Commit 558c1a4 ("[tcp] Improve robustness in the presence of duplicated
received packets") introduced a regression in that an old duplicate
ACK received while in the ESTABLISHED state would pass through normal
ACK processing, including updating tcp->snd_seq.

Fix by ensuring that ACK processing ignores all duplicate ACKs.

All TCP errors or unusual events should now generate a debugging
message at DBGLVL_LOG, with enough information (SEQ and ACK numbers)
to be able to identify the corresponding packet (or missing packet) in
a network trace from the remote end.

This makes it possible to leave TCP debugging enabled in order to see
interesting TCP events, without flooding the console with at least one
message per packet.

In order to construct outgoing link-layer frames or parse incoming
ones properly, some protocols (such as 802.11) need more state than is
available in the existing variables passed to the link-layer protocol
handlers. To remedy this, add struct net_device *netdev as the first
argument to each of these functions, so that more information can be
fetched from the link layer-private part of the network device.

Updated all three call sites (netdevice.c, efi_snp.c, pxe_undi.c) and
both implementations (ethernet.c, ipoib.c) of ll_protocol to use the
new argument.

Signed-off-by: Michael Brown <mcb30@etherboot.org>

gPXE responds to duplicated ACKs with an immediate retransmission,
which can lead to a sorceror's apprentice syndrome.  It also responds
to out-of-range (or old duplicate) ACKs with a RST, which can cause
valid connections to be dropped.

Fix the sorceror's apprentice syndrome by leaving the retransmission
timer running (and so inhibiting the immediate retransmission) when we
receive a potential duplicate ACK.  This seems to match the behaviour
of Linux observed via wireshark traces.

Fix the RST issue by sending RST only on out-of-range ACKs that occur
before the connection is fully established, as per RFC 793.

These problems were exposed during development of the 802.11 wireless
link layer; the 802.11 protocol has a failure mode that can easily
cause duplicated packets.  The fixes were tested in a controlled way
by faking large numbers of duplicated packets in the rtl8139 driver.

Originally-fixed-by: Joshua Oreman <oremanj@rwcr.net>

Signed-off-by: Michael Brown <mcb30@etherboot.org>

This provides a mechanism for using arbitrarily-named variables within
gPXE, using the existing syntax for settings.

If the ProxyDHCPOFFER already includes PXE options (i.e. option 60 is
set to "PXEClient" and option 43 is present) then assume that the
ProxyDHCPREQUEST can be sent to port 67, rather than port 4011.  This
is a reasonable assumption, since in that case the ProxyDHCP server
has already demonstrated by responding to the DHCPDISCOVER that it is
listening on port 67.  (If the ProxyDHCP server were not listening on
port 67, then the standard DHCP server would have been configured to
respond with option 60 set to "PXEClient" but no option 43 present.)

The PXE specification is ambiguous on this point; the specified
behaviour covers only the cases in which option 43 is *not* present in
the ProxyDHCPOFFER.  In these cases, we will continue to send the
ProxyDHCPREQUEST to port 4011.

This change is required in order to allow us to interoperate with
dnsmasq, which listens only on port 67.  (dnsmasq relies on
unspecified behaviour of the Intel PXE stack, which it seems will
retain the ProxyDHCPOFFER as an options source and never issue a
ProxyDHCPREQUEST, thereby enabling dnsmasq to omit listening on port
4011.)

IBM Tivoli PXE Server 5.1.0.3 is reported to send trailing garbage
bytes at the end of the OACK packet, which causes gPXE to reject the
packet and abort the TFTP transfer.

Work around the problem by processing as much as possible of the OACK,
and treating name/value parsing errors as non-fatal.

Reported-by: Shao Miller <Shao.Miller@yrdsb.edu.on.ca>

We currently send all boot server discovery requests to port 4011.
Section 2.2.1 of the PXE spec states that boot server discovery
packets should be "sent broadcast (port 67), multicast (port 4011), or
unicast (port 4011)".  Adjust our behaviour so that any boot server
discovery packets that are sent to the broadcast address are directed
to port 67 rather than port 4011.

This is required for operation with dnsmasq as a PXE server, since
dnsmasq listens only on port 67, and relies upon this (specified)
behaviour.

This change may break some setups using the (itself very broken) Linux
PXE server from kano.org.uk.  This server will, in its default
configuration, listen only on port 4011.  It never constructs a boot
server list (PXE_BOOT_SERVERS, option 43.8), and uses the wrong
definitions for the discovery control bits (PXE_DISCOVERY_CONTROL,
option 43.6).  The upshot is that it will always instruct the client
to perform multicast and broadcast discovery only.  In setups lacking
a valid multicast route on the server side, this used to work because
gPXE would eventually give up on the (non-responsive) multicast
address and send a broadcast request to port 4011, which the Linux PXE
server would respond to.  Now that gPXE correctly sends this broadcast
request to port 67 instead, it is never seen by the Linux PXE server,
and the boot fails.  The fix is to either (a) set up a multicast route
correctly on the server side before starting the PXE server, or (b)
edit /etc/pxe.conf to contain the server's unicast address in the
"multicast_address" field (a hack that happens to work).

Suggested-by: Simon Kelley <simon@thekelleys.org.uk>

This prevents gPXE from wasting time attempting to contact a ProxyDHCP
server on port 4011 if the DHCP response already contains the relevant
PXE options.  This behaviour is hinted at (though not explicitly
specified) in the PXE spec, and seems to match what the Intel client
does.

Suggested-by: Simon Kelley <simon@thekelleys.org.uk>

Add FILE_LICENCE declarations to almost all files that make up the
various standard builds of gPXE.

Allow options with dedicated BOOTP fields to fall back to using the
equivalent DHCP option if the relevant field is empty.

When handling a redirection event, we need to close the existing
connection before opening the new connection.

Suggested-by: Bill Lortz <Bill.Lortz@premier.org>

Eliminate the potential for mismatches between table names and the
table entry data type by incorporating the data type into the
definition of the table, rather than specifying it explicitly in each
table accessor method.

Intel's C compiler (icc) chokes on the zero-length arrays that we
currently use as part of the mechanism for accessing linker table
entries.  Abstract away the zero-length arrays, to make a port to icc
easier.

Introduce macros such as for_each_table_entry() to simplify the common
case of iterating over all entries in a linker table.

Represent table names as #defined string constants rather than
unquoted literals; this avoids visual confusion between table names
and C variable or type names, and also allows us to force a
compilation error in the event of incorrect table names.

Some firewall devices seem to regard SYN,PSH as an invalid flag
combination and reject the packet.  Fix by setting PSH only if SYN is
not set.

Reported-by: DSE Incorporated <dseinc@gmail.com>

Avoid passing credentials in the iBFT that were available but not
required for login.  This works around a problem in the Microsoft
iSCSI initiator, which will refuse to initiate sessions if the CHAP
password is fewer than 12 characters, even if the target ends up not
asking for CHAP authentication.

It is a programming error, not a runtime error, if we attempt to use
block ciphers with an incorrect blocksize, so use an assert() rather
than an error status return.

The various types of cryptographic algorithm are fundamentally
different, and it was probably a mistake to try to handle them via a
single common type.

pubkey_algorithm is a placeholder type for now.

Although the nature of the hack is essentially unchanged, this allows
us to remove the hardcoded assumption in tls.c that the RX cipher is
AES.

This change makes it possible to break the PXE-chaining infinite loop
even when restricted to a Windows DHCP server.

Send authentication information if the username is present, even if
the password is empty.

The documentation in xfer.h and xfer.c does not say that the metadata
parameter is optional in calls such as xfer_deliver_iob_meta() and the
deliver_iob() method.  However, some code in net/ is prepared to
accept a NULL pointer, and xfer_deliver_as_iob() passes a NULL pointer
directly to the deliver_iob() method.

Fix this mess of conflicting assumptions by making everything assume
that the metadata parameter is mandatory, and fixing
xfer_deliver_as_iob() to pass in a dummy metadata structure (as is
already done in xfer_deliver_iob()).

Use our own, more robust, ASN.1 parsing routines to extract the RSA
public key from a server certificate.  Remove the now-unused AXTLS
ASN.1 parser.

Various combinations of options 43.6, 43.7 and 43.8 dictate which
servers we send Boot Server Discovery requests to, and which servers
we should accept responses from.  Obey these options, and remove the
explicit specification of a single Boot Server from start_pxebs() and
dependent functions.

There are many functions that take ownership of the I/O buffer they
are passed as a parameter.  The caller should not retain a pointer to
the I/O buffer.  Use iob_disown() to automatically nullify the
caller's pointer, e.g.:

    xfer_deliver_iob ( xfer, iob_disown ( iobuf ) );

This will ensure that iobuf is set to NULL for any code after the call
to xfer_deliver_iob().

iob_disown() is currently used only in places where it simplifies the
code, by avoiding an extra line explicitly setting the I/O buffer
pointer to NULL.  It should ideally be used with each call to any
function that takes ownership of an I/O buffer.  (The SSA
optimisations will ensure that use of iob_disown() gets optimised away
in cases where the caller makes no further use of the I/O buffer
pointer anyway.)

If gcc ever introduces an __attribute__((free)), indicating that use
of a function argument after a function call should generate a
warning, then we should use this to identify all applicable function
call sites, and add iob_disown() as necessary.

A TFTP DATA packet with a block number of zero (representing a
negative offset within the file) could potentially cause problems.
Fixed by explicitly rejecting such packets.

Identified by Stefan Hajnoczi <stefanha@gmail.com>.

The DHCP client code now implements only the mechanism of the DHCP and
PXE Boot Server protocols.  Boot Server Discovery can be initiated
manually using the "pxebs" command.  The menuing code is separated out
into a user-level function on a par with boot_root_path(), and is
entered in preference to a normal filename boot if the DHCP vendor
class is "PXEClient" and the PXE boot menu option exists.

Try to qualify relative names in the DNS resolver using the DHCP Domain
Name.  For example:

  DHCP Domain Name: etherboot.org
  (Relative) Name: www

yields:

  www.etherboot.org

Only names with no dots ('.') will be modified.  A name with one or more
dots is unchanged.

pxe_tftp.c assumes that the first seek on its data-transfer interface
represents the block size.  Apart from being an ugly hack, this will
also screw up file size calculation for files smaller than one block.

The proper solution would be to extend the data-transfer interface to
support the reporting of stat()-like data.  This is not going to
happen until the cost of adding interface methods is reduced (a fix I
have planned since June 2008).

In the meantime, abuse the xfer_window() method to return the block
size, since it is not being used for anything else and is vaguely
justifiable.

Astonishingly, having returned the incorrect TFTP blocksize via
PXENV_TFTP_OPEN for almost a year seems not to have affected any of
the test cases run during that time; this bug was found only when
someone tried running the heavily-patched version of pxegrub found in
OpenSolaris.

PXE dictates a mechanism for boot menuing, involving prompting the
user with a variable message, waiting for a predefined keypress,
displaying a boot menu, and waiting for a selection.

This breaks the currently desirable abstraction that DHCP is a process
that can happen in the background without any user interaction.

Remove the lazy assumption that ProxyDHCP == "DHCP with option 60 set
to PXEClient", and explicitly separate the notion of ProxyDHCP from
the notion of packets containing PXE options.

It is possible to configure a DHCP server to hand out PXE options
without a ProxyDHCP server present.  This requires setting option 60
to "PXEClient", which will cause gPXE to attempt ProxyDHCP.

We assume in several places that dhcp->proxydhcpack is set to the
DHCPACK packet containing option 60 set to "PXEClient".  When we
transition into ProxyDHCPREQUEST, set dhcp->proxydhcpack=dhcp->dhcpack
so that this assumption holds true.

We ought to rename several references to "proxydhcp" to something more
accurate, such as "pxedhcp".  Treating a single DHCP response as
potentially both DHCPOFFER and ProxyDHCPOFFER does make the code
smaller, but the variable names get confusing.

Pick out the first boot menu item from the boot menu (option 43.9) and
pass it to the boot server as the boot menu item (option 43.71).

Also improve DHCP debug messages to include more details of the
packets being transmitted.

Apparently this can cause a major speedup on some iSCSI targets, which
will otherwise wait for a timer to expire before responding.  It
doesn't seem to hurt other simple TCP test cases (e.g. HTTP
downloads).

Problem and solution identified by Shiva Shankar <802.11e@gmail.com>

Some PXE configurations require us to perform a third DHCP transaction
(in addition to the real DHCP transaction and the ProxyDHCP
transaction) in order to retrieve information from a "Boot Server".

This is an experimental implementation, since the actual behaviour is
not well specified in the PXE spec.

When sending to a multicast address, it may be necessary to specify
the source address explicitly, since the multicast destination address
does not provide enough information to deduce the source address via
the miniroute table.

Allow the source address specified via the data-xfer metadata to be
passed down through the TCP/IP stack to the IPv4 layer, which can use
it as a default source address.

eth_mc_hash() was missing a return within a switch statement, and so
always falling through to the default case and returning failure.

Move all the DHCP state transition logic into a single function
dhcp_next_state().  This will make it easier to add support for PXE
Boot Servers, since it abstracts away the difference between "mark
DHCP as complete" and "transition to boot server discovery".

The Linux PXE server (http://www.kano.org.uk/projects/pxe) does not
set the server identifier in its ProxyDHCP responses.  If the server
ID is missing, do not treat this as an error.

This resolves the "vague and unsettling memory" mentioned in commit
fdb8481d ("[dhcp] Verify server identifier on ProxyDHCPACKs").

Note that we already accept ProxyDHCPOFFERs without a server
identifier; they get treated as potential BOOTP packets.