From ee134670625514ff78c272d26059b2496d113137 Mon Sep 17 00:00:00 2001 From: Nick Child Date: Tue, 25 May 2021 15:31:21 -0400 Subject: [PATCH] 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 not eqaul to 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 Signed-off-by: Nayna Jain --- library/pk.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/library/pk.c b/library/pk.c index 06021e26c0aa..bb88fca531e3 100644 --- a/library/pk.c +++ b/library/pk.c @@ -235,12 +235,15 @@ static inline int pk_hashlen_helper( mbedtls_md_type_t md_alg, size_t *hash_len { 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 ); }