Simplify mbedtls_debug_print_mpi and fix the case of empty bignums
Rewrite mbedtls_debug_print_mpi to be simpler and smaller. Leverage
mbedtls_mpi_bitlen() instead of manually looking for the leading
zeros.
Fix #4608: the old code made an invalid memory dereference when
X->n==0 (freshly initialized bignum with the value 0).
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/debug.c b/library/debug.c
index 4be2cba..e520258 100644
--- a/library/debug.c
+++ b/library/debug.c
@@ -220,8 +220,8 @@
const char *text, const mbedtls_mpi *X )
{
char str[DEBUG_BUF_SIZE];
- int j, k, zeros = 1;
- size_t i, n, idx = 0;
+ size_t bitlen;
+ size_t idx = 0;
if( NULL == ssl ||
NULL == ssl->conf ||
@@ -232,55 +232,43 @@
return;
}
- for( n = X->n - 1; n > 0; n-- )
- if( X->p[n] != 0 )
- break;
+ bitlen = mbedtls_mpi_bitlen( X );
- for( j = ( sizeof(mbedtls_mpi_uint) << 3 ) - 1; j >= 0; j-- )
- if( ( ( X->p[n] >> j ) & 1 ) != 0 )
- break;
-
- mbedtls_snprintf( str + idx, sizeof( str ) - idx, "value of '%s' (%d bits) is:\n",
- text, (int) ( ( n * ( sizeof(mbedtls_mpi_uint) << 3 ) ) + j + 1 ) );
-
+ mbedtls_snprintf( str, sizeof( str ), "value of '%s' (%u bits) is:\n",
+ text, (unsigned) bitlen );
debug_send_line( ssl, level, file, line, str );
- idx = 0;
- for( i = n + 1, j = 0; i > 0; i-- )
+ if( bitlen == 0 )
{
- if( zeros && X->p[i - 1] == 0 )
- continue;
-
- for( k = sizeof( mbedtls_mpi_uint ) - 1; k >= 0; k-- )
+ str[0] = ' '; str[1] = '0'; str[2] = '0';
+ idx = 3;
+ }
+ else
+ {
+ int n;
+ for( n = ( bitlen - 1 ) / 8; n >= 0; n-- )
{
- if( zeros && ( ( X->p[i - 1] >> ( k << 3 ) ) & 0xFF ) == 0 )
- continue;
- else
- zeros = 0;
-
- if( j % 16 == 0 )
+ size_t limb_offset = n / sizeof( mbedtls_mpi_uint );
+ size_t offset_in_limb = n % sizeof( mbedtls_mpi_uint );
+ unsigned char octet =
+ ( X->p[limb_offset] >> ( offset_in_limb * 8 ) ) & 0xff;
+ mbedtls_snprintf( str + idx, sizeof( str ) - idx, " %02x", octet );
+ idx += 3;
+ /* Wrap lines after 16 octets that each take 3 columns */
+ if( idx >= 3 * 16 )
{
- if( j > 0 )
- {
- mbedtls_snprintf( str + idx, sizeof( str ) - idx, "\n" );
- debug_send_line( ssl, level, file, line, str );
- idx = 0;
- }
+ mbedtls_snprintf( str + idx, sizeof( str ) - idx, "\n" );
+ debug_send_line( ssl, level, file, line, str );
+ idx = 0;
}
-
- idx += mbedtls_snprintf( str + idx, sizeof( str ) - idx, " %02x", (unsigned int)
- ( X->p[i - 1] >> ( k << 3 ) ) & 0xFF );
-
- j++;
}
-
}
- if( zeros == 1 )
- idx += mbedtls_snprintf( str + idx, sizeof( str ) - idx, " 00" );
-
- mbedtls_snprintf( str + idx, sizeof( str ) - idx, "\n" );
- debug_send_line( ssl, level, file, line, str );
+ if( idx != 0 )
+ {
+ mbedtls_snprintf( str + idx, sizeof( str ) - idx, "\n" );
+ debug_send_line( ssl, level, file, line, str );
+ }
}
#endif /* MBEDTLS_BIGNUM_C */