[PATCH] ima: fallback to using i_version

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

Commit db1d1e8b9867 ("IMA: use vfs_getattr_nosec to get the i_version")
replaced detecting file change based on i_version with
STATX_CHANGE_COOKIE.

On filesystems without STATX_CHANGE_COOKIE enabled, revert back to
detecting file change based on i_version.

Fixes: db1d1e8b9867 ("IMA: use vfs_getattr_nosec to get the i_version")
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
---
 security/integrity/ima/ima_api.c  | 13 ++++++++----
 security/integrity/ima/ima_main.c | 34 +++++++++++++++++++++++++------
 2 files changed, 37 insertions(+), 10 deletions(-)

diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index c35ea613c9f8..3f0c73a8b459 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -267,15 +267,20 @@ int ima_collect_measurement(struct ima_iint_cache *iint, struct file *file,
 		goto out;
 
 	/*
-	 * Detecting file change is based on i_version. On filesystems
-	 * which do not support i_version, support was originally limited
-	 * to an initial measurement/appraisal/audit, but was modified to
-	 * assume the file changed.
+	 * Detect file change based on STATX_CHANGE_COOKIE, when supported,
+	 * and fallback to detecting file change based on i_version.
+	 *
+	 * On filesystems which did not support i_version, support was
+	 * originally limited to an initial measurement/appraisal/audit,
+	 * but was later modified to assume the file changed.
 	 */
 	result = vfs_getattr_nosec(&file->f_path, &stat, STATX_CHANGE_COOKIE,
 				   AT_STATX_SYNC_AS_STAT);
 	if (!result && (stat.result_mask & STATX_CHANGE_COOKIE))
 		i_version = stat.change_cookie;
+	else if (IS_I_VERSION(inode))
+		i_version = inode_peek_iversion(inode);
+
 	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 1d6229b156fb..fc50f727c954 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -184,7 +184,9 @@ static void ima_check_last_writer(struct ima_iint_cache *iint,
 				  struct inode *inode, struct file *file)
 {
 	fmode_t mode = file->f_mode;
+	int modified = 0;
 	bool update;
+	int result;
 
 	if (!(mode & FMODE_WRITE))
 		return;
@@ -197,12 +199,32 @@ static void ima_check_last_writer(struct ima_iint_cache *iint,
 
 		update = test_and_clear_bit(IMA_UPDATE_XATTR,
 					    &iint->atomic_flags);
-		if ((iint->flags & IMA_NEW_FILE) ||
-		    vfs_getattr_nosec(&file->f_path, &stat,
-				      STATX_CHANGE_COOKIE,
-				      AT_STATX_SYNC_AS_STAT) ||
-		    !(stat.result_mask & STATX_CHANGE_COOKIE) ||
-		    stat.change_cookie != iint->real_inode.version) {
+
+		if (iint->flags & IMA_NEW_FILE)
+			modified = 1;
+
+		/*
+		 * Detect file change based on STATX_CHANGE_COOKIE, when
+		 * supported, and fallback to detecting file change based
+		 * on i_version. On filesystems which do not support either,
+		 * assume the file changed.
+		 */
+		 result = vfs_getattr_nosec(&file->f_path, &stat,
+					    STATX_CHANGE_COOKIE,
+					    AT_STATX_SYNC_AS_STAT);
+
+		if (!result && stat.result_mask & STATX_CHANGE_COOKIE &&
+		    stat.change_cookie != iint->real_inode.version)
+			modified = 1;
+		else if (!(stat.result_mask & STATX_CHANGE_COOKIE) &&
+			 IS_I_VERSION(inode) &&
+			 !(inode_eq_iversion(inode, iint->real_inode.version)))
+			modified = 1;
+		else if (!(stat.result_mask & STATX_CHANGE_COOKIE) &&
+			 !(IS_I_VERSION(inode)))
+			modified = 1;
+
+		if (modified) {
 			iint->flags &= ~(IMA_DONE_MASK | IMA_NEW_FILE);
 			iint->measured_pcrs = 0;
 			if (update)
-- 
2.53.0