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[crypto] Allow for parsing of partial ASN.1 cursors 

Allow code to create a partial ASN.1 cursor containing only the type
and length bytes, so that asn1_start() may be used to determine the
length of a large ASN.1 blob without first allocating memory to hold
the entire blob.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown 2016-07-28 15:02:15 +01:00
parent 5846ce2e9e
commit 296670a648
2 changed files with 9 additions and 6 deletions
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13
src/crypto/asn1.c
View File

@ -86,6 +86,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
*
* @v cursor ASN.1 object cursor
* @v type Expected type, or ASN1_ANY
* @v extra Additional length not present within partial cursor
* @ret len Length of object body, or negative error
*
* The object cursor will be updated to point to the start of the
@ -93,7 +94,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
* the length of the object body (i.e. the number of bytes until the
* following object tag, if any) is returned.
*/
static int asn1_start ( struct asn1_cursor *cursor, unsigned int type ) {
int asn1_start ( struct asn1_cursor *cursor, unsigned int type, size_t extra ) {
unsigned int len_len;
unsigned int len;
@ -135,9 +136,9 @@ static int asn1_start ( struct asn1_cursor *cursor, unsigned int type ) {
cursor->data++;
cursor->len--;
}
if ( cursor->len < len ) {
if ( ( cursor->len + extra ) < len ) {
DBGC ( cursor, "ASN1 %p bad length %d (max %zd)\n",
cursor, len, cursor->len );
cursor, len, ( cursor->len + extra ) );
return -EINVAL_ASN1_LEN;
}
@ -158,7 +159,7 @@ static int asn1_start ( struct asn1_cursor *cursor, unsigned int type ) {
int asn1_enter ( struct asn1_cursor *cursor, unsigned int type ) {
int len;
len = asn1_start ( cursor, type );
len = asn1_start ( cursor, type, 0 );
if ( len < 0 ) {
asn1_invalidate_cursor ( cursor );
return len;
@ -185,7 +186,7 @@ int asn1_enter ( struct asn1_cursor *cursor, unsigned int type ) {
int asn1_skip_if_exists ( struct asn1_cursor *cursor, unsigned int type ) {
int len;
len = asn1_start ( cursor, type );
len = asn1_start ( cursor, type, 0 );
if ( len < 0 )
return len;
@ -242,7 +243,7 @@ int asn1_shrink ( struct asn1_cursor *cursor, unsigned int type ) {
/* Find end of object */
memcpy ( &temp, cursor, sizeof ( temp ) );
len = asn1_start ( &temp, type );
len = asn1_start ( &temp, type, 0 );
if ( len < 0 ) {
asn1_invalidate_cursor ( cursor );
return len;

2
src/include/ipxe/asn1.h
View File

@ -337,6 +337,8 @@ asn1_type ( const struct asn1_cursor *cursor ) {
return ( ( cursor->len >= sizeof ( *type ) ) ? *type : ASN1_END );
}
extern int asn1_start ( struct asn1_cursor *cursor, unsigned int type,
size_t extra );
extern int asn1_enter ( struct asn1_cursor *cursor, unsigned int type );
extern int asn1_skip_if_exists ( struct asn1_cursor *cursor,
unsigned int type );