[PATCH] integrity: check the return value of audit_log_start()

From: Xiaoke Wang <redacted>

audit_log_start() returns audit_buffer pointer on success or NULL on
error, so it is better to check the return value of it to prevent
potential memory access error.

Signed-off-by: Xiaoke Wang <redacted>
---
 security/integrity/integrity_audit.c | 38 +++++++++++++++-------------
 1 file changed, 20 insertions(+), 18 deletions(-)

diff --git a/security/integrity/integrity_audit.c b/security/integrity/integrity_audit.c
index 2922005..62785d5 100644
--- a/security/integrity/integrity_audit.c
+++ b/security/integrity/integrity_audit.c

@@ -45,23 +45,25 @@ void integrity_audit_message(int audit_msgno, struct inode *inode,
 		return;
 
 	ab = audit_log_start(audit_context(), GFP_KERNEL, audit_msgno);
-	audit_log_format(ab, "pid=%d uid=%u auid=%u ses=%u",
-			 task_pid_nr(current),
-			 from_kuid(&init_user_ns, current_uid()),
-			 from_kuid(&init_user_ns, audit_get_loginuid(current)),
-			 audit_get_sessionid(current));
-	audit_log_task_context(ab);
-	audit_log_format(ab, " op=%s cause=%s comm=", op, cause);
-	audit_log_untrustedstring(ab, get_task_comm(name, current));
-	if (fname) {
-		audit_log_format(ab, " name=");
-		audit_log_untrustedstring(ab, fname);
+	if (ab) {
+		audit_log_format(ab, "pid=%d uid=%u auid=%u ses=%u",
+				task_pid_nr(current),
+				from_kuid(&init_user_ns, current_uid()),
+				from_kuid(&init_user_ns, audit_get_loginuid(current)),
+				audit_get_sessionid(current));
+		audit_log_task_context(ab);
+		audit_log_format(ab, " op=%s cause=%s comm=", op, cause);
+		audit_log_untrustedstring(ab, get_task_comm(name, current));
+		if (fname) {
+			audit_log_format(ab, " name=");
+			audit_log_untrustedstring(ab, fname);
+		}
+		if (inode) {
+			audit_log_format(ab, " dev=");
+			audit_log_untrustedstring(ab, inode->i_sb->s_id);
+			audit_log_format(ab, " ino=%lu", inode->i_ino);
+		}
+		audit_log_format(ab, " res=%d errno=%d", !result, errno);
+		audit_log_end(ab);
 	}
-	if (inode) {
-		audit_log_format(ab, " dev=");
-		audit_log_untrustedstring(ab, inode->i_sb->s_id);
-		audit_log_format(ab, " ino=%lu", inode->i_ino);
-	}
-	audit_log_format(ab, " res=%d errno=%d", !result, errno);
-	audit_log_end(ab);
 }

-- 

On Tue, Dec 14, 2021 at 12:39 AM [off-list ref] wrote:

As this is IMA code, it's largely up to Mimi about what she would
prefer, but I think a much simpler patch would be to just return early
if ab == NULL, for example:

  ab = audit_log_start( .... , audit_msgno);
  if (!ab)
    return;

-       audit_log_format(ab, "pid=%d uid=%u auid=%u ses=%u",
-                        task_pid_nr(current),
-                        from_kuid(&init_user_ns, current_uid()),
-                        from_kuid(&init_user_ns, audit_get_loginuid(current)),
-                        audit_get_sessionid(current));
-       audit_log_task_context(ab);
-       audit_log_format(ab, " op=%s cause=%s comm=", op, cause);
-       audit_log_untrustedstring(ab, get_task_comm(name, current));
-       if (fname) {
-               audit_log_format(ab, " name=");
-               audit_log_untrustedstring(ab, fname);
+       if (ab) {
+               audit_log_format(ab, "pid=%d uid=%u auid=%u ses=%u",
+                               task_pid_nr(current),
+                               from_kuid(&init_user_ns, current_uid()),
+                               from_kuid(&init_user_ns, audit_get_loginuid(current)),
+                               audit_get_sessionid(current));
+               audit_log_task_context(ab);
+               audit_log_format(ab, " op=%s cause=%s comm=", op, cause);
+               audit_log_untrustedstring(ab, get_task_comm(name, current));
+               if (fname) {
+                       audit_log_format(ab, " name=");
+                       audit_log_untrustedstring(ab, fname);
+               }
+               if (inode) {
+                       audit_log_format(ab, " dev=");
+                       audit_log_untrustedstring(ab, inode->i_sb->s_id);
+                       audit_log_format(ab, " ino=%lu", inode->i_ino);
+               }
+               audit_log_format(ab, " res=%d errno=%d", !result, errno);
+               audit_log_end(ab);
        }
-       if (inode) {
-               audit_log_format(ab, " dev=");
-               audit_log_untrustedstring(ab, inode->i_sb->s_id);
-               audit_log_format(ab, " ino=%lu", inode->i_ino);
-       }
-       audit_log_format(ab, " res=%d errno=%d", !result, errno);
-       audit_log_end(ab);
 }
--

-- 
paul moore
www.paul-moore.com

On Wed, 2022-01-12 at 12:23 -0500, Paul Moore wrote:

On Tue, Dec 14, 2021 at 12:39 AM [off-list ref] wrote:

quoted

From: Xiaoke Wang <redacted>

audit_log_start() returns audit_buffer pointer on success or NULL on
error, so it is better to check the return value of it to prevent
potential memory access error.

Signed-off-by: Xiaoke Wang <redacted>
---
 security/integrity/integrity_audit.c | 38 +++++++++++++++-------------
 1 file changed, 20 insertions(+), 18 deletions(-)

diff --git a/security/integrity/integrity_audit.c b/security/integrity/integrity_audit.c
index 2922005..62785d5 100644
--- a/security/integrity/integrity_audit.c
+++ b/security/integrity/integrity_audit.c

@@ -45,23 +45,25 @@ void integrity_audit_message(int audit_msgno, struct inode *inode,
                return;

        ab = audit_log_start(audit_context(), GFP_KERNEL, audit_msgno);

As this is IMA code, it's largely up to Mimi about what she would
prefer, but I think a much simpler patch would be to just return early
if ab == NULL, for example:

  ab = audit_log_start( .... , audit_msgno);
  if (!ab)
    return;

Thanks, Paul.  Neither the linux-integrity mailing list nor I were
Cc'ed on this.  Looks like the IMA & EVM records in MAINTAINERS should
be updated to include the security/integrity directory.

thanks,

Mimi