[PATCH v2] lsm_audit,selinux: return early for possible NULL audit buffers

[PATCH v2] lsm_audit,selinux: return early for possible NULL audit buffers

[Austin Kim]

From: Austin Kim <austin.kim@lge.com>

audit_log_start() may return NULL in below cases:

  - when audit is not initialized.
  - when audit backlog limit exceeds.

After the call to audit_log_start() is made and then possible NULL audit
buffer argument is passed to audit_log_*() functions, 
audit_log_*() functions return immediately in case of a NULL audit buffer 
argument.

But it is optimal to return early when audit_log_start() returns NULL,
because it is not necessary for audit_log_*() functions to be called with
NULL audit buffer argument.

So add exception handling for possible NULL audit buffers where
return value can be handled from callers.

Signed-off-by: Austin Kim <austin.kim@lge.com>
---
 security/selinux/hooks.c       | 4 ++++
 security/selinux/ss/services.c | 2 ++
 2 files changed, 6 insertions(+)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index b0032c42333e..9e84e6635f2f 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3325,6 +3325,8 @@ static int selinux_inode_setxattr(struct user_namespace *mnt_userns,
 			}
 			ab = audit_log_start(audit_context(),
 					     GFP_ATOMIC, AUDIT_SELINUX_ERR);
+			if (!ab)
+				return rc;
 			audit_log_format(ab, "op=setxattr invalid_context=");
 			audit_log_n_untrustedstring(ab, value, audit_size);
 			audit_log_end(ab);
@@ -6552,6 +6554,8 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
 				ab = audit_log_start(audit_context(),
 						     GFP_ATOMIC,
 						     AUDIT_SELINUX_ERR);
+				if (!ab)
+					return error;
 				audit_log_format(ab, "op=fscreate invalid_context=");
 				audit_log_n_untrustedstring(ab, value, audit_size);
 				audit_log_end(ab);
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index d84c77f370dc..e5f1b2757a83 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -1673,6 +1673,8 @@ static int compute_sid_handle_invalid_context(
 	if (context_struct_to_string(policydb, newcontext, &n, &nlen))
 		goto out;
 	ab = audit_log_start(audit_context(), GFP_ATOMIC, AUDIT_SELINUX_ERR);
+	if (!ab)
+		goto out;
 	audit_log_format(ab,
 			 "op=security_compute_sid invalid_context=");
 	/* no need to record the NUL with untrusted strings */
-- 
2.20.1

Re: [PATCH v2] lsm_audit,selinux: return early for possible NULL audit buffers

[Paul Moore]

On Tue, Jul 13, 2021 at 8:11 PM Austin Kim <austindh.kim@gmail.com> wrote:
>
> From: Austin Kim <austin.kim@lge.com>
>
> audit_log_start() may return NULL in below cases:
>
>   - when audit is not initialized.
>   - when audit backlog limit exceeds.
>
> After the call to audit_log_start() is made and then possible NULL audit
> buffer argument is passed to audit_log_*() functions,
> audit_log_*() functions return immediately in case of a NULL audit buffer
> argument.
>
> But it is optimal to return early when audit_log_start() returns NULL,
> because it is not necessary for audit_log_*() functions to be called with
> NULL audit buffer argument.
>
> So add exception handling for possible NULL audit buffers where
> return value can be handled from callers.
>
> Signed-off-by: Austin Kim <austin.kim@lge.com>
> ---
>  security/selinux/hooks.c       | 4 ++++
>  security/selinux/ss/services.c | 2 ++
>  2 files changed, 6 insertions(+)

Merged into selinux/next, thank you!

-- 
paul moore
www.paul-moore.com

Re: [PATCH v2] lsm_audit,selinux: return early for possible NULL audit buffers

[Austin Kim]

2021년 7월 15일 (목) 오전 4:26, Paul Moore <paul@paul-moore.com>님이 작성:
>
> On Tue, Jul 13, 2021 at 8:11 PM Austin Kim <austindh.kim@gmail.com> wrote:
> >
> > From: Austin Kim <austin.kim@lge.com>
> >
> > audit_log_start() may return NULL in below cases:
> >
> >   - when audit is not initialized.
> >   - when audit backlog limit exceeds.
> >
> > After the call to audit_log_start() is made and then possible NULL audit
> > buffer argument is passed to audit_log_*() functions,
> > audit_log_*() functions return immediately in case of a NULL audit buffer
> > argument.
> >
> > But it is optimal to return early when audit_log_start() returns NULL,
> > because it is not necessary for audit_log_*() functions to be called with
> > NULL audit buffer argument.
> >
> > So add exception handling for possible NULL audit buffers where
> > return value can be handled from callers.
> >
> > Signed-off-by: Austin Kim <austin.kim@lge.com>
> > ---
> >  security/selinux/hooks.c       | 4 ++++
> >  security/selinux/ss/services.c | 2 ++
> >  2 files changed, 6 insertions(+)
>
> Merged into selinux/next, thank you!

Great, thanks for review and feedback.

Thanks,
Austin Kim

>
> --
> paul moore
> www.paul-moore.com