac/pycryptopp/changeset/622/cryptopp

Regards,

Zooko

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[zootaloo]

OK thank you very much that makes more sense to me now (with regards to difference between alloca and malloc).

-k

On Thu, Sep 17, 2009 at 8:55 PM, Wei Dai <weidai@...> wrote:

Kevin, the relevant fix for mingw is "#include <malloc.h>", not "#include <stdlib.h>".

From: zootaloo99@...

Sent: Thursday, September 17, 2009 2:21 PM

To: zooko@...

Cc: cryptopp-users@...

Subject: Re: rijndael.cpp alloca issue using make on mingw

I read about that fix and tried it before, but sadly it does not fix my install. I do not have alloca in any library, stdlib included. So the fix for an apple compiler does not work for the winxp mingw compiler tool set.

Again, I am wondering what is wrong with using malloc vs alloca. Why is this the only spot in the whole crypto library that alloca is being used? Can it be changed to malloc given the same function ins/outs and then there would be no need for sun/apple specific exceptions.

Thanks for your time,
K

On Tue, Sep 15, 2009 at 12:19 PM, Zooko Wilcox-O'Hearn <zooko@...> wrote:

Here is a patch that fixes that issue for me:

http://allmydata.org/trac/pycryptopp/changeset?new=622%40cryptopp&old=620%40cryptopp

This patch was initially committed to the pycryptopp repository in two steps:

http://allmydata.org/trac/pycryptopp/changeset/621/cryptopp
http://allmydata.org/trac/pycryptopp/changeset/622/cryptopp

Regards,

Zooko

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