2021-07-14 00:12:30

by Austin Kim

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

From: Austin Kim <[email protected]>

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 <[email protected]>
---
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

2021-07-14 19:28:09

by Paul Moore

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

On Tue, Jul 13, 2021 at 8:11 PM Austin Kim <[email protected]> wrote:
>
> From: Austin Kim <[email protected]>
>
> 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 <[email protected]>
> ---
> security/selinux/hooks.c | 4 ++++
> security/selinux/ss/services.c | 2 ++
> 2 files changed, 6 insertions(+)

Merged into selinux/next, thank you!

--
paul moore
http://www.paul-moore.com

2021-07-14 22:25:53

by Austin Kim

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

2021년 7월 15일 (목) 오전 4:26, Paul Moore <[email protected]>님이 작성:
>
> On Tue, Jul 13, 2021 at 8:11 PM Austin Kim <[email protected]> wrote:
> >
> > From: Austin Kim <[email protected]>
> >
> > 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 <[email protected]>
> > ---
> > 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
> http://www.paul-moore.com