pk.c: Ensure min hash_len in pk_hashlen_helper
The function `pk_hashlen_helper` exists to ensure a valid hash_len is
used in pk_verify and pk_sign functions. This function has been
used to adjust to the corrsponding hash_len if the user passes in 0
for the hash_len argument based on the md algorithm given. If the user
does not pass in 0 as the hash_len, then it is not adjusted. This is
problematic if the user gives a hash_len and hash buffer that is less than the
associated length of the md algorithm. This error would go unchecked
and eventually lead to buffer overread when given to specific pk_sign/verify
functions, since they both ignore the hash_len argument if md_alg is not
MBEDTLS_MD_NONE.
This commit, adds a conditional to `pk_hashlen_helper` so that an
error is thrown if the user specifies a hash_length (not 0) and it is
less than the expected for the associated message digest algorithm.
This aligns better with the api documentation where it states "If
hash_len is 0, then the length associated with md_alg is used instead,
or an error returned if it is invalid"
Signed-off-by: Nick Child <nick.child@ibm.com>
Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
diff --git a/ChangeLog.d/ensure_hash_len_is_valid.txt b/ChangeLog.d/ensure_hash_len_is_valid.txt
new file mode 100644
index 0000000..2059249
--- /dev/null
+++ b/ChangeLog.d/ensure_hash_len_is_valid.txt
@@ -0,0 +1,5 @@
+Bugfix
+ * mbedtls_pk_sign() and mbedtls_pk_verify() and their extended and
+ restartable variants now require at least the specified hash length if
+ nonzero. Before, for RSA, hash_len was ignored in favor of the length of
+ the specified hash algorithm.
diff --git a/library/pk.c b/library/pk.c
index 81cfdbf..8998271 100644
--- a/library/pk.c
+++ b/library/pk.c
@@ -225,12 +225,15 @@
{
const mbedtls_md_info_t *md_info;
- if( *hash_len != 0 )
+ if( *hash_len != 0 && md_alg == MBEDTLS_MD_NONE )
return( 0 );
if( ( md_info = mbedtls_md_info_from_type( md_alg ) ) == NULL )
return( -1 );
+ if ( *hash_len != 0 && *hash_len < mbedtls_md_get_size( md_info ) )
+ return ( -1 );
+
*hash_len = mbedtls_md_get_size( md_info );
return( 0 );
}