linux-kernel - [PATCH 2/3] ima: Ensure lock is held when setting iint pointer in inode security blob

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Message-Id: <20241008165732.2603647-2-roberto.sassu@huaweicloud.com>
Date: Tue,  8 Oct 2024 18:57:31 +0200
From: Roberto Sassu <roberto.sassu@...weicloud.com>
To: zohar@...ux.ibm.com,
	dmitry.kasatkin@...il.com,
	eric.snowberg@...cle.com,
	paul@...l-moore.com,
	jmorris@...ei.org,
	serge@...lyn.com
Cc: linux-integrity@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	bpf@...r.kernel.org,
	ebpqwerty472123@...il.com,
	Roberto Sassu <roberto.sassu@...wei.com>
Subject: [PATCH 2/3] ima: Ensure lock is held when setting iint pointer in inode security blob

From: Roberto Sassu <roberto.sassu@...wei.com>

IMA stores a pointer of the ima_iint_cache structure, containing integrity
metadata, in the inode security blob. However, check and assignment of this
pointer is not atomic, and it might happen that two tasks both see that the
iint pointer is NULL and try to set it, causing a memory leak.

Ensure that the iint check and assignment is guarded, by adding a lockdep
assertion in ima_inode_get().

Consequently, guard the remaining ima_inode_get() calls, in
ima_post_create_tmpfile() and ima_post_path_mknod(), to avoid the lockdep
warnings.

Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
---
 security/integrity/ima/ima_iint.c |  5 +++++
 security/integrity/ima/ima_main.c | 14 ++++++++++++--
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/security/integrity/ima/ima_iint.c b/security/integrity/ima/ima_iint.c
index c176fd0faae7..fe676ccec32f 100644
--- a/security/integrity/ima/ima_iint.c
+++ b/security/integrity/ima/ima_iint.c
@@ -87,8 +87,13 @@ static void ima_iint_free(struct ima_iint_cache *iint)
  */
 struct ima_iint_cache *ima_inode_get(struct inode *inode)
 {
+	struct ima_iint_cache_lock *iint_lock;
 	struct ima_iint_cache *iint;
 
+	iint_lock = ima_inode_security(inode->i_security);
+	if (iint_lock)
+		lockdep_assert_held(&iint_lock->mutex);
+
 	iint = ima_iint_find(inode);
 	if (iint)
 		return iint;
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 7852212c43ce..2425067b887d 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -705,14 +705,19 @@ static void ima_post_create_tmpfile(struct mnt_idmap *idmap,
 	if (!must_appraise)
 		return;
 
+	ima_iint_lock(inode);
+
 	/* Nothing to do if we can't allocate memory */
 	iint = ima_inode_get(inode);
-	if (!iint)
+	if (!iint) {
+		ima_iint_unlock(inode);
 		return;
+	}
 
 	/* needed for writing the security xattrs */
 	set_bit(IMA_UPDATE_XATTR, &iint->atomic_flags);
 	iint->ima_file_status = INTEGRITY_PASS;
+	ima_iint_unlock(inode);
 }
 
 /**
@@ -737,13 +742,18 @@ static void ima_post_path_mknod(struct mnt_idmap *idmap, struct dentry *dentry)
 	if (!must_appraise)
 		return;
 
+	ima_iint_lock(inode);
+
 	/* Nothing to do if we can't allocate memory */
 	iint = ima_inode_get(inode);
-	if (!iint)
+	if (!iint) {
+		ima_iint_unlock(inode);
 		return;
+	}
 
 	/* needed for re-opening empty files */
 	iint->flags |= IMA_NEW_FILE;
+	ima_iint_unlock(inode);
 }
 
 /**
-- 
2.34.1