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Base64 decode: simplify local variables

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Document what each local variable does when it isn't obvious from the name.
Don't reuse a variable for different purposes.

This commit has very little impact on the generated code (same code size on
a sample Thumb build), although it does fix a theoretical bug that 2^32
spaces inside a line would be ignored instead of treated as an error.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-07-28 14:20:06 +02:00
parent c48ab11400
commit a97e911e5d
1 changed files with 21 additions and 21 deletions
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42
library/base64.c
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@ -240,19 +240,22 @@ static signed char dec_value( unsigned char c )
int mbedtls_base64_decode( unsigned char *dst, size_t dlen, size_t *olen, int mbedtls_base64_decode( unsigned char *dst, size_t dlen, size_t *olen,
const unsigned char *src, size_t slen ) const unsigned char *src, size_t slen )
{ {
size_t i, n; size_t i; /* index in source */
uint32_t j, x; size_t n; /* number of digits or trailing = in source */
uint32_t x; /* value accumulator */
unsigned equals = 0;
int spaces_present = 0;
unsigned char *p; unsigned char *p;
/* First pass: check for validity and get output length */ /* First pass: check for validity and get output length */
for( i = n = j = 0; i < slen; i++ ) for( i = n = 0; i < slen; i++ )
{ {
/* Skip spaces before checking for EOL */ /* Skip spaces before checking for EOL */
x = 0; spaces_present = 0;
while( i < slen && src[i] == ' ' ) while( i < slen && src[i] == ' ' )
{ {
++i; ++i;
++x; spaces_present = 1;
} }
/* Spaces at end of buffer are OK */ /* Spaces at end of buffer are OK */
@ -267,7 +270,7 @@ int mbedtls_base64_decode( unsigned char *dst, size_t dlen, size_t *olen,
continue; continue;
/* Space inside a line is an error */ /* Space inside a line is an error */
if( x != 0 ) if( spaces_present )
return( MBEDTLS_ERR_BASE64_INVALID_CHARACTER ); return( MBEDTLS_ERR_BASE64_INVALID_CHARACTER );
if( src[i] > 127 ) if( src[i] > 127 )
@ -275,12 +278,12 @@ int mbedtls_base64_decode( unsigned char *dst, size_t dlen, size_t *olen,
if( src[i] == '=' ) if( src[i] == '=' )
{ {
if( ++j > 2 ) if( ++equals > 2 )
return( MBEDTLS_ERR_BASE64_INVALID_CHARACTER ); return( MBEDTLS_ERR_BASE64_INVALID_CHARACTER );
} }
else else
{ {
if( j != 0 ) if( equals != 0 )
return( MBEDTLS_ERR_BASE64_INVALID_CHARACTER ); return( MBEDTLS_ERR_BASE64_INVALID_CHARACTER );
if( dec_value( src[i] ) < 0 ) if( dec_value( src[i] ) < 0 )
return( MBEDTLS_ERR_BASE64_INVALID_CHARACTER ); return( MBEDTLS_ERR_BASE64_INVALID_CHARACTER );
@ -299,7 +302,7 @@ int mbedtls_base64_decode( unsigned char *dst, size_t dlen, size_t *olen,
* n = ( ( n * 6 ) + 7 ) >> 3; * n = ( ( n * 6 ) + 7 ) >> 3;
*/ */
n = ( 6 * ( n >> 3 ) ) + ( ( 6 * ( n & 0x7 ) + 7 ) >> 3 ); n = ( 6 * ( n >> 3 ) ) + ( ( 6 * ( n & 0x7 ) + 7 ) >> 3 );
n -= j; n -= equals;
if( dst == NULL || dlen < n ) if( dst == NULL || dlen < n )
{ {
@ -307,27 +310,24 @@ int mbedtls_base64_decode( unsigned char *dst, size_t dlen, size_t *olen,
return( MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL ); return( MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL );
} }
for( j = 3, n = x = 0, p = dst; i > 0; i--, src++ ) equals = 0;
{ for( n = x = 0, p = dst; i > 0; i--, src++ )
{
if( *src == '\r' || *src == '\n' || *src == ' ' ) if( *src == '\r' || *src == '\n' || *src == ' ' )
continue; continue;
x = x << 6;
if( *src == '=' ) if( *src == '=' )
{ ++equals;
--j;
x = x << 6;
}
else else
{ x |= dec_value( *src );
x = ( x << 6 ) | ( dec_value( *src ) & 0x3F );
}
if( ++n == 4 ) if( ++n == 4 )
{ {
n = 0; n = 0;
if( j > 0 ) *p++ = MBEDTLS_BYTE_2( x ); *p++ = MBEDTLS_BYTE_2( x );
if( j > 1 ) *p++ = MBEDTLS_BYTE_1( x ); if( equals <= 1 ) *p++ = MBEDTLS_BYTE_1( x );
if( j > 2 ) *p++ = MBEDTLS_BYTE_0( x ); if( equals <= 0 ) *p++ = MBEDTLS_BYTE_0( x );
} }
} }