date:20201113

Re: Server application hangs on SS_read, even when client disconnects

2020-11-13 Thread Brice André

Hello Michael,

Thanks for all those information.

I corrected your suggested point (close parent process sockets). I also
activated keepalive, with values adapted to my application.

I hope this will solve my issue, but as the problem may take several weeks
to occur, I will not know immediately if this was the origin :-)

Many thanks for your help.

Regards,
Brice


Le ven. 13 nov. 2020 à 18:52, Michael Wojcik 
a écrit :

> > From: Brice André 
> > Sent: Friday, 13 November, 2020 09:13
>
> > "Does the server parent process close its copy of the conversation
> socket?"
> > I checked in my code, but it seems that no. Is it needed?
>
> You'll want to do it, for a few reasons:
>
> - You'll be leaking descriptors in the server, and eventually it will hit
> its limit.
> - If the child process dies without cleanly closing its end of the
> conversation,
> the parent will still have an open descriptor for the socket, so the
> network stack
> won't terminate the TCP connection.
> - A related problem: If the child just closes its socket without calling
> shutdown,
> no FIN will be sent to the client system (because the parent still has its
> copy of
> the socket open). The client system will have the connection in one of the
> termination
> states (FIN_WAIT, maybe? I don't have my references handy) until it times
> out.
> - A bug in the parent process might cause it to operate on the connected
> socket,
> causing unexpected traffic on the connection.
> - All such sockets will be inherited by future child processes, and one of
> them might
> erroneously perform some operation on one of them. Obviously there could
> also be a
> security issue with this, depending on what your application does.
>
> Basically, when a descriptor is "handed off" to a child process by
> forking, you
> generally want to close it in the parent, unless it's used for parent-child
> communication. (There are some cases where the parent wants to keep it
> open for
> some reason, but they're rare.)
>
> On a similar note, if you exec a different program in the child process (I
> wasn't
> sure from your description), it's a good idea for the parent to set the
> FD_CLOEXEC
> option (with fcntl) on its listening socket and any other descriptors that
> shouldn't
> be passed along to child processes. You could close these manually in the
> child
> process between the fork and exec, but FD_CLOEXEC is often easier to
> maintain.
>
> For some applications, you might just dup2 the socket over descriptor 0 or
> descriptor 3, depending on whether the child needs access to stdio, and
> then close
> everything higher.
>
> Closing descriptors not needed by the child process is a good idea even if
> you
> don't exec, since it can prevent various problems and vulnerabilities that
> result
> from certain classes of bugs. It's a defensive measure.
>
> The best source for this sort of recommendation, in my opinion, remains W.
> Richard
> Stevens' /Advanced Programming in the UNIX Environment/. The book is old,
> and Linux
> isn't UNIX, but I don't know of any better explanation of how and why to
> do things
> in a UNIX-like OS.
>
> And my favorite source of TCP/IP information is Stevens' /TCP/IP
> Illustrated/.
>
> > May it explain my problem?
>
> In this case, I don't offhand see how it does, but I may be overlooking
> something.
>
> > I suppose that, if for some reason, the communication with the client is
> lost
> > (crash of client, loss of network, etc.) and keepalive is not enabled,
> this may
> > fully explain my problem ?
>
> It would give you those symptoms, yes.
>
> > If yes, do you have an idea of why keepalive is not enabled?
>
> The Host Requirements RFC mandates that it be disabled by default. I think
> the
> primary reasoning for that was to avoid re-establishing virtual circuits
> (e.g.
> dial-up connections) for long-running connections that had long idle
> periods.
>
> Linux may well have a kernel tunable or similar to enable TCP keepalive by
> default, but it seems to be switched off on your system. You'd have to
> consult
> the documentation for your distribution, I think.
>
> By default (again per the Host Requirements RFC), it takes quite a long
> time for
> TCP keepalive to detect a broken connection. It doesn't start probing
> until the
> connection has been idle for 2 hours, and then you have to wait for the TCP
> retransmit timer times the retransmit count to be exhausted - typically
> over 10
> minutes. Again, some OSes let you change these defaults, and some let you
> change
> them on an individual connection.
>
> --
> Michael Wojcik
>
>

## Application accessing 'ex_kusage' ##

2020-11-13 Thread Narayana, Sunil Kumar

Hi ,
We are porting our Application from  openssl 1.0.1 to openssl 
3.0. in related to this activity we require to access the variable 'ex_kusage' 
pointed by X509
But there are no set utilities available to access this variable. Only  
X509_get_key_usage Is available.

Our code for 1.0.1 is as below. Please suggest the right way to achieve this.

ASN1_BIT_STRING *usage;
662 x509->ex_kusage = 0;
663
664 if((usage=(ASN1_BIT_STRING *)X509_get_ext_d2i(x509, NID_key_usage, 
NULL, NULL)))
665 {
666 if(usage->length > 0)
667 {
668 x509->ex_kusage = usage->data[0];
669 if(usage->length > 1)
670 x509->ex_kusage |= usage->data[1] << 8;
671 }
672 else
673 x509->ex_kusage = 0;
674 ASN1_BIT_STRING_free(usage);
675 }

Regards,
Sunil


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RE: Server application hangs on SS_read, even when client disconnects

2020-11-13 Thread Michael Wojcik

> From: Brice André 
> Sent: Friday, 13 November, 2020 09:13

> "Does the server parent process close its copy of the conversation socket?"
> I checked in my code, but it seems that no. Is it needed?

You'll want to do it, for a few reasons:

- You'll be leaking descriptors in the server, and eventually it will hit its 
limit.
- If the child process dies without cleanly closing its end of the conversation,
the parent will still have an open descriptor for the socket, so the network 
stack
won't terminate the TCP connection.
- A related problem: If the child just closes its socket without calling 
shutdown,
no FIN will be sent to the client system (because the parent still has its copy 
of
the socket open). The client system will have the connection in one of the 
termination
states (FIN_WAIT, maybe? I don't have my references handy) until it times out.
- A bug in the parent process might cause it to operate on the connected socket,
causing unexpected traffic on the connection.
- All such sockets will be inherited by future child processes, and one of them 
might
erroneously perform some operation on one of them. Obviously there could also 
be a
security issue with this, depending on what your application does.

Basically, when a descriptor is "handed off" to a child process by forking, you
generally want to close it in the parent, unless it's used for parent-child
communication. (There are some cases where the parent wants to keep it open for
some reason, but they're rare.)

On a similar note, if you exec a different program in the child process (I 
wasn't
sure from your description), it's a good idea for the parent to set the 
FD_CLOEXEC
option (with fcntl) on its listening socket and any other descriptors that 
shouldn't
be passed along to child processes. You could close these manually in the child
process between the fork and exec, but FD_CLOEXEC is often easier to maintain.

For some applications, you might just dup2 the socket over descriptor 0 or
descriptor 3, depending on whether the child needs access to stdio, and then 
close
everything higher.

Closing descriptors not needed by the child process is a good idea even if you
don't exec, since it can prevent various problems and vulnerabilities that 
result
from certain classes of bugs. It's a defensive measure.

The best source for this sort of recommendation, in my opinion, remains W. 
Richard
Stevens' /Advanced Programming in the UNIX Environment/. The book is old, and 
Linux
isn't UNIX, but I don't know of any better explanation of how and why to do 
things
in a UNIX-like OS.

And my favorite source of TCP/IP information is Stevens' /TCP/IP Illustrated/.

> May it explain my problem?

In this case, I don't offhand see how it does, but I may be overlooking 
something.

> I suppose that, if for some reason, the communication with the client is lost
> (crash of client, loss of network, etc.) and keepalive is not enabled, this 
> may
> fully explain my problem ?

It would give you those symptoms, yes.

> If yes, do you have an idea of why keepalive is not enabled?

The Host Requirements RFC mandates that it be disabled by default. I think the
primary reasoning for that was to avoid re-establishing virtual circuits (e.g.
dial-up connections) for long-running connections that had long idle periods.

Linux may well have a kernel tunable or similar to enable TCP keepalive by
default, but it seems to be switched off on your system. You'd have to consult
the documentation for your distribution, I think.

By default (again per the Host Requirements RFC), it takes quite a long time for
TCP keepalive to detect a broken connection. It doesn't start probing until the
connection has been idle for 2 hours, and then you have to wait for the TCP
retransmit timer times the retransmit count to be exhausted - typically over 10
minutes. Again, some OSes let you change these defaults, and some let you change
them on an individual connection.

--
Michael Wojcik

Re: Server application hangs on SS_read, even when client disconnects

2020-11-13 Thread Brice André

Hello,

And many thanks for the answer.

"Does the server parent process close its copy of the conversation socket?"
: I checked in my code, but it seems that no. Is it needed  ? May it
explain my problem ?

" Do you have keepalives enabled?" To be honest, I did not know it was
possible to not enable them. I checked with command "netstat -tnope" and it
tells me that it is not enabled.

I suppose that, if for some reason, the communication with the client is
lost (crash of client, loss of network, etc.) and keepalive is not enabled,
this may fully explain my problem ?

If yes, do you have an idea of why keepalive is not enabled ? I thought
that by default on linux it was ?

Many thanks,
Brice


Le ven. 13 nov. 2020 à 15:43, Michael Wojcik 
a écrit :

> > From: openssl-users  On Behalf Of
> Brice André
> > Sent: Friday, 13 November, 2020 05:06
>
> > ... it seems that in some rare execution cases, the server performs a
> SSL_read,
> > the client disconnects in the meantime, and the server never detects the
> > disconnection and remains stuck in the SSL_read operation.
>
> ...
>
> > #0  0x7f836575d210 in __read_nocancel () from
> /lib/x86_64-linux-gnu/libpthread.so.0
> > #1  0x7f8365c8ccec in ?? () from
> /usr/lib/x86_64-linux-gnu/libcrypto.so.1.1
> > #2  0x7f8365c8772b in BIO_read () from
> /usr/lib/x86_64-linux-gnu/libcrypto.so.1.1
>
> So OpenSSL is in a blocking read of the socket descriptor.
>
> > tcp0  0 http://5.196.111.132:5413
> http://85.27.92.8:25856ESTABLISHED 19218/./MabeeServer
> > tcp0  0 http://5.196.111.132:5412
> http://85.27.92.8:26305ESTABLISHED 19218/./MabeeServer
>
> > From this log, I can see that I have two established connections with
> remote
> > client machine on IP 109.133.193.70. Note that it's normal to have two
> connexions
> > because my client-server protocol relies on two distinct TCP connexions.
>
> So the client has not, in fact, disconnected.
>
> When a system closes one end of a TCP connection, the stack will send a
> TCP packet
> with either the FIN or the RST flag set. (Which one you get depends on
> whether the
> stack on the closing side was holding data for the conversation which the
> application
> hadn't read.)
>
> The sockets are still in ESTABLISHED state; therefore, no FIN or RST has
> been
> received by the local stack.
>
> There are various possibilities:
>
> - The client system has not in fact closed its end of the conversation.
> Sometimes
> this happens for reasons that aren't immediately apparent; for example, if
> the
> client forked and allowed the descriptor for the conversation socket to be
> inherited
> by the child, and the child still has it open.
>
> - The client system shut down suddenly (crashed) and so couldn't send the
> FIN/RST.
>
> - There was a failure in network connectivity between the two systems, and
> consequently
> the FIN/RST couldn't be received by the local system.
>
> - The connection is in a state where the peer can't send the FIN/RST, for
> example
> because the local side's receive window is zero. That shouldn't be the
> case, since
> OpenSSL is (apparently) blocked in a receive on the connection. but as I
> don't have
> the complete picture I can't rule it out.
>
> > This let me think that the connexion on which the SSL_read is listening
> is
> > definitively dead (no more TCP keepalive)
>
> "definitely dead" doesn't have any meaning in TCP. That's not one of the
> TCP states,
> or part of the other TCP or IP metadata associated with the local port
> (which is
> what matters).
>
> Do you have keepalives enabled?
>
> > and that, for a reason I do not understand, the SSL_read keeps blocked
> into it.
>
> The reason is simple: The connection is still established, but there's no
> data to
> receive. The question isn't why SSL_read is blocking; it's why you think
> the
> connection is gone, but the stack thinks otherwise.
>
> > Note that the normal behavior of my application is : client connects,
> server
> > daemon forks a new instance,
>
> Does the server parent process close its copy of the conversation socket?
>
> --
> Michael Wojcik
>

RE: Server application hangs on SS_read, even when client disconnects

2020-11-13 Thread Michael Wojcik

> From: openssl-users  On Behalf Of Brice 
> André
> Sent: Friday, 13 November, 2020 05:06

> ... it seems that in some rare execution cases, the server performs a 
> SSL_read,
> the client disconnects in the meantime, and the server never detects the
> disconnection and remains stuck in the SSL_read operation.

...

> #0  0x7f836575d210 in __read_nocancel () from 
> /lib/x86_64-linux-gnu/libpthread.so.0
> #1  0x7f8365c8ccec in ?? () from 
> /usr/lib/x86_64-linux-gnu/libcrypto.so.1.1
> #2  0x7f8365c8772b in BIO_read () from 
> /usr/lib/x86_64-linux-gnu/libcrypto.so.1.1

So OpenSSL is in a blocking read of the socket descriptor.

> tcp0  0 http://5.196.111.132:5413  http://85.27.92.8:25856
> ESTABLISHED 19218/./MabeeServer
> tcp0  0 http://5.196.111.132:5412  http://85.27.92.8:26305
> ESTABLISHED 19218/./MabeeServer

> From this log, I can see that I have two established connections with remote
> client machine on IP 109.133.193.70. Note that it's normal to have two 
> connexions
> because my client-server protocol relies on two distinct TCP connexions.

So the client has not, in fact, disconnected.

When a system closes one end of a TCP connection, the stack will send a TCP 
packet
with either the FIN or the RST flag set. (Which one you get depends on whether 
the
stack on the closing side was holding data for the conversation which the 
application
hadn't read.)

The sockets are still in ESTABLISHED state; therefore, no FIN or RST has been
received by the local stack.

There are various possibilities:

- The client system has not in fact closed its end of the conversation. 
Sometimes
this happens for reasons that aren't immediately apparent; for example, if the
client forked and allowed the descriptor for the conversation socket to be 
inherited
by the child, and the child still has it open.

- The client system shut down suddenly (crashed) and so couldn't send the 
FIN/RST.

- There was a failure in network connectivity between the two systems, and 
consequently
the FIN/RST couldn't be received by the local system.

- The connection is in a state where the peer can't send the FIN/RST, for 
example
because the local side's receive window is zero. That shouldn't be the case, 
since
OpenSSL is (apparently) blocked in a receive on the connection. but as I don't 
have
the complete picture I can't rule it out.

> This let me think that the connexion on which the SSL_read is listening is
> definitively dead (no more TCP keepalive)

"definitely dead" doesn't have any meaning in TCP. That's not one of the TCP 
states,
or part of the other TCP or IP metadata associated with the local port (which is
what matters).

Do you have keepalives enabled?

> and that, for a reason I do not understand, the SSL_read keeps blocked into 
> it.

The reason is simple: The connection is still established, but there's no data 
to
receive. The question isn't why SSL_read is blocking; it's why you think the
connection is gone, but the stack thinks otherwise.

> Note that the normal behavior of my application is : client connects, server
> daemon forks a new instance,

Does the server parent process close its copy of the conversation socket?

--
Michael Wojcik

Server application hangs on SS_read, even when client disconnects

2020-11-13 Thread Brice André

Hello,

I have developed a client-server application with openssl and I have a
recurrent bug where, sometimes, server instance seems to be definitively
stuck in SSL_read call.

I have put more details of the problem here below, but it seems that in
some rare execution cases, the server performs a SSL_read, the client
disconnects in the meantime, and the server never detects the disconnection
and remains stuck in the SSL_read operation.

My server runs on a Debian 6.3, and my version of openssl is 1.1.0l.

Here is an extract of the code that manages the SSL connexion at server
side :

   ctx = SSL_CTX_new(SSLv23_server_method());

   BIO* bio = BIO_new_file("dhkey.pem", "r");
   if (bio == NULL) ...
   DH* ret = PEM_read_bio_DHparams(bio, NULL, NULL, NULL);
   BIO_free(bio);
   if (SSL_CTX_set_tmp_dh(ctx, ret) < 0) ...

   SSL_CTX_set_default_passwd_cb_userdata(ctx, (void*)key);
   if (SSL_CTX_use_PrivateKey_file(ctx, "server.key", SSL_FILETYPE_PEM) <=
0) ...
   if (SSL_CTX_use_certificate_file(ctx, "server.crt", SSL_FILETYPE_PEM) <=
0) ...
   if (SSL_CTX_check_private_key(ctx) == 0) ...
   SSL_CTX_set_cipher_list(ctx, "ALL");

   ssl_in = SSL_new(ctx);
   BIO* sslclient_in = BIO_new_socket(in_sock, BIO_NOCLOSE);
   SSL_set_bio(ssl_in, sslclient_in, sslclient_in);
   int r_in = SSL_accept(ssl_in);
   if (r_in != 1) ...

   ...

   /* Place where program hangs : */
   int read = SSL_read(ssl_in, &(((char*)ptr)[nb_read]), size-nb_read);

Here is the full stack-trace where the program hangs :

#0  0x7f836575d210 in __read_nocancel () from
/lib/x86_64-linux-gnu/libpthread.so.0
#1  0x7f8365c8ccec in ?? () from
/usr/lib/x86_64-linux-gnu/libcrypto.so.1.1
#2  0x7f8365c8772b in BIO_read () from
/usr/lib/x86_64-linux-gnu/libcrypto.so.1.1
#3  0x7f83659879a2 in ?? () from /usr/lib/x86_64-linux-gnu/libssl.so.1.1
#4  0x7f836598b70d in ?? () from /usr/lib/x86_64-linux-gnu/libssl.so.1.1
#5  0x7f8365989113 in ?? () from /usr/lib/x86_64-linux-gnu/libssl.so.1.1
#6  0x7f836598eff6 in ?? () from /usr/lib/x86_64-linux-gnu/libssl.so.1.1
#7  0x7f8365998dc9 in SSL_read () from
/usr/lib/x86_64-linux-gnu/libssl.so.1.1
#8  0x55b7b3e98289 in Socket::SslRead (this=0x7ffdc6131900, size=4,
ptr=0x7ffdc613066c)
at ../../Utilities/Database/Sync/server/Communication/Socket.cpp:80

Here is the result of "netstat -natp | grep " :

tcp   32  0 5.196.111.132:5412  109.133.193.70:51822
 CLOSE_WAIT  19218/./MabeeServer
tcp   32  0 5.196.111.132:5412  109.133.193.70:51696
 CLOSE_WAIT  19218/./MabeeServer
tcp   32  0 5.196.111.132:5412  109.133.193.70:51658
 CLOSE_WAIT  19218/./MabeeServer
tcp0  0 5.196.111.132:5413  85.27.92.8:25856
 ESTABLISHED 19218/./MabeeServer
tcp   32  0 5.196.111.132:5412  109.133.193.70:51818
 CLOSE_WAIT  19218/./MabeeServer
tcp   32  0 5.196.111.132:5412  109.133.193.70:51740
 CLOSE_WAIT  19218/./MabeeServer
tcp0  0 5.196.111.132:5412  85.27.92.8:26305
 ESTABLISHED 19218/./MabeeServer
tcp6   0  0 ::1:36448   ::1:5432
 ESTABLISHED 19218/./MabeeServer

>From this log, I can see that I have two established connections with
remote client machine on IP 109.133.193.70. Note that it's normal to have
two connexions because my client-server protocol relies on two distinct TCP
connexions.

>From this, I logged the result of a "tcpdump -i any -nn host 85.27.92.8"
during two days (and during those two days, my server instance remained
stuck in SSL_read...). On this log, I see no packet exchange on ports
85.27.92.8:25856 or 85.27.92.8:26305. I see some burst of packets exchanged
on other client TCP ports, but probably due to the client that performs
other requests to the server (and thus, the server that is forking new
instances with connections on other client ports).

This let me think that the connexion on which the SSL_read is listening is
definitively dead (no more TCP keepalive), and that, for a reason I do not
understand, the SSL_read keeps blocked into it.

Note that the normal behavior of my application is : client connects,
server daemon forks a new instance, communication remains a few seconds
with forked server instance, client disconnects and the forked process
finished.

Note also that normally, client performs a proper disconnection
(SSL_shutdown, etc.). But I cannot guarantee it never interrupts on a more
abrupt way (connection lost, client crash, etc.).

Any advice on what is going wrong ?

Many thanks,

Brice

Re: Server application hangs on SS_read, even when client disconnects

## Application accessing 'ex_kusage' ##

RE: Server application hangs on SS_read, even when client disconnects

Re: Server application hangs on SS_read, even when client disconnects

RE: Server application hangs on SS_read, even when client disconnects

Server application hangs on SS_read, even when client disconnects

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