[PATCH v3] ima: process_measurement() needlessly takes inode_lock() on MAY_READ

[Roberto Sassu]

On Thu, 2025-03-27 at 11:09 -0500, Frederick Lawler wrote:
> On IMA policy update, if a measure rule exists in the policy,
> IMA_MEASURE is set for ima_policy_flags which makes the violation_check
> variable always true. Coupled with a no-action on MAY_READ for a
> FILE_CHECK call, we're always taking the inode_lock().
> 
> This becomes a performance problem for extremely heavy read-only workloads.
> Therefore, prevent this only in the case there's no action to be taken.
> 
> Signed-off-by: Frederick Lawler <fred at cloudflare.com>

Thanks Frederick!

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

Roberto

> ---
> Changes since v2:
> - s/mask & MAY_WRITE/file->f_mode & FMODE_WRITE/
> 
> Changes since v1:
> - Add MAY_WRITE && action check to violation_check to avoid MAY_READ
>   only situations
> ---
>  security/integrity/ima/ima_main.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index 9b87556b03a7..bc453f5a7531 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -237,7 +237,9 @@ static int process_measurement(struct file *file, const struct cred *cred,
>  				&allowed_algos);
>  	violation_check = ((func == FILE_CHECK || func == MMAP_CHECK ||
>  			    func == MMAP_CHECK_REQPROT) &&
> -			   (ima_policy_flag & IMA_MEASURE));
> +			   (ima_policy_flag & IMA_MEASURE) &&
> +			   ((action & IMA_MEASURE) ||
> +			    (file->f_mode & FMODE_WRITE)));
>  	if (!action && !violation_check)
>  		return 0;
>