[PATCH] ima: Fix use-after-free on a dentry's dname.name

[Stefan Berger <stefanb@xxxxxxxxxxxxx>]

->d_name.name can change on rename and the earlier value can be freed;
there are conditions sufficient to stabilize it (->d_lock on dentry,
->d_lock on its parent, ->i_rwsem exclusive on the parent's inode,
rename_lock), but none of those are met at any of the sites. Take a stable
snapshot of the name instead.

Link: https://lore.kernel.org/all/20240202182732.GE2087318@ZenIV/
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
---
 security/integrity/ima/ima_api.c          | 16 ++++++++++++----
 security/integrity/ima/ima_template_lib.c | 17 ++++++++++++++---
 2 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index b37d043d5748..1856981e33df 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -245,8 +245,8 @@ int ima_collect_measurement(struct ima_iint_cache *iint, struct file *file,
 	const char *audit_cause = "failed";
 	struct inode *inode = file_inode(file);
 	struct inode *real_inode = d_real_inode(file_dentry(file));
-	const char *filename = file->f_path.dentry->d_name.name;
 	struct ima_max_digest_data hash;
+	struct name_snapshot filename;
 	struct kstat stat;
 	int result = 0;
 	int length;
@@ -317,9 +317,13 @@ int ima_collect_measurement(struct ima_iint_cache *iint, struct file *file,
 		if (file->f_flags & O_DIRECT)
 			audit_cause = "failed(directio)";
 
+		take_dentry_name_snapshot(&filename, file->f_path.dentry);
+
 		integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode,
-				    filename, "collect_data", audit_cause,
-				    result, 0);
+				    filename.name.name, "collect_data",
+				    audit_cause, result, 0);
+
+		release_dentry_name_snapshot(&filename);
 	}
 	return result;
 }
@@ -432,6 +436,7 @@ void ima_audit_measurement(struct ima_iint_cache *iint,
  */
 const char *ima_d_path(const struct path *path, char **pathbuf, char *namebuf)
 {
+	struct name_snapshot filename;
 	char *pathname = NULL;
 
 	*pathbuf = __getname();
@@ -445,7 +450,10 @@ const char *ima_d_path(const struct path *path, char **pathbuf, char *namebuf)
 	}
 
 	if (!pathname) {
-		strscpy(namebuf, path->dentry->d_name.name, NAME_MAX);
+		take_dentry_name_snapshot(&filename, path->dentry);
+		strscpy(namebuf, filename.name.name, NAME_MAX);
+		release_dentry_name_snapshot(&filename);
+
 		pathname = namebuf;
 	}
 
diff --git a/security/integrity/ima/ima_template_lib.c b/security/integrity/ima/ima_template_lib.c
index 6cd0add524cd..3b2cb8f1002e 100644
--- a/security/integrity/ima/ima_template_lib.c
+++ b/security/integrity/ima/ima_template_lib.c
@@ -483,7 +483,10 @@ static int ima_eventname_init_common(struct ima_event_data *event_data,
 				     bool size_limit)
 {
 	const char *cur_filename = NULL;
+	struct name_snapshot filename;
 	u32 cur_filename_len = 0;
+	bool snapshot = false;
+	int ret;
 
 	BUG_ON(event_data->filename == NULL && event_data->file == NULL);
 
@@ -496,7 +499,10 @@ static int ima_eventname_init_common(struct ima_event_data *event_data,
 	}
 
 	if (event_data->file) {
-		cur_filename = event_data->file->f_path.dentry->d_name.name;
+		take_dentry_name_snapshot(&filename,
+					  event_data->file->f_path.dentry);
+		snapshot = true;
+		cur_filename = filename.name.name;
 		cur_filename_len = strlen(cur_filename);
 	} else
 		/*
@@ -505,8 +511,13 @@ static int ima_eventname_init_common(struct ima_event_data *event_data,
 		 */
 		cur_filename_len = IMA_EVENT_NAME_LEN_MAX;
 out:
-	return ima_write_template_field_data(cur_filename, cur_filename_len,
-					     DATA_FMT_STRING, field_data);
+	ret = ima_write_template_field_data(cur_filename, cur_filename_len,
+					    DATA_FMT_STRING, field_data);
+
+	if (snapshot)
+		release_dentry_name_snapshot(&filename);
+
+	return ret;
 }
 
 /*
-- 
2.43.0