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Add a generic sk_msg layer, and convert current sockmap and later
kTLS over to make use of it. While sk_buff handles network packet
representation from netdevice up to socket, sk_msg handles data
representation from application to socket layer.
This means that sk_msg framework spans across ULP users in the
kernel, and enables features such as introspection or filtering
of data with the help of BPF programs that operate on this data
structure.
Latter becomes in particular useful for kTLS where data encryption
is deferred into the kernel, and as such enabling the kernel to
perform L7 introspection and policy based on BPF for TLS connections
where the record is being encrypted after BPF has run and came to
a verdict. In order to get there, first step is to transform open
coding of scatter-gather list handling into a common core framework
that subsystems can use.
The code itself has been split and refactored into three bigger
pieces: i) the generic sk_msg API which deals with managing the
scatter gather ring, providing helpers for walking and mangling,
transferring application data from user space into it, and preparing
it for BPF pre/post-processing, ii) the plain sock map itself
where sockets can be attached to or detached from; these bits
are independent of i) which can now be used also without sock
map, and iii) the integration with plain TCP as one protocol
to be used for processing L7 application data (later this could
e.g. also be extended to other protocols like UDP). The semantics
are the same with the old sock map code and therefore no change
of user facing behavior or APIs. While pursuing this work it
also helped finding a number of bugs in the old sockmap code
that we've fixed already in earlier commits. The test_sockmap
kselftest suite passes through fine as well.
Joint work with John.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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This patch introduces a utility for parsing application layer protocol
messages in a TCP stream. This is a generalization of the mechanism
implemented of Kernel Connection Multiplexor.
The API includes a context structure, a set of callbacks, utility
functions, and a data ready function.
A stream parser instance is defined by a strparse structure that
is bound to a TCP socket. The function to initialize the structure
is:
int strp_init(struct strparser *strp, struct sock *csk,
struct strp_callbacks *cb);
csk is the TCP socket being bound to and cb are the parser callbacks.
The upper layer calls strp_tcp_data_ready when data is ready on the lower
socket for strparser to process. This should be called from a data_ready
callback that is set on the socket:
void strp_tcp_data_ready(struct strparser *strp);
A parser is bound to a TCP socket by setting data_ready function to
strp_tcp_data_ready so that all receive indications on the socket
go through the parser. This is assumes that sk_user_data is set to
the strparser structure.
There are four callbacks.
- parse_msg is called to parse the message (returns length or error).
- rcv_msg is called when a complete message has been received
- read_sock_done is called when data_ready function exits
- abort_parser is called to abort the parser
The input to parse_msg is an skbuff which contains next message under
construction. The backend processing of parse_msg will parse the
application layer protocol headers to determine the length of
the message in the stream. The possible return values are:
>0 : indicates length of successfully parsed message
0 : indicates more data must be received to parse the message
-ESTRPIPE : current message should not be processed by the
kernel, return control of the socket to userspace which
can proceed to read the messages itself
other < 0 : Error is parsing, give control back to userspace
assuming that synchronzation is lost and the stream
is unrecoverable (application expected to close TCP socket)
In the case of error return (< 0) strparse will stop the parser
and report and error to userspace. The application must deal
with the error. To handle the error the strparser is unbound
from the TCP socket. If the error indicates that the stream
TCP socket is at recoverable point (ESTRPIPE) then the application
can read the TCP socket to process the stream. Once the application
has dealt with the exceptions in the stream, it may again bind the
socket to a strparser to continue data operations.
Note that ENODATA may be returned to the application. In this case
parse_msg returned -ESTRPIPE, however strparser was unable to maintain
synchronization of the stream (i.e. some of the message in question
was already read by the parser).
strp_pause and strp_unpause are used to provide flow control. For
instance, if rcv_msg is called but the upper layer can't immediately
consume the message it can hold the message and pause strparser.
Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Daniel Borkmann
Tom Herbert