Re: [PATCH 2/2] ima: don't measure/appraise files on configfs

[Mimi Zohar <zohar@linux.ibm.com>]

On Tue, 2026-08-18 at 14:35 -0500, Frederick Lawler wrote:
> When IMA appraises/measures a file configfs, it has an opportunity to
> hold onto the ima_iint_mutex while another file from a different file
> system is attempting to appraise/measure. This may cause a cyclical
> lock dependency.

The locking description is off a bit.

Suggested patch desciption from AI:

IMA measurement of a configfs file causes process_measurement() to hold iint-
>mutex while performing a kernel_read() to hash it, which re-enters configfs's
own file locking (buffer->mutex, frag_sem).

Separately, opening any file with O_TRUNC now causes ima_file_truncate() to take
iint->mutex to reset the cached action flags, while sb_writers is already held
for that mount.

When a configfs-backed nvmet namespace is involved, these two independent lock
chains combine into a cycle:

iint->mutex -> configfs locks -> subsys->lock -> sb_writers -> iint->mutex

Add configfs to the builtin don't measure/appraise rules, similarly to other
pseudo file systems, so IMA never takes iint->mutex for configfs file in the
first place.

> 
> Add configfs to the default don't measure/appraise lists, similarly to
> other pseudo file systems.
> 
> Reported-by: syzbot+448c2e24b1ceff13ed2a@syzkaller.appspotmail.com
> Link: https://lore.kernel.org/all/6a77c7cd.b50370da.49fe0.0031.GAE@google.com/
> Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
> Signed-off-by: Frederick Lawler <fred@cloudflare.com>

Sashiko is now enabled for the linux-integrity mailing list -
https://sashiko.dev/#/?list=org.kernel.vger.linux-integrity.   Please address
Sashiko's 2/2 review.

thanks,

Mimi

> ---
>  security/integrity/ima/ima_policy.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
> index f79d07bb63c6fc4ba6fe594140de8d59f57e4f0b..68d9a5e6c232ea0678e9f51f105cebecccccb43e 100644
> --- a/security/integrity/ima/ima_policy.c
> +++ b/security/integrity/ima/ima_policy.c
> @@ -165,7 +165,10 @@ static struct ima_rule_entry dont_measure_rules[] __ro_after_init = {
>  	{.action = DONT_MEASURE, .fsmagic = CGROUP2_SUPER_MAGIC,
>  	 .flags = IMA_FSMAGIC},
>  	{.action = DONT_MEASURE, .fsmagic = NSFS_MAGIC, .flags = IMA_FSMAGIC},
> -	{.action = DONT_MEASURE, .fsmagic = EFIVARFS_MAGIC, .flags = IMA_FSMAGIC}
> +	{.action = DONT_MEASURE, .fsmagic = EFIVARFS_MAGIC,
> +	 .flags = IMA_FSMAGIC},
> +	{.action = DONT_MEASURE, .fsmagic = CONFIGFS_MAGIC,
> +	 .flags = IMA_FSMAGIC}
>  };
>  
>  static struct ima_rule_entry original_measurement_rules[] __ro_after_init = {
> @@ -211,6 +214,8 @@ static struct ima_rule_entry default_appraise_rules[] __ro_after_init = {
>  	{.action = DONT_APPRAISE, .fsmagic = EFIVARFS_MAGIC, .flags = IMA_FSMAGIC},
>  	{.action = DONT_APPRAISE, .fsmagic = CGROUP_SUPER_MAGIC, .flags = IMA_FSMAGIC},
>  	{.action = DONT_APPRAISE, .fsmagic = CGROUP2_SUPER_MAGIC, .flags = IMA_FSMAGIC},
> +	{.action = DONT_APPRAISE, .fsmagic = CONFIGFS_MAGIC,
> +	 .flags = IMA_FSMAGIC},
>  #ifdef CONFIG_IMA_WRITE_POLICY
>  	{.action = APPRAISE, .func = POLICY_CHECK,
>  	.flags = IMA_FUNC | IMA_DIGSIG_REQUIRED},