On Fri, 2026-01-30 at 16:39 -0600, Frederick Lawler wrote:
> IMA performs unnecessary measurements on files in stacked file systems
> that do not set kstat.change_cookie to an inode's i_version.
>
> For example: TMPFS (upper) is stacked onto XFS (lower).
> Actions files result in re-measurement because commit 1cf7e834a6fb
> ("xfs: switch to multigrain timestamps") introduced multigrain
> timestamps into XFS which changed the kstat.change_cookie semantics
> to no longer supply an i_version to compare against in
> integrity_inode_attributes_changed(). Once the inode is in TMPFS,
> the change detection behavior operates as normal because TMPFS updates
> kstat.change_cookie to the i_version.
>
> Instead, fall back onto a ctime comparison. This also gives file systems
> that do not support i_version an opportunity avoid the same behavior,
> as they're more likely to have ctime support.
>
> timespec64_to_ns() is chosen to avoid adding extra storage to
> integrity_inode_attributes by leveraging the existing version field.
Correct me if I'm wrong, but this issue seems to me xfs-specific. In
that case, maybe it is better to remove the stacked filesystem part,
which might be misleading.
Thanks
Roberto
> Link: https://lore.kernel.org/all/aTspr4_h9IU4EyrR@CMGLRV3
> Fixes: 1cf7e834a6fb ("xfs: switch to multigrain timestamps")
> Suggested-by: Jeff Layton <[email protected]>
> Signed-off-by: Frederick Lawler <[email protected]>
> ---
> include/linux/integrity.h | 6 +++++-
> security/integrity/ima/ima_api.c | 11 ++++++++---
> security/integrity/ima/ima_main.c | 2 +-
> 3 files changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/integrity.h b/include/linux/integrity.h
> index
> 382c783f0fa3ae4a938cdf9559291ba1903a378e..ec2c94907f417c4a71ecce29ac79edac9bc2c6f8
> 100644
> --- a/include/linux/integrity.h
> +++ b/include/linux/integrity.h
> @@ -10,6 +10,7 @@
> #include <linux/fs.h>
> #include <linux/iversion.h>
> #include <linux/kernel.h>
> +#include <linux/time64.h>
>
> enum integrity_status {
> INTEGRITY_PASS = 0,
> @@ -58,6 +59,9 @@ integrity_inode_attrs_stat_changed
> if (stat->result_mask & STATX_CHANGE_COOKIE)
> return stat->change_cookie != attrs->version;
>
> + if (stat->result_mask & STATX_CTIME)
> + return timespec64_to_ns(&stat->ctime) != (s64)attrs->version;
> +
> return true;
> }
>
> @@ -84,7 +88,7 @@ integrity_inode_attrs_changed(const struct
> integrity_inode_attributes *attrs,
> * only for IMA if vfs_getattr_nosec() fails.
> */
> if (!file || vfs_getattr_nosec(&file->f_path, &stat,
> - STATX_CHANGE_COOKIE,
> + STATX_CHANGE_COOKIE | STATX_CTIME,
> AT_STATX_SYNC_AS_STAT))
> return !IS_I_VERSION(inode) ||
> !inode_eq_iversion(inode, attrs->version);
> diff --git a/security/integrity/ima/ima_api.c
> b/security/integrity/ima/ima_api.c
> index
> c35ea613c9f8d404ba4886e3b736c3bab29d1668..e47d6281febc15a0ac1bd2ea1d28fea4d0cd5c58
> 100644
> --- a/security/integrity/ima/ima_api.c
> +++ b/security/integrity/ima/ima_api.c
> @@ -272,10 +272,15 @@ int ima_collect_measurement(struct ima_iint_cache
> *iint, struct file *file,
> * to an initial measurement/appraisal/audit, but was modified to
> * assume the file changed.
> */
> - result = vfs_getattr_nosec(&file->f_path, &stat, STATX_CHANGE_COOKIE,
> + result = vfs_getattr_nosec(&file->f_path, &stat,
> + STATX_CHANGE_COOKIE | STATX_CTIME,
> AT_STATX_SYNC_AS_STAT);
> - if (!result && (stat.result_mask & STATX_CHANGE_COOKIE))
> - i_version = stat.change_cookie;
> + if (!result) {
> + if (stat.result_mask & STATX_CHANGE_COOKIE)
> + i_version = stat.change_cookie;
> + else if (stat.result_mask & STATX_CTIME)
> + i_version = timespec64_to_ns(&stat.ctime);
> + }
> hash.hdr.algo = algo;
> hash.hdr.length = hash_digest_size[algo];
>
> diff --git a/security/integrity/ima/ima_main.c
> b/security/integrity/ima/ima_main.c
> index
> 8cb17c9d446caaa5a98f5ec8f027c17ba7babca8..776db158b0bd8a0d053729ac0cc15af8b6020a98
> 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -199,7 +199,7 @@ static void ima_check_last_writer(struct ima_iint_cache
> *iint,
> &iint->atomic_flags);
> if ((iint->flags & IMA_NEW_FILE) ||
> vfs_getattr_nosec(&file->f_path, &stat,
> - STATX_CHANGE_COOKIE,
> + STATX_CHANGE_COOKIE | STATX_CTIME,
> AT_STATX_SYNC_AS_STAT) ||
> integrity_inode_attrs_stat_changed(&iint->real_inode,
> &stat)) {
>
