We only allow a partial read of the first record in an audit pipe

record queue, so move the offset field from the per-record
audit_pipe_entry structure to the audit_pipe structure.

Now that we support reading more than one record at a time, add a
new summary field to audit_pipe, ap_qbyteslen, which tracks the
total number of bytes present in a pipe, and return that (minus
the current offset) via FIONREAD and kqueue's data variable for
the pending byte count rather than the number of bytes remaining
in only the first record.

Add a number of asserts to confirm that these counts and offsets
following the expected rules.

MFC after:	2 months
Sponsored by:	Apple, Inc.

1 files changed, 28 insertions, 15 deletions

diff --git a/sys/security/audit/audit_pipe.c b/sys/security/audit/audit_pipe.c
index d86123e..3abdc71 100644
--- a/sys/security/audit/audit_pipe.c
+++ b/sys/security/audit/audit_pipe.c
@@ -85,7 +85,6 @@ static MALLOC_DEFINE(M_AUDIT_PIPE_PRESELECT, "audit_pipe_presel",
 struct audit_pipe_entry {
 	void				*ape_record;
 	u_int				 ape_record_len;
-	u_int				 ape_record_offset;
 	TAILQ_ENTRY(audit_pipe_entry)	 ape_queue;
 };
 
@@ -138,8 +137,17 @@ struct audit_pipe {
 	 */
 	struct cv			 ap_cv;
 
+	/*
+	 * Various queue-reated variables: qlen and qlimit are a count of
+	 * records in the queue; qbyteslen is the number of bytes of data
+	 * across all records, and qoffset is the amount read so far of the
+	 * first record in the queue.  The number of bytes available for
+	 * reading in the queue is qbyteslen - qoffset.
+	 */
 	u_int				 ap_qlen;
 	u_int				 ap_qlimit;
+	u_int				 ap_qbyteslen;
+	u_int				 ap_qoffset;
 
 	u_int64_t			 ap_inserts;	/* Records added. */
 	u_int64_t			 ap_reads;	/* Records read. */
@@ -474,11 +482,11 @@ audit_pipe_append(struct audit_pipe *ap, void *record, u_int record_len)
 
 	bcopy(record, ape->ape_record, record_len);
 	ape->ape_record_len = record_len;
-	ape->ape_record_offset = 0;
 
 	TAILQ_INSERT_TAIL(&ap->ap_queue, ape, ape_queue);
 	ap->ap_inserts++;
 	ap->ap_qlen++;
+	ap->ap_qbyteslen += ape->ape_record_len;
 	selwakeuppri(&ap->ap_selinfo, PSOCK);
 	KNOTE_LOCKED(&ap->ap_selinfo.si_note, 0);
 	if (ap->ap_flags & AUDIT_PIPE_ASYNC)
@@ -603,10 +611,14 @@ audit_pipe_flush(struct audit_pipe *ap)
 
 	while ((ape = TAILQ_FIRST(&ap->ap_queue)) != NULL) {
 		TAILQ_REMOVE(&ap->ap_queue, ape, ape_queue);
+		ap->ap_qbyteslen -= ape->ape_record_len;
 		audit_pipe_entry_free(ape);
 		ap->ap_qlen--;
 	}
-	KASSERT(ap->ap_qlen == 0, ("audit_pipe_free: ap_qlen"));
+	ap->ap_qoffset = 0;
+
+	KASSERT(ap->ap_qlen == 0, ("audit_pipe_free: ap_qbyteslen"));
+	KASSERT(ap->ap_qbyteslen == 0, ("audit_pipe_flush: ap_qbyteslen"));
 }
 
 /*
@@ -752,12 +764,7 @@ audit_pipe_ioctl(struct cdev *dev, u_long cmd, caddr_t data, int flag,
 
 	case FIONREAD:
 		AUDIT_PIPE_LOCK(ap);
-		if (TAILQ_FIRST(&ap->ap_queue) != NULL)
-			*(int *)data =
-			    TAILQ_FIRST(&ap->ap_queue)->ape_record_len -
-			    TAILQ_FIRST(&ap->ap_queue)->ape_record_offset;
-		else
-			*(int *)data = 0;
+		*(int *)data = ap->ap_qbyteslen - ap->ap_qoffset;
 		AUDIT_PIPE_UNLOCK(ap);
 		error = 0;
 		break;
@@ -977,11 +984,13 @@ audit_pipe_read(struct cdev *dev, struct uio *uio, int flag)
 	    uio->uio_resid > 0) {
 		AUDIT_PIPE_LOCK_ASSERT(ap);
 
-		toread = MIN(ape->ape_record_len - ape->ape_record_offset,
+		KASSERT(ape->ape_record_len > ap->ap_qoffset,
+		    ("audit_pipe_read: record_len > qoffset (1)"));
+		toread = MIN(ape->ape_record_len - ap->ap_qoffset,
 		    uio->uio_resid);
 		AUDIT_PIPE_UNLOCK(ap);
-		error = uiomove((char *)ape->ape_record +
-		    ape->ape_record_offset, toread, uio);
+		error = uiomove((char *)ape->ape_record + ap->ap_qoffset,
+		    toread, uio);
 		if (error) {
 			AUDIT_PIPE_SX_XUNLOCK(ap);
 			return (error);
@@ -994,11 +1003,15 @@ audit_pipe_read(struct cdev *dev, struct uio *uio, int flag)
 		AUDIT_PIPE_LOCK(ap);
 		KASSERT(TAILQ_FIRST(&ap->ap_queue) == ape,
 		    ("audit_pipe_read: queue out of sync after uiomove"));
-		ape->ape_record_offset += toread;
-		if (ape->ape_record_offset == ape->ape_record_len) {
+		ap->ap_qoffset += toread;
+		KASSERT(ape->ape_record_len >= ap->ap_qoffset,
+		    ("audit_pipe_read: record_len >= qoffset (2)"));
+		if (ap->ap_qoffset == ape->ape_record_len) {
 			TAILQ_REMOVE(&ap->ap_queue, ape, ape_queue);
+			ap->ap_qbyteslen -= ape->ape_record_len;
 			audit_pipe_entry_free(ape);
 			ap->ap_qlen--;
+			ap->ap_qoffset = 0;
 		}
 	}
 	AUDIT_PIPE_UNLOCK(ap);
@@ -1071,7 +1084,7 @@ audit_pipe_kqread(struct knote *kn, long hint)
 		ape = TAILQ_FIRST(&ap->ap_queue);
 		KASSERT(ape != NULL, ("audit_pipe_kqread: ape == NULL"));
 
-		kn->kn_data = ape->ape_record_len - ape->ape_record_offset;
+		kn->kn_data = ap->ap_qbyteslen - ap->ap_qoffset;
 		return (1);
 	} else {
 		kn->kn_data = 0;