Re: [PATCH v35 26/29] Audit: Add record for multiple task security contexts
From: John Johansen <john.johansen@canonical.com>
Date: 2022-04-26 01:08:40
Also in:
lkml, selinux
On 4/18/22 07:59, Casey Schaufler wrote:
Create a new audit record AUDIT_MAC_TASK_CONTEXTS.
An example of the MAC_TASK_CONTEXTS (1420) record is:
type=MAC_TASK_CONTEXTS[1420]
msg=audit(1600880931.832:113)
subj_apparmor=unconfined
subj_smack=_
When an audit event includes a AUDIT_MAC_TASK_CONTEXTS record
the "subj=" field in other records in the event will be "subj=?".
An AUDIT_MAC_TASK_CONTEXTS record is supplied when the system has
multiple security modules that may make access decisions based
on a subject security context.
Functions are created to manage the skb list in the audit_buffer.
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>Besides moving the aux fns, and the whining below Reviewed-by: John Johansen <john.johansen@canonical.com>
quoted hunk ↗ jump to hunk
--- include/uapi/linux/audit.h | 1 + kernel/audit.c | 93 +++++++++++++++++++++++++++++++++++--- 2 files changed, 88 insertions(+), 6 deletions(-)diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h index 8eda133ca4c1..af0aaccfaf57 100644 --- a/include/uapi/linux/audit.h +++ b/include/uapi/linux/audit.h@@ -143,6 +143,7 @@ #define AUDIT_MAC_UNLBL_STCDEL 1417 /* NetLabel: del a static label */ #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_FIRST_KERN_ANOM_MSG 1700 #define AUDIT_LAST_KERN_ANOM_MSG 1799diff --git a/kernel/audit.c b/kernel/audit.c index 4d44c05053b0..8ed2d717c217 100644 --- a/kernel/audit.c +++ b/kernel/audit.c@@ -2175,8 +2175,61 @@ void audit_log_key(struct audit_buffer *ab, char *key) audit_log_format(ab, "(null)"); } +/** + * audit_buffer_aux_new - Add an aux record buffer to the skb list + * @ab: audit_buffer + * @type: message type + * + * Aux records are allocated and added to the skb list of + * the "main" record. The ab->skb is reset to point to the + * aux record on its creation. When the aux record in complete + * ab->skb has to be reset to point to the "main" record. + * This allows the audit_log_ functions to be ignorant of + * which kind of record it is logging to. It also avoids adding + * special data for aux records. + * + * On success ab->skb will point to the new aux record. + * Returns 0 on success, -ENOMEM should allocation fail. + */ +static int audit_buffer_aux_new(struct audit_buffer *ab, int type) +{ + WARN_ON(ab->skb != skb_peek(&ab->skb_list)); + + ab->skb = nlmsg_new(AUDIT_BUFSIZ, ab->gfp_mask); + if (!ab->skb) + goto err; + if (!nlmsg_put(ab->skb, 0, 0, type, 0, 0)) + goto err; + skb_queue_tail(&ab->skb_list, ab->skb); + + audit_log_format(ab, "audit(%llu.%03lu:%u): ", + (unsigned long long)ab->stamp.ctime.tv_sec, + ab->stamp.ctime.tv_nsec/1000000, + ab->stamp.serial); + + return 0; + +err: + kfree_skb(ab->skb); + ab->skb = skb_peek(&ab->skb_list); + return -ENOMEM; +} + +/** + * audit_buffer_aux_end - Switch back to the "main" record from an aux record + * @ab: audit_buffer + * + * Restores the "main" audit record to ab->skb. + */ +static void audit_buffer_aux_end(struct audit_buffer *ab) +{ + ab->skb = skb_peek(&ab->skb_list); +} + + int audit_log_task_context(struct audit_buffer *ab) { + int i; int error; struct lsmblob blob; struct lsmcontext context;@@ -2185,16 +2238,44 @@ int audit_log_task_context(struct audit_buffer *ab) if (!lsmblob_is_set(&blob)) return 0; - error = security_secid_to_secctx(&blob, &context, LSMBLOB_FIRST); + if (!lsm_multiple_contexts()) { + error = security_secid_to_secctx(&blob, &context, + LSMBLOB_FIRST); + if (error) { + if (error != -EINVAL) + goto error_path; + return 0; + } - if (error) { - if (error != -EINVAL) + audit_log_format(ab, " subj=%s", context.context); + security_release_secctx(&context); + } else { + /* Multiple LSMs provide contexts. Include an aux record. */ + audit_log_format(ab, " subj=?");
just me whining, you sure we can't just drop subj= here
+ error = audit_buffer_aux_new(ab, AUDIT_MAC_TASK_CONTEXTS);
+ if (error)
goto error_path;
- return 0;
+ for (i = 0; i < LSMBLOB_ENTRIES; i++) {
+ if (blob.secid[i] == 0)
+ continue;
+ error = security_secid_to_secctx(&blob, &context, i);
+ if (error) {
+ audit_log_format(ab, "%ssubj_%s=?",
+ i ? " " : "",
+ lsm_slot_to_name(i));
+ if (error != -EINVAL)
+ audit_panic("error in audit_log_task_context");
+ } else {
+ audit_log_format(ab, "%ssubj_%s=%s",
+ i ? " " : "",
+ lsm_slot_to_name(i),
+ context.context);
+ security_release_secctx(&context);
+ }
+ }
+ audit_buffer_aux_end(ab);
}
- audit_log_format(ab, " subj=%s", context.context);
- security_release_secctx(&context);
return 0;
error_path: