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Date: Tue, 15 Mar 2022 19:47:50 -0400
From: Paul Moore <paul@...l-moore.com>
To: Casey Schaufler <casey@...aufler-ca.com>
Cc: casey.schaufler@...el.com, jmorris@...ei.org,
linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
linux-audit@...hat.com, keescook@...omium.org,
john.johansen@...onical.com, penguin-kernel@...ove.sakura.ne.jp,
stephen.smalley.work@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v33 27/29] Audit: Add record for multiple object security contexts
On Thu, Mar 10, 2022 at 7:01 PM Casey Schaufler <casey@...aufler-ca.com> wrote:
>
> Create a new audit record AUDIT_MAC_OBJ_CONTEXTS.
> An example of the MAC_OBJ_CONTEXTS (1421) record is:
>
> type=MAC_OBJ_CONTEXTS[1421]
> msg=audit(1601152467.009:1050):
> obj_selinux=unconfined_u:object_r:user_home_t:s0
>
> When an audit event includes a AUDIT_MAC_OBJ_CONTEXTS record
> the "obj=" field in other records in the event will be "obj=?".
> An AUDIT_MAC_OBJ_CONTEXTS record is supplied when the system has
> multiple security modules that may make access decisions based
> on an object security context.
>
> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
> ---
> include/linux/audit.h | 5 +++
> include/uapi/linux/audit.h | 1 +
> kernel/audit.c | 47 +++++++++++++++++++++++
> kernel/auditsc.c | 79 ++++++++++++--------------------------
> 4 files changed, 77 insertions(+), 55 deletions(-)
...
> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> index af0aaccfaf57..d25d76b29e3c 100644
> --- a/include/uapi/linux/audit.h
> +++ b/include/uapi/linux/audit.h
> @@ -144,6 +144,7 @@
> #define AUDIT_MAC_CALIPSO_ADD 1418 /* NetLabel: add CALIPSO DOI entry */
> #define AUDIT_MAC_CALIPSO_DEL 1419 /* NetLabel: del CALIPSO DOI entry */
> #define AUDIT_MAC_TASK_CONTEXTS 1420 /* Multiple LSM task contexts */
> +#define AUDIT_MAC_OBJ_CONTEXTS 1421 /* Multiple LSM objext contexts */
>
> #define AUDIT_FIRST_KERN_ANOM_MSG 1700
> #define AUDIT_LAST_KERN_ANOM_MSG 1799
> diff --git a/kernel/audit.c b/kernel/audit.c
> index ad825af203cf..ac92e7fc5aa6 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -2202,6 +2202,53 @@ static void audit_buffer_aux_end(struct audit_buffer *ab)
> ab->skb = skb_peek(&ab->skb_list);
> }
>
> +void audit_log_object_context(struct audit_buffer *ab, struct lsmblob *blob)
> +{
> + int i;
> + int error;
> + struct lsmcontext context;
> +
> + if (!lsm_multiple_contexts()) {
> + error = security_secid_to_secctx(blob, &context, LSMBLOB_FIRST);
> + if (error) {
> + if (error != -EINVAL)
> + goto error_path;
> + return;
> + }
> + audit_log_format(ab, " obj=%s", context.context);
> + security_release_secctx(&context);
> + } else {
> + audit_log_format(ab, " obj=?");
> + error = audit_buffer_aux_new(ab, AUDIT_MAC_OBJ_CONTEXTS);
> + if (error)
> + goto error_path;
> +
> + for (i = 0; i < LSMBLOB_ENTRIES; i++) {
> + if (blob->secid[i] == 0)
> + continue;
> + error = security_secid_to_secctx(blob, &context, i);
> + if (error) {
> + if (error != -EINVAL)
> + audit_panic("error in audit_log_object_context");
> + audit_log_format(ab, "%sobj_%s=?",
> + i ? " " : "",
> + lsm_slot_to_name(i));
> + } else {
> + audit_log_format(ab, "%sobj_%s=%s",
> + i ? " " : "",
> + lsm_slot_to_name(i),
> + context.context);
> + security_release_secctx(&context);
> + }
> + }
> +
> + audit_buffer_aux_end(ab);
> + }
> + return;
> +
> +error_path:
> + audit_panic("error in audit_log_object_context");
> +}
The comment from patch 26/29 regarding the audit_panic() placement
also applies to audit_log_object_context().
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 7848e7351cf9..923e4e3a5697 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -1114,36 +1114,25 @@ static inline void audit_free_context(struct audit_context *context)
> kfree(context);
> }
>
> -static int audit_log_pid_context(struct audit_context *context, pid_t pid,
> - kuid_t auid, kuid_t uid,
> - unsigned int sessionid,
> - struct lsmblob *blob, char *comm)
> +static void audit_log_pid_context(struct audit_context *context, pid_t pid,
> + kuid_t auid, kuid_t uid,
> + unsigned int sessionid,
> + struct lsmblob *blob, char *comm)
> {
> struct audit_buffer *ab;
> - struct lsmcontext lsmctx;
> - int rc = 0;
>
> ab = audit_log_start(context, GFP_KERNEL, AUDIT_OBJ_PID);
> if (!ab)
> - return rc;
> + return;
>
> audit_log_format(ab, "opid=%d oauid=%d ouid=%d oses=%d", pid,
> from_kuid(&init_user_ns, auid),
> from_kuid(&init_user_ns, uid), sessionid);
> - if (lsmblob_is_set(blob)) {
> - if (security_secid_to_secctx(blob, &lsmctx, LSMBLOB_FIRST)) {
> - audit_log_format(ab, " obj=(none)");
> - rc = 1;
> - } else {
> - audit_log_format(ab, " obj=%s", lsmctx.context);
> - security_release_secctx(&lsmctx);
> - }
> - }
> + if (lsmblob_is_set(blob))
> + audit_log_object_context(ab, blob);
> audit_log_format(ab, " ocomm=");
> audit_log_untrustedstring(ab, comm);
> audit_log_end(ab);
> -
> - return rc;
> }
>
> static void audit_log_execve_info(struct audit_context *context,
> @@ -1373,18 +1362,10 @@ static void show_special(struct audit_context *context, int *call_panic)
> from_kgid(&init_user_ns, context->ipc.gid),
> context->ipc.mode);
> if (osid) {
> - struct lsmcontext lsmcxt;
> struct lsmblob blob;
>
> lsmblob_init(&blob, osid);
> - if (security_secid_to_secctx(&blob, &lsmcxt,
> - LSMBLOB_FIRST)) {
> - audit_log_format(ab, " osid=%u", osid);
> - *call_panic = 1;
> - } else {
> - audit_log_format(ab, " obj=%s", lsmcxt.context);
> - security_release_secctx(&lsmcxt);
> - }
> + audit_log_object_context(ab, &blob);
While we lose the "osid=X" in case of failure, the secid/SID is a
private kernel value meaning it was always of questionable value.
--
paul-moore.com
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