* [PATCH v2 1/2] configfs: move CONFIGFS_MAGIC definition to magic.h
2026-08-19 23:45 [PATCH v2 0/2] ima: don't measure/appraise files on configfs Frederick Lawler
@ 2026-08-19 23:45 ` Frederick Lawler
2026-08-19 23:45 ` [PATCH v2 2/2] ima: don't measure/appraise files on configfs Frederick Lawler
1 sibling, 0 replies; 3+ messages in thread
From: Frederick Lawler @ 2026-08-19 23:45 UTC (permalink / raw)
To: Andreas Hindborg, Breno Leitao, Mimi Zohar, Roberto Sassu,
Dmitry Kasatkin, Eric Snowberg, Paul Moore, James Morris,
Serge E. Hallyn
Cc: linux-kernel, linux-integrity, linux-security-module, kernel-team,
Frederick Lawler
IMA shouldn't measure or appraise configfs, but currently does because
it's missing from the default exclusion policies. Move CONFIGFS_MAGIC to
magic.h to expose the file system's magic to IMA, as well as other userland
applications.
Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Frederick Lawler <fred@cloudflare.com>
---
fs/configfs/mount.c | 4 +---
include/uapi/linux/magic.h | 1 +
2 files changed, 2 insertions(+), 3 deletions(-)
diff --git a/fs/configfs/mount.c b/fs/configfs/mount.c
index 4929f343118946eaa55a539db4192e9c6621a8dc..d8cac1cbf3bd573a0549f2f044714c9d669205a4 100644
--- a/fs/configfs/mount.c
+++ b/fs/configfs/mount.c
@@ -9,6 +9,7 @@
*/
#include <linux/fs.h>
+#include <linux/magic.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/fs_context.h>
@@ -19,9 +20,6 @@
#include <linux/configfs.h>
#include "configfs_internal.h"
-/* Random magic number */
-#define CONFIGFS_MAGIC 0x62656570
-
static struct vfsmount *configfs_mount = NULL;
struct kmem_cache *configfs_dir_cachep;
static int configfs_mnt_count = 0;
diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
index 4f2da935a76ccae6e1c3310b2fae5379186548b8..d5b9958ddfaae90b270b66fe7853c5a3d49ce739 100644
--- a/include/uapi/linux/magic.h
+++ b/include/uapi/linux/magic.h
@@ -8,6 +8,7 @@
#define AUTOFS_SUPER_MAGIC 0x0187
#define CEPH_SUPER_MAGIC 0x00c36400
#define CODA_SUPER_MAGIC 0x73757245
+#define CONFIGFS_MAGIC 0x62656570 /* some random number */
#define CRAMFS_MAGIC 0x28cd3d45 /* some random number */
#define CRAMFS_MAGIC_WEND 0x453dcd28 /* magic number with the wrong endianess */
#define DEBUGFS_MAGIC 0x64626720
--
2.43.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* [PATCH v2 2/2] ima: don't measure/appraise files on configfs
2026-08-19 23:45 [PATCH v2 0/2] ima: don't measure/appraise files on configfs Frederick Lawler
2026-08-19 23:45 ` [PATCH v2 1/2] configfs: move CONFIGFS_MAGIC definition to magic.h Frederick Lawler
@ 2026-08-19 23:45 ` Frederick Lawler
1 sibling, 0 replies; 3+ messages in thread
From: Frederick Lawler @ 2026-08-19 23:45 UTC (permalink / raw)
To: Andreas Hindborg, Breno Leitao, Mimi Zohar, Roberto Sassu,
Dmitry Kasatkin, Eric Snowberg, Paul Moore, James Morris,
Serge E. Hallyn
Cc: linux-kernel, linux-integrity, linux-security-module, kernel-team,
Frederick Lawler, syzbot+448c2e24b1ceff13ed2a
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.
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>
---
Documentation/ABI/testing/ima_policy | 3 +++
security/integrity/ima/ima_policy.c | 7 ++++++-
2 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy
index 19258471b7b26b2c42c1ab2d11b4fd630b2e6f81..b8a763e4c9fb1a5ccca97518e80e0452554c9e96 100644
--- a/Documentation/ABI/testing/ima_policy
+++ b/Documentation/ABI/testing/ima_policy
@@ -108,6 +108,9 @@ Description:
# NSFS_MAGIC
dont_measure fsmagic=0x6e736673
dont_appraise fsmagic=0x6e736673
+ # CONFIGFS_MAGIC
+ dont_measure fsmagic=0x62656570
+ dont_appraise fsmagic=0x62656570
measure func=BPRM_CHECK
measure func=FILE_MMAP mask=MAY_EXEC
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},
--
2.43.0
^ permalink raw reply related [flat|nested] 3+ messages in thread