jail: Use flexible array member within struct prison_ip

Current implementation utilize off-by-one struct prison_ip to access the
IPv[46] addresses. It is error prone and hence comes the regression fix
21ad3e27fabc and ddbf879d79d4. Use flexible array member so that compiler
will catch such errors and it will also be easier to review.

No functional change intended.

Reviewed by:	melifaro, glebius
Differential Revision:	https://reviews.freebsd.org/D37874

1 files changed, 58 insertions, 44 deletions

diff --git a/sys/kern/kern_jail.c b/sys/kern/kern_jail.c
index b89c576b76ca..ba4fa6ea2ce4 100644
--- a/sys/kern/kern_jail.c
+++ b/sys/kern/kern_jail.c
@@ -576,16 +576,30 @@ struct prison_ip {
 	struct epoch_context ctx;
 	uint32_t	ips;
 #ifdef FUTURE_C
+	/*
+	 * XXX Variable-length automatic arrays in union may be
+	 * supported in future C.
+	 */
 	union {
+		char pr_ip[];
 		struct in_addr pr_ip4[];
 		struct in6_addr pr_ip6[];
 	};
 #else /* No future C :( */
-#define	PR_IP(pip, i)	((const char *)((pip) + 1) + pr_families[af].size * (i))
-#define	PR_IPD(pip, i)	((char *)((pip) + 1) + pr_families[af].size * (i))
+	char pr_ip[];
 #endif
 };
 
+static char *
+PR_IP(struct prison_ip *pip, const pr_family_t af, int idx)
+{
+	MPASS(pip);
+	MPASS(af < PR_FAMILY_MAX);
+	MPASS(idx >= 0 && idx < pip->ips);
+
+	return (pip->pr_ip + pr_families[af].size * idx);
+}
+
 static struct prison_ip *
 prison_ip_alloc(const pr_family_t af, uint32_t cnt, int flags)
 {
@@ -610,7 +624,7 @@ prison_ip_copyin(const pr_family_t af, void *op, uint32_t cnt)
 	struct prison_ip *pip;
 
 	pip = prison_ip_alloc(af, cnt, M_WAITOK);
-	bcopy(op, pip + 1, cnt * size);
+	bcopy(op, pip->pr_ip, cnt * size);
 	/*
 	 * IP addresses are all sorted but ip[0] to preserve
 	 * the primary IP address as given from userland.
@@ -620,21 +634,20 @@ prison_ip_copyin(const pr_family_t af, void *op, uint32_t cnt)
 	 * address to connect from.
 	 */
 	if (cnt > 1)
-		qsort((char *)(pip + 1) + size, cnt - 1, size,
-		    pr_families[af].cmp);
+		qsort(pip->pr_ip + size, cnt - 1, size, pr_families[af].cmp);
 	/*
 	 * Check for duplicate addresses and do some simple
 	 * zero and broadcast checks. If users give other bogus
 	 * addresses it is their problem.
 	 */
 	for (int i = 0; i < cnt; i++) {
-		if (!pr_families[af].valid(PR_IP(pip, i))) {
+		if (!pr_families[af].valid(PR_IP(pip, af, i))) {
 			free(pip, M_PRISON);
 			return (NULL);
 		}
 		if (i + 1 < cnt &&
-		    (cmp(PR_IP(pip, 0), PR_IP(pip, i + 1)) == 0 ||
-		     cmp(PR_IP(pip, i), PR_IP(pip, i + 1)) == 0)) {
+		    (cmp(PR_IP(pip, af, 0), PR_IP(pip, af, i + 1)) == 0 ||
+		     cmp(PR_IP(pip, af, i), PR_IP(pip, af, i + 1)) == 0)) {
 			free(pip, M_PRISON);
 			return (NULL);
 		}
@@ -654,7 +667,7 @@ prison_ip_dup(struct prison *ppr, struct prison *pr, const pr_family_t af)
 	if (ppr->pr_addrs[af] != NULL) {
 		pr->pr_addrs[af] = prison_ip_alloc(af,
 		    ppr->pr_addrs[af]->ips, M_WAITOK);
-		bcopy(ppr->pr_addrs[af] + 1, pr->pr_addrs[af] + 1,
+		bcopy(ppr->pr_addrs[af]->pr_ip, pr->pr_addrs[af]->pr_ip,
 		    pr->pr_addrs[af]->ips * pr_families[af].size);
 	}
 }
@@ -666,8 +679,8 @@ prison_ip_dup(struct prison *ppr, struct prison *pr, const pr_family_t af)
  * kern_jail_set() helper.
  */
 static bool
-prison_ip_parent_match(const struct prison_ip *ppip,
-    const struct prison_ip *pip, const pr_family_t af)
+prison_ip_parent_match(struct prison_ip *ppip, struct prison_ip *pip,
+    const pr_family_t af)
 {
 	prison_addr_cmp_t *const cmp = pr_families[af].cmp;
 	int i, j;
@@ -676,7 +689,7 @@ prison_ip_parent_match(const struct prison_ip *ppip,
 		return (false);
 
 	for (i = 0; i < ppip->ips; i++)
-		if (cmp(PR_IP(pip, 0), PR_IP(ppip, i)) == 0)
+		if (cmp(PR_IP(pip, af, 0), PR_IP(ppip, af, i)) == 0)
 			break;
 
 	if (i == ppip->ips)
@@ -685,11 +698,12 @@ prison_ip_parent_match(const struct prison_ip *ppip,
 
 	if (pip->ips > 1) {
 		for (i = j = 1; i < pip->ips; i++) {
-			if (cmp(PR_IP(pip, i), PR_IP(ppip, 0)) == 0)
+			if (cmp(PR_IP(pip, af, i), PR_IP(ppip, af, 0)) == 0)
 				/* Equals to parent primary address. */
 				continue;
 			for (; j < ppip->ips; j++)
-				if (cmp(PR_IP(pip, i), PR_IP(ppip, j)) == 0)
+				if (cmp(PR_IP(pip, af, i),
+				    PR_IP(ppip, af, j)) == 0)
 					break;
 			if (j == ppip->ips)
 				break;
@@ -709,7 +723,7 @@ prison_ip_parent_match(const struct prison_ip *ppip,
  */
 static bool
 prison_ip_conflict_check(const struct prison *ppr, const struct prison *pr,
-    const struct prison_ip *pip, pr_family_t af)
+    struct prison_ip *pip, pr_family_t af)
 {
 	const struct prison *tppr, *tpr;
 	int descend;
@@ -737,7 +751,7 @@ prison_ip_conflict_check(const struct prison *ppr, const struct prison *pr,
 		    (pip->ips == 1 && tpr->pr_addrs[af]->ips == 1))
 			continue;
 		for (int i = 0; i < pip->ips; i++)
-			if (prison_ip_check(tpr, af, PR_IP(pip, i)) == 0)
+			if (prison_ip_check(tpr, af, PR_IP(pip, af, i)) == 0)
 				return (false);
 	}
 
@@ -784,8 +798,8 @@ static bool
 prison_ip_restrict(struct prison *pr, const pr_family_t af,
     struct prison_ip **newp)
 {
-	const struct prison_ip *ppip = pr->pr_parent->pr_addrs[af];
-	const struct prison_ip *pip = pr->pr_addrs[af];
+	struct prison_ip *ppip = pr->pr_parent->pr_addrs[af];
+	struct prison_ip *pip = pr->pr_addrs[af];
 	int (*const cmp)(const void *, const void *) = pr_families[af].cmp;
 	const size_t size = pr_families[af].size;
 	struct prison_ip *new = newp != NULL ? *newp : NULL;
@@ -814,7 +828,7 @@ prison_ip_restrict(struct prison *pr, const pr_family_t af,
 		}
 		/* This has no user settings, so just copy the parent's list. */
 		MPASS(new->ips == ppip->ips);
-		bcopy(ppip + 1, new + 1, ppip->ips * size);
+		bcopy(ppip->pr_ip, new->pr_ip, ppip->ips * size);
 		prison_ip_set(pr, af, new);
 		if (newp != NULL)
 			*newp = NULL; /* Used */
@@ -832,30 +846,33 @@ prison_ip_restrict(struct prison *pr, const pr_family_t af,
 		}
 
 		for (int pi = 0; pi < ppip->ips; pi++)
-			if (cmp(PR_IP(pip, 0), PR_IP(ppip, pi)) == 0) {
+			if (cmp(PR_IP(pip, af, 0), PR_IP(ppip, af, pi)) == 0) {
 				/* Found our primary address in parent. */
-				bcopy(PR_IP(pip, i), PR_IPD(new, ips), size);
+				bcopy(PR_IP(pip, af, i), PR_IP(new, af, ips),
+				    size);
 				i++;
 				ips++;
 				break;
 			}
 		for (int pi = 1; i < pip->ips; ) {
 			/* Check against primary, which is unsorted. */
-			if (cmp(PR_IP(pip, i), PR_IP(ppip, 0)) == 0) {
+			if (cmp(PR_IP(pip, af, i), PR_IP(ppip, af, 0)) == 0) {
 				/* Matches parent's primary address. */
-				bcopy(PR_IP(pip, i), PR_IPD(new, ips), size);
+				bcopy(PR_IP(pip, af, i), PR_IP(new, af, ips),
+				    size);
 				i++;
 				ips++;
 				continue;
 			}
 			/* The rest are sorted. */
 			switch (pi >= ppip->ips ? -1 :
-				cmp(PR_IP(pip, i), PR_IP(ppip, pi))) {
+				cmp(PR_IP(pip, af, i), PR_IP(ppip, af, pi))) {
 			case -1:
 				i++;
 				break;
 			case 0:
-				bcopy(PR_IP(pip, i), PR_IPD(new, ips), size);
+				bcopy(PR_IP(pip, af, i), PR_IP(new, af, ips),
+				    size);
 				i++;
 				pi++;
 				ips++;
@@ -890,7 +907,7 @@ prison_ip_check(const struct prison *pr, const pr_family_t af,
     const void *addr)
 {
 	int (*const cmp)(const void *, const void *) = pr_families[af].cmp;
-	const struct prison_ip *pip;
+	struct prison_ip *pip;
 	int i, a, z, d;
 
 	MPASS(mtx_owned(&pr->pr_mtx) ||
@@ -902,7 +919,7 @@ prison_ip_check(const struct prison *pr, const pr_family_t af,
 		return (EAFNOSUPPORT);
 
 	/* Check the primary IP. */
-	if (cmp(PR_IP(pip, 0), addr) == 0)
+	if (cmp(PR_IP(pip, af, 0), addr) == 0)
 		return (0);
 
 	/*
@@ -912,7 +929,7 @@ prison_ip_check(const struct prison *pr, const pr_family_t af,
 	z = pip->ips - 2;
 	while (a <= z) {
 		i = (a + z) / 2;
-		d = cmp(PR_IP(pip, i + 1), addr);
+		d = cmp(PR_IP(pip, af, i + 1), addr);
 		if (d > 0)
 			z = i - 1;
 		else if (d < 0)
@@ -937,7 +954,7 @@ prison_ip_get0(const struct prison *pr, const pr_family_t af)
 	mtx_assert(&pr->pr_mtx, MA_OWNED);
 	MPASS(pip);
 
-	return (pip + 1);
+	return (pip->pr_ip);
 }
 
 u_int
@@ -2372,14 +2389,14 @@ kern_jail_get(struct thread *td, struct uio *optuio, int flags)
 	if (error != 0 && error != ENOENT)
 		goto done;
 #ifdef INET
-	error = vfs_setopt_part(opts, "ip4.addr", pr->pr_addrs[PR_INET] + 1,
+	error = vfs_setopt_part(opts, "ip4.addr", pr->pr_addrs[PR_INET]->pr_ip,
 	    pr->pr_addrs[PR_INET] ? pr->pr_addrs[PR_INET]->ips *
 	    pr_families[PR_INET].size : 0 );
 	if (error != 0 && error != ENOENT)
 		goto done;
 #endif
 #ifdef INET6
-	error = vfs_setopt_part(opts, "ip6.addr", pr->pr_addrs[PR_INET6] + 1,
+	error = vfs_setopt_part(opts, "ip6.addr", pr->pr_addrs[PR_INET6]->pr_ip,
 	    pr->pr_addrs[PR_INET6] ? pr->pr_addrs[PR_INET6]->ips *
 	    pr_families[PR_INET6].size : 0 );
 	if (error != 0 && error != ENOENT)
@@ -4194,7 +4211,7 @@ prison_ip_copyout(struct prison *pr, const pr_family_t af, void **out, int *len)
 			mtx_lock(&pr->pr_mtx);
 			goto again;
 		}
-		bcopy(pr->pr_addrs[af] + 1, *out, pr->pr_addrs[af]->ips * size);
+		bcopy(pr->pr_addrs[af]->pr_ip, *out, pr->pr_addrs[af]->ips * size);
 	}
 }
 #endif
@@ -4869,6 +4886,7 @@ db_show_prison(struct prison *pr)
 	struct jailsys_flags *jsf;
 #if defined(INET) || defined(INET6)
 	int ii;
+	struct prison_ip *pip;
 #endif
 	unsigned f;
 #ifdef INET
@@ -4928,28 +4946,24 @@ db_show_prison(struct prison *pr)
 	db_printf(" host.hostuuid   = %s\n", pr->pr_hostuuid);
 	db_printf(" host.hostid     = %lu\n", pr->pr_hostid);
 #ifdef INET
-	if (pr->pr_addrs[PR_INET] != NULL) {
-		pr_family_t af = PR_INET;
-
-		db_printf(" ip4s            = %d\n", pr->pr_addrs[af]->ips);
-		for (ii = 0; ii < pr->pr_addrs[af]->ips; ii++)
+	if ((pip = pr->pr_addrs[PR_INET]) != NULL) {
+		db_printf(" ip4s            = %d\n", pip->ips);
+		for (ii = 0; ii < pip->ips; ii++)
 			db_printf(" %s %s\n",
 			    ii == 0 ? "ip4.addr        =" : "                 ",
 			    inet_ntoa_r(
-			    *(const struct in_addr *)PR_IP(pr->pr_addrs[af], ii),
+			    *(const struct in_addr *)PR_IP(pip, PR_INET, ii),
 			    ip4buf));
 	}
 #endif
 #ifdef INET6
-	if (pr->pr_addrs[PR_INET6] != NULL) {
-		pr_family_t af = PR_INET6;
-
-		db_printf(" ip6s            = %d\n", pr->pr_addrs[af]->ips);
-		for (ii = 0; ii < pr->pr_addrs[af]->ips; ii++)
+	if ((pip = pr->pr_addrs[PR_INET6]) != NULL) {
+		db_printf(" ip6s            = %d\n", pip->ips);
+		for (ii = 0; ii < pip->ips; ii++)
 			db_printf(" %s %s\n",
 			    ii == 0 ? "ip6.addr        =" : "                 ",
 			    ip6_sprintf(ip6buf,
-			    (const struct in6_addr *)PR_IP(pr->pr_addrs[af], ii)));
+			    (const struct in6_addr *)PR_IP(pip, PR_INET6, ii)));
 	}
 #endif
 }