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Add setbuf platform function

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Add a platform function mbedtls_setbuf(), defaulting to setbuf().

The intent is to allow disabling stdio buffering when reading or writing
files with sensitive data, because this exposes the sensitive data to a
subsequent memory disclosure vulnerability.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine
2022-06-30 17:01:40 +02:00
parent a745c7d439
commit 6497b5a1d1
5 changed files with 101 additions and 0 deletions
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28
library/platform.c
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@ -226,6 +226,28 @@ int mbedtls_platform_set_fprintf( int (*fprintf_func)( FILE *, const char *, ...
}
#endif /* MBEDTLS_PLATFORM_FPRINTF_ALT */
#if defined(MBEDTLS_PLATFORM_SETBUF_ALT)
#if !defined(MBEDTLS_PLATFORM_STD_SETBUF)
/*
* Make dummy function to prevent NULL pointer dereferences
*/
static void platform_setbuf_uninit( FILE *stream, char *buf )
{
(( void ) stream);
(( void ) buf);
}
#define MBEDTLS_PLATFORM_STD_SETBUF platform_setbuf_uninit
#endif /* !MBEDTLS_PLATFORM_STD_SETBUF */
void (*mbedtls_setbuf)( FILE *stream, char *buf ) = MBEDTLS_PLATFORM_STD_SETBUF;
int mbedtls_platform_set_setbuf( void (*setbuf_func)( FILE *stream, char *buf ) )
{
mbedtls_setbuf = setbuf_func;
return( 0 );
}
#endif /* MBEDTLS_PLATFORM_SETBUF_ALT */
#if defined(MBEDTLS_PLATFORM_EXIT_ALT)
#if !defined(MBEDTLS_PLATFORM_STD_EXIT)
/*
@ -288,6 +310,9 @@ int mbedtls_platform_std_nv_seed_read( unsigned char *buf, size_t buf_len )
if( ( file = fopen( MBEDTLS_PLATFORM_STD_NV_SEED_FILE, "rb" ) ) == NULL )
return( -1 );
/* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
mbedtls_setbuf( file, NULL );
if( ( n = fread( buf, 1, buf_len, file ) ) != buf_len )
{
fclose( file );
@ -307,6 +332,9 @@ int mbedtls_platform_std_nv_seed_write( unsigned char *buf, size_t buf_len )
if( ( file = fopen( MBEDTLS_PLATFORM_STD_NV_SEED_FILE, "w" ) ) == NULL )
return -1;
/* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
mbedtls_setbuf( file, NULL );
if( ( n = fwrite( buf, 1, buf_len, file ) ) != buf_len )
{
fclose( file );