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Merge pull request #3935 from paul-elliott-arm/fix_pem_write_2_16

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Backport 2.16: Remove Extraneous bytes from buffer post pem write
This commit is contained in:
Gilles Peskine 2020-12-08 12:31:47 +01:00 committed by GitHub
commit 9e8acb6861
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GPG Key ID: 4AEE18F83AFDEB23
4 changed files with 42 additions and 5 deletions
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6
ChangeLog.d/clean_pem_buffers.txt Normal file
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@ -0,0 +1,6 @@
Bugfix
* In PEM writing functions, fill the trailing part of the buffer with null
bytes. This guarantees that the corresponding parsing function can read
the buffer back, which was the case for mbedtls_x509write_{crt,csr}_pem
until this property was inadvertently broken in Mbed TLS 2.19.0.
Fixes #3682.

4
library/pem.c
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@ -508,8 +508,12 @@ int mbedtls_pem_write_buffer( const char *header, const char *footer,
*p++ = '\0';
*olen = p - buf;
/* Clean any remaining data previously written to the buffer */
memset( buf + *olen, 0, buf_len - *olen );
mbedtls_free( encode_buf );
return( 0 );
}
#endif /* MBEDTLS_PEM_WRITE_C */
#endif /* MBEDTLS_PEM_PARSE_C || MBEDTLS_PEM_WRITE_C */

22
tests/suites/test_suite_pkwrite.function
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@ -17,7 +17,7 @@ void pk_write_pubkey_check( char * key_file )
unsigned char check_buf[5000];
int ret;
FILE *f;
size_t ilen;
size_t ilen, pem_len, buf_index;
memset( buf, 0, sizeof( buf ) );
memset( check_buf, 0, sizeof( check_buf ) );
@ -28,12 +28,20 @@ void pk_write_pubkey_check( char * key_file )
ret = mbedtls_pk_write_pubkey_pem( &key, buf, sizeof( buf ));
TEST_ASSERT( ret == 0 );
pem_len = strlen( (char *) buf );
// check that the rest of the buffer remains clear
for( buf_index = pem_len; buf_index < sizeof( buf ); ++buf_index )
{
TEST_ASSERT( buf[buf_index] == 0 );
}
f = fopen( key_file, "r" );
TEST_ASSERT( f != NULL );
ilen = fread( check_buf, 1, sizeof( check_buf ), f );
fclose( f );
TEST_ASSERT( ilen == strlen( (char *) buf ) );
TEST_ASSERT( ilen == pem_len );
TEST_ASSERT( memcmp( (char *) buf, (char *) check_buf, ilen ) == 0 );
exit:
@ -49,7 +57,7 @@ void pk_write_key_check( char * key_file )
unsigned char check_buf[5000];
int ret;
FILE *f;
size_t ilen;
size_t ilen, pem_len, buf_index;
memset( buf, 0, sizeof( buf ) );
memset( check_buf, 0, sizeof( check_buf ) );
@ -60,6 +68,14 @@ void pk_write_key_check( char * key_file )
ret = mbedtls_pk_write_key_pem( &key, buf, sizeof( buf ));
TEST_ASSERT( ret == 0 );
pem_len = strlen( (char *) buf );
// check that the rest of the buffer remains clear
for( buf_index = pem_len; buf_index < sizeof( buf ); ++buf_index )
{
TEST_ASSERT( buf[buf_index] == 0 );
}
f = fopen( key_file, "r" );
TEST_ASSERT( f != NULL );
ilen = fread( check_buf, 1, sizeof( check_buf ), f );

15
tests/suites/test_suite_x509write.function
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@ -45,7 +45,7 @@ void x509_csr_check( char * key_file, char * cert_req_check_file, int md_type,
unsigned char buf[4096];
unsigned char check_buf[4000];
int ret;
size_t olen = 0, pem_len = 0;
size_t olen = 0, pem_len = 0, buf_index;
int der_len = -1;
FILE *f;
const char *subject_name = "C=NL,O=PolarSSL,CN=PolarSSL Server 1";
@ -71,6 +71,11 @@ void x509_csr_check( char * key_file, char * cert_req_check_file, int md_type,
pem_len = strlen( (char *) buf );
for( buf_index = pem_len; buf_index < sizeof( buf ); ++buf_index )
{
TEST_ASSERT( buf[buf_index] == 0 );
}
f = fopen( cert_req_check_file, "r" );
TEST_ASSERT( f != NULL );
olen = fread( check_buf, 1, sizeof( check_buf ), f );
@ -113,7 +118,7 @@ void x509_crt_check( char *subject_key_file, char *subject_pwd,
unsigned char check_buf[5000];
mbedtls_mpi serial;
int ret;
size_t olen = 0, pem_len = 0;
size_t olen = 0, pem_len = 0, buf_index = 0;
int der_len = -1;
FILE *f;
rnd_pseudo_info rnd_info;
@ -182,6 +187,12 @@ void x509_crt_check( char *subject_key_file, char *subject_pwd,
pem_len = strlen( (char *) buf );
// check that the rest of the buffer remains clear
for( buf_index = pem_len; buf_index < sizeof( buf ); ++buf_index )
{
TEST_ASSERT( buf[buf_index] == 0 );
}
f = fopen( cert_check_file, "r" );
TEST_ASSERT( f != NULL );
olen = fread( check_buf, 1, sizeof( check_buf ), f );