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* [PATCH] lsm_audit,selinux: add exception handling for possible NULL audit buffers
@ 2021-07-12 23:48 Austin Kim
  2021-07-13  2:49 ` Paul Moore
  0 siblings, 1 reply; 3+ messages in thread
From: Austin Kim @ 2021-07-12 23:48 UTC (permalink / raw)
  To: paul, stephen.smalley.work, eparis, omosnace
  Cc: selinux, linux-kernel, austin.kim, kernel-team, austindh.kim

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

It is possible for audit_log_start() to return NULL on error.
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


^ permalink raw reply related	[flat|nested] 3+ messages in thread
* Re: [PATCH] lsm_audit,selinux: add exception handling for possible NULL audit buffers
  2021-07-12 23:48 [PATCH] lsm_audit,selinux: add exception handling for possible NULL audit buffers Austin Kim
@ 2021-07-13  2:49 ` Paul Moore
  2021-07-13  3:40   ` Austin Kim
  0 siblings, 1 reply; 3+ messages in thread
From: Paul Moore @ 2021-07-13  2:49 UTC (permalink / raw)
  To: Austin Kim
  Cc: Stephen Smalley, Eric Paris, Ondrej Mosnacek, selinux,
	linux-kernel, austin.kim, kernel-team

On Mon, Jul 12, 2021 at 7:48 PM Austin Kim <austindh.kim@gmail.com> wrote:
> From: Austin Kim <austin.kim@lge.com>
>
> It is possible for audit_log_start() to return NULL on error.
> So add exception handling for possible NULL audit buffers where
> return value can be handled from callers.

Hi.

The patch looks fine to me, but I think the description doesn't tell
the full story and I'm worried that people might misunderstand why
this patch is worthwhile.  I would suggest you revise the commit
description to explain that in these cases it is safe to return early
when audit_log_start() returns NULL because the only non-cleanup
processing left in these functions is to generate an audit record.
Returning early in these cases is a performance optimization and not a
correctness issue; the audit_log_*() functions can support being
passed a NULL audit_buffer argument.

> 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

-- 
paul moore
www.paul-moore.com

^ permalink raw reply	[flat|nested] 3+ messages in thread
* Re: [PATCH] lsm_audit,selinux: add exception handling for possible NULL audit buffers
  2021-07-13  2:49 ` Paul Moore
@ 2021-07-13  3:40   ` Austin Kim
  0 siblings, 0 replies; 3+ messages in thread
From: Austin Kim @ 2021-07-13  3:40 UTC (permalink / raw)
  To: Paul Moore
  Cc: Stephen Smalley, Eric Paris, Ondrej Mosnacek, selinux,
	Linux Kernel Mailing List, 김동현,
	kernel-team

2021년 7월 13일 (화) 오전 11:49, Paul Moore <paul@paul-moore.com>님이 작성:
>
> On Mon, Jul 12, 2021 at 7:48 PM Austin Kim <austindh.kim@gmail.com> wrote:
> > From: Austin Kim <austin.kim@lge.com>
> >
> > It is possible for audit_log_start() to return NULL on error.
> > So add exception handling for possible NULL audit buffers where
> > return value can be handled from callers.
>
> Hi.
>
> The patch looks fine to me, but I think the description doesn't tell
> the full story and I'm worried that people might misunderstand why
> this patch is worthwhile.  I would suggest you revise the commit
> description to explain that in these cases it is safe to return early
> when audit_log_start() returns NULL because the only non-cleanup
> processing left in these functions is to generate an audit record.

Thanks for valuable feedback.
Let me resend the patch with revised 'commit description',
as you recommended.

> Returning early in these cases is a performance optimization and not a
> correctness issue; the audit_log_*() functions can support being
> passed a NULL audit_buffer argument.
>
> > 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
>
> --
> paul moore
> www.paul-moore.com

^ permalink raw reply	[flat|nested] 3+ messages in thread
end of thread, other threads:[~2021-07-13  3:40 UTC | newest]

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2021-07-12 23:48 [PATCH] lsm_audit,selinux: add exception handling for possible NULL audit buffers Austin Kim
2021-07-13  2:49 ` Paul Moore
2021-07-13  3:40   ` Austin Kim

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