Re: [PATCH v4 15/17] module: Introduce hash-based integrity checking

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2026-03-10 18:12:18 [-0700], Eric Biggers wrote:
> > diff --git a/scripts/modules-merkle-tree.c b/scripts/modules-merkle-tree.c
> [...]
> 
> > +struct file_entry {
> > +	char *name;
> > +	unsigned int pos;
> > +	unsigned char hash[EVP_MAX_MD_SIZE];
> 
> Considering that the hash algorithm is fixed, EVP_MAX_MD_SIZE can be
> replaced with a tighter local definition:
> 
>     #define MAX_HASH_SIZE 32
> 
> > +static struct file_entry *fh_list;
> > +static size_t num_files;
> > +
> > +struct leaf_hash {
> > +	unsigned char hash[EVP_MAX_MD_SIZE];
> > +};
> > +
> > +struct mtree {
> > +	struct leaf_hash **l;
> > +	unsigned int *entries;
> > +	unsigned int levels;
> > +};
> 
> 'struct leaf_hash' is confusing because it's actually used for the
> hashes of internal nodes, not leaf nodes.

You could still consider the internal nodes as leafs.

> Maybe rename it to 'struct hash' and use it for both the hashes and leaf
> nodes and internal nodes.
> 
> Also, clearer naming would improve readability, e.g.:
> 
>     struct merkle_tree {
>             struct hash **level_hashes;
>             unsigned int level_size;
>             unsigned int num_levels;
>     };

but this could improve it, indeed.

> > +	hash_evp = EVP_get_digestbyname("sha256");
> 
> EVP_sha256()

I would suggest to use EVP_MD_fetch() instead.

> > +	hash_size = EVP_MD_get_size(hash_evp);
> 
> The old name 'EVP_MD_size()' would have wider compatibility.

EVP_MD_fetch() and EVP_MD_get_size() are openssl 3.0.0+ and nothing
below 3.0.0 is considered supported (while 3.0.0 is EOL 07 Sep 2026).

Sebastian