Linux Security System Study NOTE 4: OpenSSL source code analysis (3)

 

BIO is an encapsulation of IO operations. The BIO abstract interface of OpenSSL can be used not only for the I/O of SSL connections, but also for non-encrypted network connections and file I/O. The source code of BIO is in the crypto/bio folder.

 

The related data structures of BIO are listed as follows.

 

BIO structure:

 

Struct bio_st

{

BIO_METHOD * method;

/* Bio, mode, argp, argi, argl, ret */

Long (* callback) (struct bio_st *, int, const char *, int, long, long );

Char * cb_arg;/* first argument for the callback */

 

Int init;

Int shutdown;

Int flags;/* extra storage */

Int retry_reason;

Int num;

Void * ptr;

Struct bio_st * next_bio;/* used by filter BIOs */

Struct bio_st * prev_bio;/* used by filter BIOs */

Int references;

Unsigned long num_read;

Unsigned long num_write;

 

CRYPTO_EX_DATA ex_data;

};

 

BIO operation structure:

 

Typedef struct bio_method_st

{

Int type;

Const char * name;

Int (* bwrite) (BIO *, const char *, int );

Int (* bread) (BIO *, char *, int );

Int (* bputs) (BIO *, const char *);

Int (* bgets) (BIO *, char *, int );

Long (* ctrl) (BIO *, int, long, void *);

Int (* create) (BIO *);

Int (* destroy) (BIO *);

Long (* callback_ctrl) (BIO *, int, bio_info_cb *);

} BIO_METHOD;

 

BIO interface types include source/receive and filter.

 

# Define BIO_TYPE_DESCRIPTOR0x0100/* socket, fd, connect or accept */

# Define BIO_TYPE_FILTER 0x0200

# Define BIO_TYPE_SOURCE_SINK 0x0400

1. Source/receipt type

 

# Define BIO_TYPE_MEM (1 | 0x0400)

# Define BIO_TYPE_FILE (2 | 0x0400)

# Define BIO_TYPE_FD (4 | 0x0400 | 0x0100)

# Define BIO_TYPE_SOCKET (5 | 0x0400 | 0x0100)

# Define BIO_TYPE_NULL (6 | 0x0400)

# Define BIO_TYPE_CONNECT (12 | 0x0400 | 0x0100)/* socket-connect */

# Define BIO_TYPE_ACCEPT (13 | 0x0400 | 0x0100)/* socket for accept */

# Define BIO_TYPE_BIO (19 | 0x0400)/* (half a) BIO pair */

# Define BIO_TYPE_DGRAM (21 | 0x0400 | 0x0100)

2. Filter Type

 

# Define BIO_TYPE_SSL (7 | 0x0200)

# Define BIO_TYPE_MD (8 | 0x0200)/* passive filter */

# Define BIO_TYPE_BUFFER (9 | 0x0200)/* filter */

# Define BIO_TYPE_CIPHER (10 | 0x0200)/* filter */

# Define BIO_TYPE_BASE64 (11 | 0x0200)/* filter */

# Define BIO_TYPE_PROXY_CLIENT (14 | 0x0200)/* client proxy BIO */

# Define BIO_TYPE_PROXY_SERVER (15 | 0x0200)/* server proxy BIO */

# Define BIO_TYPE_NBIO_TEST (16 | 0x0200)/* server proxy BIO */

# Define BIO_TYPE_NULL_FILTER (17 | 0x0200)

# Define BIO_TYPE_BER (18 | 0x0200)/* BER-> bin filter */

# Define BIO_TYPE_LINEBUFFER (20 | 0x0200)/* filter */

# Define BIO_TYPE_ASN1 (22 | 0x0200)/* filter */

# Define BIO_TYPE_COMP (23 | 0x0200)/* filter */

BIO Filter Buffer structure:

 

Typedef struct bio_f_buffer_ctx_struct

{

/* BIO * bio; * // * this is now in the BIO struct */

Int ibuf_size;/* how big is the input buffer */

Int obuf_size;/* how big is the output buffer */

 

Char * ibuf;/* the char array */

Int ibuf_len;/* how many bytes are in it */

Int ibuf_off;/* write/read offset */

 

Char * obuf;/* the char array */

Int obuf_len;/* how many bytes are in it */

Int obuf_off;/* write/read offset */

} BIO_F_BUFFER_CTX;

 

From Aegeaner's column