[PATCH v2 v2] evm: check return values of crypto_shash functions

[Roberto Sassu]

On Thu, 2026-02-05 at 21:42 -0500, Daniel Hodges wrote:
> The crypto_shash_update() and crypto_shash_final() functions can fail
> and return error codes, but their return values were not being checked
> in several places in security/integrity/evm/evm_crypto.c:
> 
> - hmac_add_misc() ignored returns from crypto_shash_update() and
>   crypto_shash_final()
> - evm_calc_hmac_or_hash() ignored returns from crypto_shash_update()
> - evm_init_hmac() ignored returns from crypto_shash_update()
> 
> If these hash operations fail silently, the resulting HMAC could be
> invalid or incomplete, which could weaken the integrity verification
> security that EVM provides.
> 
> This patch converts hmac_add_misc() from void to int return type and
> adds proper error checking and propagation for all crypto_shash_*
> function calls. All callers are updated to handle the new return values.
> Additionally, error messages are logged when cryptographic operations
> fail to provide visibility into the failure rather than silently
> returning error codes.
> 
> Fixes: 66dbc325afce ("evm: re-release")
> Signed-off-by: Daniel Hodges <git at danielhodges.dev>

After fixing the minor issue below:

Reviewed-by: Roberto Sassu <roberto.sassu at huawei.com>

> ---
>  security/integrity/evm/evm_crypto.c | 55 ++++++++++++++++++++++-------
>  1 file changed, 42 insertions(+), 13 deletions(-)
> 
> diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
> index a5e730ffda57..402eb1ca64ce 100644
> --- a/security/integrity/evm/evm_crypto.c
> +++ b/security/integrity/evm/evm_crypto.c
> @@ -139,7 +139,7 @@ static struct shash_desc *init_desc(char type, uint8_t hash_algo)
>   * (Additional directory/file metadata needs to be added for more complete
>   * protection.)
>   */
> -static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
> +static int hmac_add_misc(struct shash_desc *desc, struct inode *inode,
>  			  char type, char *digest)
>  {
>  	struct h_misc {
> @@ -149,6 +149,7 @@ static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
>  		gid_t gid;
>  		umode_t mode;
>  	} hmac_misc;
> +	int error;
>  
>  	memset(&hmac_misc, 0, sizeof(hmac_misc));
>  	/* Don't include the inode or generation number in portable
> @@ -169,14 +170,28 @@ static void hmac_add_misc(struct shash_desc *desc, struct inode *inode,
>  	hmac_misc.uid = from_kuid(&init_user_ns, inode->i_uid);
>  	hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);
>  	hmac_misc.mode = inode->i_mode;
> -	crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
> +	error = crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof(hmac_misc));
> +	if (error) {
> +		pr_err("crypto_shash_update() failed: %d\n", error);
> +		return error;
> +	}
>  	if ((evm_hmac_attrs & EVM_ATTR_FSUUID) &&
> -	    type != EVM_XATTR_PORTABLE_DIGSIG)
> -		crypto_shash_update(desc, (u8 *)&inode->i_sb->s_uuid, UUID_SIZE);
> -	crypto_shash_final(desc, digest);
> +	    type != EVM_XATTR_PORTABLE_DIGSIG) {
> +		error = crypto_shash_update(desc, (u8 *)&inode->i_sb->s_uuid, UUID_SIZE);
> +		if (error) {
> +			pr_err("crypto_shash_update() failed: %d\n", error);
> +			return error;
> +		}
> +	}
> +	error = crypto_shash_final(desc, digest);
> +	if (error) {
> +		pr_err("crypto_shash_final() failed: %d\n", error);
> +		return error;
> +	}
>  
>  	pr_debug("hmac_misc: (%zu) [%*phN]\n", sizeof(struct h_misc),
>  		 (int)sizeof(struct h_misc), &hmac_misc);
> +	return 0;
>  }
>  
>  /*
> @@ -260,9 +275,12 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry,
>  
>  		if ((req_xattr_name && req_xattr_value)
>  		    && !strcmp(xattr->name, req_xattr_name)) {
> -			error = 0;
> -			crypto_shash_update(desc, (const u8 *)req_xattr_value,
> +			error = crypto_shash_update(desc, (const u8 *)req_xattr_value,
>  					     req_xattr_value_len);

Please align this.

Thanks

Roberto

> +			if (error) {
> +				pr_err("crypto_shash_update() failed: %d\n", error);
> +				goto out;
> +			}
>  			if (is_ima)
>  				ima_present = true;
>  
> @@ -286,15 +304,20 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry,
>  			pr_debug("file %s: xattr %s size mismatch (kernel: %d, user: %d)\n",
>  				 dentry->d_name.name, xattr->name, size,
>  				 user_space_size);
> -		error = 0;
>  		xattr_size = size;
> -		crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
> +		error = crypto_shash_update(desc, (const u8 *)xattr_value, xattr_size);
> +		if (error) {
> +			pr_err("crypto_shash_update() failed: %d\n", error);
> +			goto out;
> +		}
>  		if (is_ima)
>  			ima_present = true;
>  
>  		dump_security_xattr(xattr->name, xattr_value, xattr_size);
>  	}
> -	hmac_add_misc(desc, inode, type, data->digest);
> +	error = hmac_add_misc(desc, inode, type, data->digest);
> +	if (error)
> +		goto out;
>  
>  	if (inode != d_backing_inode(dentry) && iint) {
>  		if (IS_I_VERSION(inode))
> @@ -401,6 +424,7 @@ int evm_init_hmac(struct inode *inode, const struct xattr *xattrs,
>  {
>  	struct shash_desc *desc;
>  	const struct xattr *xattr;
> +	int error;
>  
>  	desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
>  	if (IS_ERR(desc)) {
> @@ -412,12 +436,17 @@ int evm_init_hmac(struct inode *inode, const struct xattr *xattrs,
>  		if (!evm_protected_xattr(xattr->name))
>  			continue;
>  
> -		crypto_shash_update(desc, xattr->value, xattr->value_len);
> +		error = crypto_shash_update(desc, xattr->value, xattr->value_len);
> +		if (error) {
> +			pr_err("crypto_shash_update() failed: %d\n", error);
> +			goto out;
> +		}
>  	}
>  
> -	hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
> +	error = hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
> +out:
>  	kfree(desc);
> -	return 0;
> +	return error;
>  }
>  
>  /*