Call setbuf when reading or writing files: library
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>
diff --git a/library/md.c b/library/md.c
index f2c1a90..a387da5 100644
--- a/library/md.c
+++ b/library/md.c
@@ -605,6 +605,9 @@
if( ( f = fopen( path, "rb" ) ) == NULL )
return( MBEDTLS_ERR_MD_FILE_IO_ERROR );
+ /* Ensure no stdio buffering of secrets, as such buffers cannot be wiped. */
+ mbedtls_setbuf( f, NULL );
+
mbedtls_md_init( &ctx );
if( ( ret = mbedtls_md_setup( &ctx, md_info, 0 ) ) != 0 )