[zeromq-dev] How to use zmq_getsockopt with option ZMQ_IDENTITY_FD
Suppose the identity string is only two bytes long, I pad with zeros to get a string of eight bytes. What should the value of option_len be, 2 or 8? -- Peter Kleiweg http://pkleiweg.home.xs4all.nl/ ___ zeromq-dev mailing list zeromq-dev@lists.zeromq.org http://lists.zeromq.org/mailman/listinfo/zeromq-dev
Re: [zeromq-dev] How to use zmq_getsockopt with option ZMQ_IDENTITY_FD
This is an oddball API choice (and there is a bug in the implementation), in that option_value* is being used as both and input and an output parameter. The size you pass in must be be *at least* sizeof(fd_t) bytes, because it will overwrite the supplied identity string with the resulting file descriptor. The bug is, it does not check to see that the size of supplied output is sufficient to hold sizeof(fd_t), so bad things (stack/heap corruption) would happen if you actually passed option_len = 2. On Thu, Jan 8, 2015 at 7:26 AM, Peter Kleiweg pklei...@xs4all.nl wrote: Suppose the identity string is only two bytes long, I pad with zeros to get a string of eight bytes. What should the value of option_len be, 2 or 8? -- Peter Kleiweg http://pkleiweg.home.xs4all.nl/ ___ zeromq-dev mailing list zeromq-dev@lists.zeromq.org http://lists.zeromq.org/mailman/listinfo/zeromq-dev ___ zeromq-dev mailing list zeromq-dev@lists.zeromq.org http://lists.zeromq.org/mailman/listinfo/zeromq-dev
Re: [zeromq-dev] How to use zmq_getsockopt with option ZMQ_IDENTITY_FD
yes.
using blob_t = std::basic_stringunsigned char;
char buf[8] = { 'f', 'o', 'o', 0, 0, 0, 0, 0 };
blob_t a(foo);
blob_t b(buf, 8);
assert(a == b); // fails
I think there is another issue with all of this. By default (IIRC) the
identity is 5 bytes, so on a 64 bit platform, the passed in identity would
never be sufficient to receive sizeof(fd_t) if fd_t was in fact defined as
a UINT_PTR. I don't have a Windows machine handy so I can't verify what
sizeof(SOCKET) returns, but as many of Window's 'handle' types are in fact
pointers, I suspect this might also be an issue when fd_t is typedef'd to
SOCKET. On Posix systems, it's fine.
On Thu, Jan 8, 2015 at 8:28 AM, Peter Kleiweg pklei...@xs4all.nl wrote:
Thomas Rodgers schreef op de 8e dag van de louwmaand van het jaar 2015:
This is an oddball API choice (and there is a bug in the implementation),
in that option_value* is being used as both and input and an output
parameter.
The size you pass in must be be *at least* sizeof(fd_t) bytes, because it
will overwrite the supplied identity string with the resulting file
descriptor. The bug is, it does not check to see that the size of
supplied
output is sufficient to hold sizeof(fd_t), so bad things (stack/heap
corruption) would happen if you actually passed option_len = 2.
But option_len is used for retrieving the identity string:
blob_t identity= blob_t((unsigned char*)optval_,*optvallen_);
Won't I get a wrong 'blob' if I use option_len = 8?
On Thu, Jan 8, 2015 at 7:26 AM, Peter Kleiweg pklei...@xs4all.nl
wrote:
Suppose the identity string is only two bytes long, I pad with
zeros to get a string of eight bytes. What should the value of
option_len be, 2 or 8?
--
Peter Kleiweg
http://pkleiweg.home.xs4all.nl/
___
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Re: [zeromq-dev] How to use zmq_getsockopt with option ZMQ_IDENTITY_FD
Thomas Rodgers schreef op de 8e dag van de louwmaand van het jaar 2015: This is an oddball API choice (and there is a bug in the implementation), in that option_value* is being used as both and input and an output parameter. The size you pass in must be be *at least* sizeof(fd_t) bytes, because it will overwrite the supplied identity string with the resulting file descriptor. The bug is, it does not check to see that the size of supplied output is sufficient to hold sizeof(fd_t), so bad things (stack/heap corruption) would happen if you actually passed option_len = 2. But option_len is used for retrieving the identity string: blob_t identity= blob_t((unsigned char*)optval_,*optvallen_); Won't I get a wrong 'blob' if I use option_len = 8? On Thu, Jan 8, 2015 at 7:26 AM, Peter Kleiweg pklei...@xs4all.nl wrote: Suppose the identity string is only two bytes long, I pad with zeros to get a string of eight bytes. What should the value of option_len be, 2 or 8? -- Peter Kleiweg http://pkleiweg.home.xs4all.nl/ ___ zeromq-dev mailing list zeromq-dev@lists.zeromq.org http://lists.zeromq.org/mailman/listinfo/zeromq-dev
Re: [zeromq-dev] How to use zmq_getsockopt with option ZMQ_IDENTITY_FD
Sorry to keep flogging this particular horse, but in re-reading the docs
for this option as I'm trying to clean it up...
NB: _option_value_ must be always big enough to hold sizeof(fd_t) bytes
no matter how small the identity length is.
There are few issues here -
Prior to commit 45c681
https://github.com/zeromq/libzmq/commit/45c68154460b5cc828cb7ac027e5407776bff2ca
there
was no validation that option_len was sufficient to hold sizeof(fd_t), so
in the 'no matter how small' case where the supplied identity length was
less than sizeof(fd_t), which is not something that is part of the public
API, so the user has to 'just know', you may get silent stack/heap
corruption.
With the the check, zmq_getsockopt(ZMQ_IDENTITY_FD, ...) will now return
EINVAL and set option_len to the minimum required size (I think this is
better than the risk of silent corruption). Now you have the following -
In the case where ZeroMQ assigns a default identity, it will have a length
of 5, and on a Posix system, the FD will be an int, sizeof(int) 5, things
are fine. On 64bit Windows however, sizeof(fd_t) = 8. If I set option_len
to 8 on call, but only have 5 bytes, the blob will be constructed with
whatever 8 bytes of data happen to be in option_value, which will then fail
to match a valid identity (std::string can contain any char, is not null
terminated). How would this option ever work in this case?
Now, say a *nix user calls zmq_setsockopt(ZMQ_IDENTITY, ...) and uses two
byte socket identities. You get the same problem trying to pass sizeof(int)
as option_len in that you create a bogus identity to check. How would this
option ever work in this case?
The only 'safe' option seems to be blindly assume that the caller passed
something at least 4 or 8 bytes long, as the code did prior to 45c681
https://github.com/zeromq/libzmq/commit/45c68154460b5cc828cb7ac027e5407776bff2ca,
but then there is NO check against buffer overrun. Default alignment would
likely save us most of the time here, but it makes my spider sense tingle
and if the caller for some reason passed a pointer into a packed struct,
they would not be happy with the result.
On Thu, Jan 8, 2015 at 9:16 AM, Thomas Rodgers rodg...@twrodgers.com
wrote:
yes.
using blob_t = std::basic_stringunsigned char;
char buf[8] = { 'f', 'o', 'o', 0, 0, 0, 0, 0 };
blob_t a(foo);
blob_t b(buf, 8);
assert(a == b); // fails
I think there is another issue with all of this. By default (IIRC) the
identity is 5 bytes, so on a 64 bit platform, the passed in identity would
never be sufficient to receive sizeof(fd_t) if fd_t was in fact defined as
a UINT_PTR. I don't have a Windows machine handy so I can't verify what
sizeof(SOCKET) returns, but as many of Window's 'handle' types are in fact
pointers, I suspect this might also be an issue when fd_t is typedef'd to
SOCKET. On Posix systems, it's fine.
On Thu, Jan 8, 2015 at 8:28 AM, Peter Kleiweg pklei...@xs4all.nl wrote:
Thomas Rodgers schreef op de 8e dag van de louwmaand van het jaar 2015:
This is an oddball API choice (and there is a bug in the
implementation),
in that option_value* is being used as both and input and an output
parameter.
The size you pass in must be be *at least* sizeof(fd_t) bytes, because
it
will overwrite the supplied identity string with the resulting file
descriptor. The bug is, it does not check to see that the size of
supplied
output is sufficient to hold sizeof(fd_t), so bad things (stack/heap
corruption) would happen if you actually passed option_len = 2.
But option_len is used for retrieving the identity string:
blob_t identity= blob_t((unsigned char*)optval_,*optvallen_);
Won't I get a wrong 'blob' if I use option_len = 8?
On Thu, Jan 8, 2015 at 7:26 AM, Peter Kleiweg pklei...@xs4all.nl
wrote:
Suppose the identity string is only two bytes long, I pad with
zeros to get a string of eight bytes. What should the value of
option_len be, 2 or 8?
--
Peter Kleiweg
http://pkleiweg.home.xs4all.nl/
___
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zeromq-dev@lists.zeromq.org
http://lists.zeromq.org/mailman/listinfo/zeromq-dev
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