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PK parse/write: support keylen=0 correctly

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A 0-length buffer for the key is a legitimate edge case. Ensure that
it works, even with buf=NULL. Document the key and keylen parameters.

There are already test cases for parsing an empty buffer. A subsequent
commit will add tests for writing to an empty buffer.
This commit is contained in:
Gilles Peskine 2018-12-19 17:03:28 +01:00
parent 1f19fa6f62
commit 159171b72a
3 changed files with 39 additions and 25 deletions
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34
include/mbedtls/pk.h
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@ -530,9 +530,13 @@ mbedtls_pk_type_t mbedtls_pk_get_type( const mbedtls_pk_context *ctx );
* \brief Parse a private key in PEM or DER format * \brief Parse a private key in PEM or DER format
* *
* \param ctx key to be initialized * \param ctx key to be initialized
* \param key input buffer * \param key Input buffer to parse.
* \param keylen size of the buffer * The buffer must contain the input exactly, with no
* (including the terminating null byte for PEM data) * extra trailing material. For PEM, the buffer must
* contain a null-terminated string.
* \param keylen Size of \b key in bytes.
* For PEM data, this includes the terminating null byte,
* so \p keylen must be equal to `strlen(key) + 1`.
* \param pwd password for decryption (optional) * \param pwd password for decryption (optional)
* \param pwdlen size of the password * \param pwdlen size of the password
* *
@ -553,9 +557,13 @@ int mbedtls_pk_parse_key( mbedtls_pk_context *ctx,
* \brief Parse a public key in PEM or DER format * \brief Parse a public key in PEM or DER format
* *
* \param ctx key to be initialized * \param ctx key to be initialized
* \param key input buffer * \param key Input buffer to parse.
* \param keylen size of the buffer * The buffer must contain the input exactly, with no
* (including the terminating null byte for PEM data) * extra trailing material. For PEM, the buffer must
* contain a null-terminated string.
* \param keylen Size of \b key in bytes.
* For PEM data, this includes the terminating null byte,
* so \p keylen must be equal to `strlen(key) + 1`.
* *
* \note On entry, ctx must be empty, either freshly initialised * \note On entry, ctx must be empty, either freshly initialised
* with mbedtls_pk_init() or reset with mbedtls_pk_free(). If you need a * with mbedtls_pk_init() or reset with mbedtls_pk_free(). If you need a
@ -643,9 +651,10 @@ int mbedtls_pk_write_pubkey_der( mbedtls_pk_context *ctx, unsigned char *buf, si
/** /**
* \brief Write a public key to a PEM string * \brief Write a public key to a PEM string
* *
* \param ctx public key to write away * \param ctx Context containing the public key to write.
* \param buf buffer to write to * \param buf Buffer to write to. The output includes a
* \param size size of the buffer * terminating null byte.
* \param size Size of the buffer in bytes.
* *
* \return 0 if successful, or a specific error code * \return 0 if successful, or a specific error code
*/ */
@ -654,9 +663,10 @@ int mbedtls_pk_write_pubkey_pem( mbedtls_pk_context *ctx, unsigned char *buf, si
/** /**
* \brief Write a private key to a PKCS#1 or SEC1 PEM string * \brief Write a private key to a PKCS#1 or SEC1 PEM string
* *
* \param ctx private to write away * \param ctx Context containing the private key to write.
* \param buf buffer to write to * \param buf Buffer to write to. The output includes a
* \param size size of the buffer * terminating null byte.
* \param size Size of the buffer in bytes.
* *
* \return 0 if successful, or a specific error code * \return 0 if successful, or a specific error code
*/ */

22
library/pkparse.c
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@ -1170,15 +1170,16 @@ int mbedtls_pk_parse_key( mbedtls_pk_context *pk,
#endif #endif
PK_VALIDATE_RET( pk != NULL ); PK_VALIDATE_RET( pk != NULL );
PK_VALIDATE_RET( key != NULL || keylen == 0 ); if( keylen == 0 )
PK_VALIDATE_RET( pwd != NULL || pwdlen == 0 ); return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT );
PK_VALIDATE_RET( key != NULL );
#if defined(MBEDTLS_PEM_PARSE_C) #if defined(MBEDTLS_PEM_PARSE_C)
mbedtls_pem_init( &pem ); mbedtls_pem_init( &pem );
#if defined(MBEDTLS_RSA_C) #if defined(MBEDTLS_RSA_C)
/* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */ /* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */
if( keylen == 0 || key[keylen - 1] != '\0' ) if( key[keylen - 1] != '\0' )
ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT; ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT;
else else
ret = mbedtls_pem_read_buffer( &pem, ret = mbedtls_pem_read_buffer( &pem,
@ -1209,7 +1210,7 @@ int mbedtls_pk_parse_key( mbedtls_pk_context *pk,
#if defined(MBEDTLS_ECP_C) #if defined(MBEDTLS_ECP_C)
/* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */ /* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */
if( keylen == 0 || key[keylen - 1] != '\0' ) if( key[keylen - 1] != '\0' )
ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT; ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT;
else else
ret = mbedtls_pem_read_buffer( &pem, ret = mbedtls_pem_read_buffer( &pem,
@ -1239,7 +1240,7 @@ int mbedtls_pk_parse_key( mbedtls_pk_context *pk,
#endif /* MBEDTLS_ECP_C */ #endif /* MBEDTLS_ECP_C */
/* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */ /* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */
if( keylen == 0 || key[keylen - 1] != '\0' ) if( key[keylen - 1] != '\0' )
ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT; ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT;
else else
ret = mbedtls_pem_read_buffer( &pem, ret = mbedtls_pem_read_buffer( &pem,
@ -1262,7 +1263,7 @@ int mbedtls_pk_parse_key( mbedtls_pk_context *pk,
#if defined(MBEDTLS_PKCS12_C) || defined(MBEDTLS_PKCS5_C) #if defined(MBEDTLS_PKCS12_C) || defined(MBEDTLS_PKCS5_C)
/* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */ /* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */
if( keylen == 0 || key[keylen - 1] != '\0' ) if( key[keylen - 1] != '\0' )
ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT; ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT;
else else
ret = mbedtls_pem_read_buffer( &pem, ret = mbedtls_pem_read_buffer( &pem,
@ -1300,9 +1301,6 @@ int mbedtls_pk_parse_key( mbedtls_pk_context *pk,
{ {
unsigned char *key_copy; unsigned char *key_copy;
if( keylen == 0 )
return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT );
if( ( key_copy = mbedtls_calloc( 1, keylen ) ) == NULL ) if( ( key_copy = mbedtls_calloc( 1, keylen ) ) == NULL )
return( MBEDTLS_ERR_PK_ALLOC_FAILED ); return( MBEDTLS_ERR_PK_ALLOC_FAILED );
@ -1387,13 +1385,15 @@ int mbedtls_pk_parse_public_key( mbedtls_pk_context *ctx,
#endif #endif
PK_VALIDATE_RET( ctx != NULL ); PK_VALIDATE_RET( ctx != NULL );
if( keylen == 0 )
return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT );
PK_VALIDATE_RET( key != NULL || keylen == 0 ); PK_VALIDATE_RET( key != NULL || keylen == 0 );
#if defined(MBEDTLS_PEM_PARSE_C) #if defined(MBEDTLS_PEM_PARSE_C)
mbedtls_pem_init( &pem ); mbedtls_pem_init( &pem );
#if defined(MBEDTLS_RSA_C) #if defined(MBEDTLS_RSA_C)
/* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */ /* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */
if( keylen == 0 || key[keylen - 1] != '\0' ) if( key[keylen - 1] != '\0' )
ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT; ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT;
else else
ret = mbedtls_pem_read_buffer( &pem, ret = mbedtls_pem_read_buffer( &pem,
@ -1424,7 +1424,7 @@ int mbedtls_pk_parse_public_key( mbedtls_pk_context *ctx,
#endif /* MBEDTLS_RSA_C */ #endif /* MBEDTLS_RSA_C */
/* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */ /* Avoid calling mbedtls_pem_read_buffer() on non-null-terminated string */
if( keylen == 0 || key[keylen - 1] != '\0' ) if( key[keylen - 1] != '\0' )
ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT; ret = MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT;
else else
ret = mbedtls_pem_read_buffer( &pem, ret = mbedtls_pem_read_buffer( &pem,

8
library/pkwrite.c
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@ -186,7 +186,9 @@ int mbedtls_pk_write_pubkey_der( mbedtls_pk_context *key, unsigned char *buf, si
const char *oid; const char *oid;
PK_VALIDATE_RET( key != NULL ); PK_VALIDATE_RET( key != NULL );
PK_VALIDATE_RET( buf != NULL || size == 0 ); if( size == 0 )
return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
PK_VALIDATE_RET( buf != NULL );
c = buf + size; c = buf + size;
@ -236,7 +238,9 @@ int mbedtls_pk_write_key_der( mbedtls_pk_context *key, unsigned char *buf, size_
size_t len = 0; size_t len = 0;
PK_VALIDATE_RET( key != NULL ); PK_VALIDATE_RET( key != NULL );
PK_VALIDATE_RET( buf != NULL || size == 0 ); if( size == 0 )
return( MBEDTLS_ERR_ASN1_BUF_TOO_SMALL );
PK_VALIDATE_RET( buf != NULL );
c = buf + size; c = buf + size;