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Call setbuf when reading or writing files: library

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After opening a file containing sensitive data, call mbedtls_setbuf() to
disable buffering. This way, we don't expose sensitive data to a memory
disclosure vulnerability in a buffer outside our control.

This commit adds a call to mbedtls_setbuf() after each call to fopen(),
except:
* In ctr_drbg.c, in load_file(), because this is only used for DH parameters
  and they are not confidential data.
* In psa_its_file.c, in psa_its_remove(), because the file is only opened
  to check its existence, we don't read data from it.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine
2022-06-30 17:03:40 +02:00
parent 6497b5a1d1
commit da0913ba6b
8 changed files with 36 additions and 1 deletions
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6
library/entropy.c
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@@ -457,6 +457,9 @@ int mbedtls_entropy_write_seed_file( mbedtls_entropy_context *ctx, const char *p
goto exit;
}
/* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
mbedtls_setbuf( f, NULL );
if( fwrite( buf, 1, MBEDTLS_ENTROPY_BLOCK_SIZE, f ) != MBEDTLS_ENTROPY_BLOCK_SIZE )
{
ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
@@ -484,6 +487,9 @@ int mbedtls_entropy_update_seed_file( mbedtls_entropy_context *ctx, const char *
if( ( f = fopen( path, "rb" ) ) == NULL )
return( MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR );
/* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
mbedtls_setbuf( f, NULL );
fseek( f, 0, SEEK_END );
n = (size_t) ftell( f );
fseek( f, 0, SEEK_SET );