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SubjectRe: [PATCH] lsm_audit,selinux: add exception handling for possible NULL audit buffers
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

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