[PATCH 1/1] IMA event log trimming

[Roberto Sassu]

On Tue, 2025-12-02 at 15:28 -0800, steven chen wrote:
> This patch is for trimming N entries of the IMA event logs as well as
> cleaning the hash table.
> 
> It provides a userspace interface ima_trim_log that can be used to input
> number N to let kernel to trim N entries of IMA event logs. When read
> this interface, it returns number of entries trimmed last tim.

High-level comments:
- It does not offer the possibility to keep the hash table
- There is no coordination between taking a snapshot and the readers of
  the measurements list (I think it is necessary, since reading is
  based on *pos, which contains the entries read until a given point;
  if there is a truncate in the middle of the read, *pos would still
  refer to the non-truncated list and the next read will skip some
  measurement entries)
- While trimming per se is ok, I like more the idea of staging changes
  and letting the user delete the staged measurements list later

> A mutex ima_trim_list_mutex is provided to allow one trimming request
> at a time.
> 
> Signed-off-by: steven chen <chenste at linux.microsoft.com>
> ---
>  security/integrity/ima/ima.h       |  2 +
>  security/integrity/ima/ima_fs.c    | 78 ++++++++++++++++++++++++++++++
>  security/integrity/ima/ima_queue.c | 42 ++++++++++++++++
>  3 files changed, 122 insertions(+)
> 
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index e3d71d8d56e3..ab0e30ee25ea 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -246,8 +246,10 @@ void ima_post_key_create_or_update(struct key *keyring, struct key *key,
>  
>  #ifdef CONFIG_IMA_KEXEC
>  void ima_measure_kexec_event(const char *event_name);
> +long ima_purge_event_log(long number_logs);
>  #else
>  static inline void ima_measure_kexec_event(const char *event_name) {}
> +static inline long ima_purge_event_log(long number_logs) { return 0; }
>  #endif
>  
>  /*
> diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> index 87045b09f120..ea93448feedd 100644
> --- a/security/integrity/ima/ima_fs.c
> +++ b/security/integrity/ima/ima_fs.c
> @@ -38,6 +38,11 @@ __setup("ima_canonical_fmt", default_canonical_fmt_setup);
>  
>  static int valid_policy = 1;
>  
> +#define IMA_LOG_TRIM_REQ_LENGTH 11
> +static long trimcount;
> +/* mutex protects atomicity of trimming measurement list requests */
> +static DEFINE_MUTEX(ima_trim_list_mutex);
> +
>  static ssize_t ima_show_htable_value(char __user *buf, size_t count,
>  				     loff_t *ppos, atomic_long_t *val)
>  {
> @@ -289,6 +294,69 @@ static const struct file_operations ima_ascii_measurements_ops = {
>  	.release = seq_release,
>  };
>  
> +static int ima_log_trim_open(struct inode *inode, struct file *filp)
> +{
> +	if (!capable(CAP_SYS_ADMIN))
> +		return -EPERM;
> +	return 0;
> +}
> +
> +static ssize_t ima_log_trim_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
> +{
> +	char tmpbuf[IMA_LOG_TRIM_REQ_LENGTH];	/* greater than largest 'long' string value */
> +	ssize_t len;
> +
> +	len = scnprintf(tmpbuf, sizeof(tmpbuf), "%li\n", trimcount);
> +	return simple_read_from_buffer(buf, size, ppos, tmpbuf, len);
> +}
> +
> +static ssize_t ima_log_trim_write(struct file *file,
> +				  const char __user *buf, size_t datalen, loff_t *ppos)
> +{
> +	unsigned char req[IMA_LOG_TRIM_REQ_LENGTH];
> +	long count, n;
> +	int ret;
> +
> +	mutex_lock(&ima_trim_list_mutex);
> +
> +	if (*ppos > 0 || datalen > IMA_LOG_TRIM_REQ_LENGTH || datalen < 2) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	n = (int)datalen;
> +
> +	ret = copy_from_user(req, buf, datalen);
> +	if (ret < 0)
> +		goto out;
> +
> +	count = 0;
> +	for (int i = 0; i < n; ++i) {
> +		if (req[i] < '0' || req[i] > '9') {
> +			ret = -EINVAL;
> +			goto out;
> +		}
> +		count = count * 10 + req[i] - '0';
> +	}
> +	ret = ima_purge_event_log(count);
> +
> +	if (ret < 0)
> +		goto out;
> +
> +	trimcount = ret;
> +	ret = datalen;
> +out:
> +	mutex_unlock(&ima_trim_list_mutex);
> +	return ret;
> +}
> +
> +static const struct file_operations ima_log_trim_ops = {
> +	.open = ima_log_trim_open,
> +	.read = ima_log_trim_read,
> +	.write = ima_log_trim_write,
> +	.llseek = generic_file_llseek,
> +};
> +
>  static ssize_t ima_read_policy(char *path)
>  {
>  	void *data = NULL;
> @@ -528,6 +596,16 @@ int __init ima_fs_init(void)
>  		goto out;
>  	}
>  
> +	dentry = securityfs_create_file("ima_trim_log",
> +					S_IRUSR | S_IRGRP | S_IWUSR | S_IWGRP,
> +					ima_dir, NULL, &ima_log_trim_ops);
> +	if (IS_ERR(dentry)) {
> +		ret = PTR_ERR(dentry);
> +		goto out;
> +	}
> +
> +	trimcount = 0;
> +
>  	dentry = securityfs_create_file("runtime_measurements_count",
>  				   S_IRUSR | S_IRGRP, ima_dir, NULL,
>  				   &ima_measurements_count_ops);
> diff --git a/security/integrity/ima/ima_queue.c b/security/integrity/ima/ima_queue.c
> index 590637e81ad1..999cd42c517c 100644
> --- a/security/integrity/ima/ima_queue.c
> +++ b/security/integrity/ima/ima_queue.c
> @@ -220,6 +220,48 @@ int ima_add_template_entry(struct ima_template_entry *entry, int violation,
>  	return result;
>  }
>  
> +/* Delete the IMA event logs */
> +long ima_purge_event_log(long number_logs)
> +{
> +	struct ima_queue_entry *qe;
> +	long cur = 0;
> +
> +	if (number_logs <= 0)
> +		return number_logs;
> +
> +	mutex_lock(&ima_extend_list_mutex);
> +	rcu_read_lock();

Sorry, I'm missing why rcu_read_lock() is needed.

> +
> +	/*
> +	 * Remove this entry from both hash table and the measurement list
> +	 * When removing from hash table, decrease the length counter
> +	 * so that the hash table re-sizing logic works correctly
> +	 */
> +	list_for_each_entry_rcu(qe, &ima_measurements, later) {
> +		int i;
> +
> +		/* if CONFIG_IMA_DISABLE_HTABLE is set, the hash table is not used */
> +		if (!IS_ENABLED(CONFIG_IMA_DISABLE_HTABLE))
> +			hlist_del_rcu(&qe->hnext);
> +
> +		for (i = 0; i < qe->entry->template_desc->num_fields; i++) {
> +			kfree(qe->entry->template_data[i].data);
> +			qe->entry->template_data[i].data = NULL;
> +			qe->entry->template_data[i].len = 0;
> +		}
> +
> +		atomic_long_dec(&ima_htable.len);
> +		list_del_rcu(&qe->later);

Missing kfree() of qe->entry and qe?

Thanks

Roberto

> +		++cur;
> +		if (cur >= number_logs)
> +			break;
> +	}
> +
> +	rcu_read_unlock();
> +	mutex_unlock(&ima_extend_list_mutex);
> +	return cur;
> +}
> +
>  int ima_restore_measurement_entry(struct ima_template_entry *entry)
>  {
>  	int result = 0;