MPILIB: Provide a function to read raw data into an MPI

Provide a function to read raw data of a predetermined size into an MPI rather than expecting the size to be encoded within the data. The data is assumed to represent an unsigned integer, and the resulting MPI will be positive. The function looks like this: MPI mpi_read_raw_data(const void *, size_t); This is useful for reading ASN.1 integer primitives where the length is encoded in the ASN.1 metadata. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

MPILIB: Provide a function to read raw data into an MPI
Provide a function to read raw data of a predetermined size into an MPI rather than expecting the size to be encoded within the data. The data is assumed to represent an unsigned integer, and the resulting MPI will be positive. The function looks like this: MPI mpi_read_raw_data(const void *, size_t); This is useful for reading ASN.1 integer primitives where the length is encoded in the ASN.1 metadata. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
David Howells · Rusty Russell · Eric Lee · Eric Lee
1 parent 42d5ec27f8
Showing 2 changed files with 56 additions and 0 deletions Side-by-side Diff
include/linux/mpi.h
lib/mpi/mpicoder.c
@@ -76,6 +76,7 @@
  
 /*-- mpicoder.c --*/
 MPI do_encode_md(const void *sha_buffer, unsigned nbits);
+MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes);
 MPI mpi_read_from_buffer(const void *buffer, unsigned *ret_nread);
 int mpi_fromstr(MPI val, const char *str);
 u32 mpi_get_keyid(MPI a, u32 *keyid);
@@ -18,9 +18,64 @@
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  */
  
+#include <linux/bitops.h>
+#include <asm-generic/bitops/count_zeros.h>
 #include "mpi-internal.h"
  
 #define MAX_EXTERN_MPI_BITS 16384
+
+/**
+ * mpi_read_raw_data - Read a raw byte stream as a positive integer
+ * @xbuffer: The data to read
+ * @nbytes: The amount of data to read
+ */
+MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes)
+{
+	const uint8_t *buffer = xbuffer;
+	int i, j;
+	unsigned nbits, nlimbs;
+	mpi_limb_t a;
+	MPI val = NULL;
+
+	while (nbytes >= 0 && buffer[0] == 0) {
+		buffer++;
+		nbytes--;
+	}
+
+	nbits = nbytes * 8;
+	if (nbits > MAX_EXTERN_MPI_BITS) {
+		pr_info("MPI: mpi too large (%u bits)\n", nbits);
+		return NULL;
+	}
+	if (nbytes > 0)
+		nbits -= count_leading_zeros(buffer[0]);
+	else
+		nbits = 0;
+
+	nlimbs = (nbytes + BYTES_PER_MPI_LIMB - 1) / BYTES_PER_MPI_LIMB;
+	val = mpi_alloc(nlimbs);
+	if (!val)
+		return NULL;
+	val->nbits = nbits;
+	val->sign = 0;
+	val->nlimbs = nlimbs;
+
+	if (nbytes > 0) {
+		i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
+		i %= BYTES_PER_MPI_LIMB;
+		for (j = nlimbs; j > 0; j--) {
+			a = 0;
+			for (; i < BYTES_PER_MPI_LIMB; i++) {
+				a <<= 8;
+				a |= *buffer++;
+			}
+			i = 0;
+			val->d[j - 1] = a;
+		}
+	}
+	return val;
+}
+EXPORT_SYMBOL_GPL(mpi_read_raw_data);
  
 MPI mpi_read_from_buffer(const void *xbuffer, unsigned *ret_nread)
 {
...	...	@@ -76,6 +76,7 @@
76	76
77	77	/-- mpicoder.c --/
78	78	MPI do_encode_md(const void *sha_buffer, unsigned nbits);
	79	+MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes);
79	80	MPI mpi_read_from_buffer(const void buffer, unsigned ret_nread);
80	81	int mpi_fromstr(MPI val, const char *str);
81	82	u32 mpi_get_keyid(MPI a, u32 *keyid);
...	...	@@ -18,9 +18,64 @@
18	18	* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
19	19	*/
20	20
	21	+#include <linux/bitops.h>
	22	+#include <asm-generic/bitops/count_zeros.h>
21	23	#include "mpi-internal.h"
22	24
23	25	#define MAX_EXTERN_MPI_BITS 16384
	26	+
	27	+/**
	28	+ * mpi_read_raw_data - Read a raw byte stream as a positive integer
	29	+ * @xbuffer: The data to read
	30	+ * @nbytes: The amount of data to read
	31	+ */
	32	+MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes)
	33	+{
	34	+ const uint8_t *buffer = xbuffer;
	35	+ int i, j;
	36	+ unsigned nbits, nlimbs;
	37	+ mpi_limb_t a;
	38	+ MPI val = NULL;
	39	+
	40	+ while (nbytes >= 0 && buffer[0] == 0) {
	41	+ buffer++;
	42	+ nbytes--;
	43	+ }
	44	+
	45	+ nbits = nbytes * 8;
	46	+ if (nbits > MAX_EXTERN_MPI_BITS) {
	47	+ pr_info("MPI: mpi too large (%u bits)\n", nbits);
	48	+ return NULL;
	49	+ }
	50	+ if (nbytes > 0)
	51	+ nbits -= count_leading_zeros(buffer[0]);
	52	+ else
	53	+ nbits = 0;
	54	+
	55	+ nlimbs = (nbytes + BYTES_PER_MPI_LIMB - 1) / BYTES_PER_MPI_LIMB;
	56	+ val = mpi_alloc(nlimbs);
	57	+ if (!val)
	58	+ return NULL;
	59	+ val->nbits = nbits;
	60	+ val->sign = 0;
	61	+ val->nlimbs = nlimbs;
	62	+
	63	+ if (nbytes > 0) {
	64	+ i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
	65	+ i %= BYTES_PER_MPI_LIMB;
	66	+ for (j = nlimbs; j > 0; j--) {
	67	+ a = 0;
	68	+ for (; i < BYTES_PER_MPI_LIMB; i++) {
	69	+ a <<= 8;
	70	+ a \|= *buffer++;
	71	+ }
	72	+ i = 0;
	73	+ val->d[j - 1] = a;
	74	+ }
	75	+ }
	76	+ return val;
	77	+}
	78	+EXPORT_SYMBOL_GPL(mpi_read_raw_data);
24	79
25	80	MPI mpi_read_from_buffer(const void xbuffer, unsigned ret_nread)
26	81	{