Redesign the externalization APIs from the MAC Framework to

the MAC policy modules to improve robustness against C string
bugs and vulnerabilities.  Following these revisions, all
string construction of labels for export to userspace (or
elsewhere) is performed using the sbuf API, which prevents
the consumer from having to perform laborious and intricate
pointer and buffer checks.  This substantially simplifies
the externalization logic, both at the MAC Framework level,
and in individual policies; this becomes especially useful
when policies export more complex label data, such as with
compartments in Biba and MLS.

Bundled in here are some other minor fixes associated with
externalization: including avoiding malloc while holding the
process mutex in mac_lomac, and hence avoid a failure mode
when printing labels during a downgrade operation due to
the removal of the M_NOWAIT case.

This has been running in the MAC development tree for about
three weeks without problems.

Obtained from:	TrustedBSD Project
Sponsored by: DARPA, Network Associates Laboratories

1 files changed, 20 insertions, 40 deletions

diff --git a/sys/security/mac/mac_pipe.c b/sys/security/mac/mac_pipe.c
index 79a12ec..0d6bf29 100644
--- a/sys/security/mac/mac_pipe.c
+++ b/sys/security/mac/mac_pipe.c
@@ -56,6 +56,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/mac.h>
 #include <sys/module.h>
 #include <sys/proc.h>
+#include <sys/sbuf.h>
 #include <sys/systm.h>
 #include <sys/sysproto.h>
 #include <sys/sysent.h>
@@ -398,65 +399,44 @@ mac_policy_list_unbusy(void)
 
 #define	MAC_EXTERNALIZE(type, label, elementlist, outbuf, 		\
     outbuflen) do {							\
-	char *curptr, *curptr_start, *element_name, *element_temp;	\
-	size_t left, left_start, len;					\
-	int claimed, first, first_start, ignorenotfound;		\
+	int claimed, first, ignorenotfound, savedlen;			\
+	char *element_name, *element_temp;				\
+	struct sbuf sb;							\
 									\
 	error = 0;							\
-	element_temp = elementlist;					\
-	curptr = outbuf;						\
-	curptr[0] = '\0';						\
-	left = outbuflen;						\
 	first = 1;							\
+	sbuf_new(&sb, outbuf, outbuflen, SBUF_FIXEDLEN);		\
+	element_temp = elementlist;					\
 	while ((element_name = strsep(&element_temp, ",")) != NULL) {	\
-		curptr_start = curptr;					\
-		left_start = left;					\
-		first_start = first;					\
 		if (element_name[0] == '?') {				\
 			element_name++;					\
 			ignorenotfound = 1;				\
-		} else							\
+		 } else							\
 			ignorenotfound = 0;				\
-		claimed = 0;						\
+		savedlen = sbuf_len(&sb);				\
 		if (first) {						\
-			len = snprintf(curptr, left, "%s/",		\
-			    element_name);				\
+			error = sbuf_printf(&sb, "%s/", element_name);	\
 			first = 0;					\
 		} else							\
-			len = snprintf(curptr, left, ",%s/",		\
-			    element_name);				\
-		if (len >= left) {					\
-			error = EINVAL;		/* XXXMAC: E2BIG */	\
+			error = sbuf_printf(&sb, ",%s/", element_name);	\
+		if (error == -1) {					\
+			error = EINVAL;	/* XXX: E2BIG? */		\
 			break;						\
 		}							\
-		curptr += len;						\
-		left -= len;						\
-									\
+		claimed = 0;						\
 		MAC_CHECK(externalize_ ## type, label, element_name,	\
-		    curptr, left, &len, &claimed);			\
+		    &sb, &claimed);					\
 		if (error)						\
 			break;						\
-		if (claimed == 1) {					\
-			if (len >= outbuflen) {				\
-				error = EINVAL;	/* XXXMAC: E2BIG */	\
-				break;					\
-			}						\
-			curptr += len;					\
-			left -= len;					\
-		} else if (claimed == 0 && ignorenotfound) {		\
-			/*						\
-			 * Revert addition of the label element		\
-			 * name.					\
-			 */						\
-			curptr = curptr_start;				\
-			*curptr = '\0';					\
-			left = left_start;				\
-			first = first_start;				\
-		} else {						\
-			error = EINVAL;		/* XXXMAC: ENOLABEL */	\
+		if (claimed == 0 && ignorenotfound) {			\
+			/* Revert last label name. */			\
+			sbuf_setpos(&sb, savedlen);			\
+		} else if (claimed != 1) {				\
+			error = EINVAL;	/* XXX: ENOLABEL? */		\
 			break;						\
 		}							\
 	}								\
+	sbuf_finish(&sb);						\
 } while (0)
 
 #define	MAC_INTERNALIZE(type, label, instring) do {			\