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Message-Id: <20240415161044.2572438-3-roberto.sassu@huaweicloud.com>
Date: Mon, 15 Apr 2024 18:10:37 +0200
From: Roberto Sassu <roberto.sassu@...weicloud.com>
To: corbet@....net,
zohar@...ux.ibm.com,
dmitry.kasatkin@...il.com,
eric.snowberg@...cle.com,
paul@...l-moore.com,
jmorris@...ei.org,
serge@...lyn.com
Cc: linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org,
linux-integrity@...r.kernel.org,
linux-security-module@...r.kernel.org,
wufan@...ux.microsoft.com,
pbrobinson@...il.com,
zbyszek@...waw.pl,
hch@....de,
mjg59@...f.ucam.org,
pmatilai@...hat.com,
jannh@...gle.com,
dhowells@...hat.com,
jikos@...nel.org,
mkoutny@...e.com,
ppavlu@...e.com,
petr.vorel@...il.com,
mzerqung@...inter.de,
kgold@...ux.ibm.com,
Roberto Sassu <roberto.sassu@...wei.com>
Subject: [RFC][PATCH v2 2/9] ima: Nest iint mutex for DIGEST_LIST_CHECK hook
From: Roberto Sassu <roberto.sassu@...wei.com>
Invoking digest_cache_get() inside the iint->mutex critical region can
cause deadlocks due to the fact that IMA can be recursively invoked for
reading the digest list. The deadlock would occur if the digest_cache LSM
attempts to read the same inode that is already locked by IMA.
However, since the digest_cache LSM makes sure that the above situation
never happens, as it checks the inodes, it is safe to call
digest_cache_get() inside the critical region and nest the iint->mutex
when the DIGEST_LIST_CHECK hook is executed.
Add a lockdep subclass to the iint->mutex, that is 0 if the IMA hook
executed is not DIGEST_LIST_CHECK, and 1 when it is. Since lockdep allows
nesting with higher classes and subclasses, that effectively eliminates the
warning about the unsafe lock.
Pass the new lockdep subclass (nested variable) from ima_inode_get() to
ima_iint_init_always() and ima_iint_lockdep_annotate().
Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
---
security/integrity/ima/ima.h | 2 +-
security/integrity/ima/ima_iint.c | 17 +++++++++++------
security/integrity/ima/ima_main.c | 6 +++---
3 files changed, 15 insertions(+), 10 deletions(-)
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index cea4517e73ab..c9140a57b591 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -216,7 +216,7 @@ static inline void ima_inode_set_iint(const struct inode *inode,
}
struct ima_iint_cache *ima_iint_find(struct inode *inode);
-struct ima_iint_cache *ima_inode_get(struct inode *inode);
+struct ima_iint_cache *ima_inode_get(struct inode *inode, bool nested);
void ima_inode_free(struct inode *inode);
void __init ima_iintcache_init(void);
diff --git a/security/integrity/ima/ima_iint.c b/security/integrity/ima/ima_iint.c
index e7c9c216c1c6..c98a30815c8a 100644
--- a/security/integrity/ima/ima_iint.c
+++ b/security/integrity/ima/ima_iint.c
@@ -39,9 +39,12 @@ struct ima_iint_cache *ima_iint_find(struct inode *inode)
* files both on overlayfs and on underlying fs, we need to annotate the iint
* mutex to avoid lockdep false positives related to IMA + overlayfs.
* See ovl_lockdep_annotate_inode_mutex_key() for more details.
+ *
+ * In addition to that, safely ignored nested locks for digest lists, since
+ * the digest_cache LSM prevents circular dependencies.
*/
static inline void ima_iint_lockdep_annotate(struct ima_iint_cache *iint,
- struct inode *inode)
+ struct inode *inode, bool nested)
{
#ifdef CONFIG_LOCKDEP
static struct lock_class_key ima_iint_mutex_key[IMA_MAX_NESTING];
@@ -51,12 +54,13 @@ static inline void ima_iint_lockdep_annotate(struct ima_iint_cache *iint,
if (WARN_ON_ONCE(depth < 0 || depth >= IMA_MAX_NESTING))
depth = 0;
- lockdep_set_class(&iint->mutex, &ima_iint_mutex_key[depth]);
+ lockdep_set_class_and_subclass(&iint->mutex, &ima_iint_mutex_key[depth],
+ nested);
#endif
}
static void ima_iint_init_always(struct ima_iint_cache *iint,
- struct inode *inode)
+ struct inode *inode, bool nested)
{
iint->ima_hash = NULL;
iint->version = 0;
@@ -69,7 +73,7 @@ static void ima_iint_init_always(struct ima_iint_cache *iint,
iint->ima_creds_status = INTEGRITY_UNKNOWN;
iint->measured_pcrs = 0;
mutex_init(&iint->mutex);
- ima_iint_lockdep_annotate(iint, inode);
+ ima_iint_lockdep_annotate(iint, inode, nested);
}
static void ima_iint_free(struct ima_iint_cache *iint)
@@ -82,13 +86,14 @@ static void ima_iint_free(struct ima_iint_cache *iint)
/**
* ima_inode_get - Find or allocate an iint associated with an inode
* @inode: Pointer to the inode
+ * @nested: Whether or not the iint->mutex lock can be nested
*
* Find an iint associated with an inode, and allocate a new one if not found.
* Caller must lock i_mutex.
*
* Return: An iint on success, NULL on error.
*/
-struct ima_iint_cache *ima_inode_get(struct inode *inode)
+struct ima_iint_cache *ima_inode_get(struct inode *inode, bool nested)
{
struct ima_iint_cache *iint;
@@ -100,7 +105,7 @@ struct ima_iint_cache *ima_inode_get(struct inode *inode)
if (!iint)
return NULL;
- ima_iint_init_always(iint, inode);
+ ima_iint_init_always(iint, inode, nested);
inode->i_flags |= S_IMA;
ima_inode_set_iint(inode, iint);
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 780627b0cde7..18285fc8ac07 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -248,7 +248,7 @@ static int process_measurement(struct file *file, const struct cred *cred,
inode_lock(inode);
if (action) {
- iint = ima_inode_get(inode);
+ iint = ima_inode_get(inode, func == DIGEST_LIST_CHECK);
if (!iint)
rc = -ENOMEM;
}
@@ -699,7 +699,7 @@ static void ima_post_create_tmpfile(struct mnt_idmap *idmap,
return;
/* Nothing to do if we can't allocate memory */
- iint = ima_inode_get(inode);
+ iint = ima_inode_get(inode, false);
if (!iint)
return;
@@ -731,7 +731,7 @@ static void ima_post_path_mknod(struct mnt_idmap *idmap, struct dentry *dentry)
return;
/* Nothing to do if we can't allocate memory */
- iint = ima_inode_get(inode);
+ iint = ima_inode_get(inode, false);
if (!iint)
return;
--
2.34.1
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