From 57d2ac2f90f124f0b471404fa5178bd6cef08f36 Mon Sep 17 00:00:00 2001
From: Kevin Lo <kevlo@FreeBSD.org>
Date: Sun, 22 May 2016 14:31:20 +0000
Subject: [PATCH] =?UTF-8?q?arc4random()=20returns=200=20to=20(2**32)?=
 =?UTF-8?q?=E2=88=921,=20use=20an=20alternative=20to=20initialize=20i=5Fge?=
 =?UTF-8?q?n=20if=20it's=20zero=20rather=20than=20a=20divide=20by=202.?=
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With inputs from  delphij, mckusick, rmacklem

Reviewed by:	mckusick
---
 sys/fs/ext2fs/ext2_alloc.c  | 3 ++-
 sys/fs/ext2fs/ext2_vfsops.c | 3 ++-
 sys/ufs/ffs/ffs_alloc.c     | 7 ++++---
 sys/ufs/ffs/ffs_vfsops.c    | 3 ++-
 4 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/sys/fs/ext2fs/ext2_alloc.c b/sys/fs/ext2fs/ext2_alloc.c
index c3bd29ba3c27..35e24c3bde24 100644
--- a/sys/fs/ext2fs/ext2_alloc.c
+++ b/sys/fs/ext2fs/ext2_alloc.c
@@ -408,7 +408,8 @@ ext2_valloc(struct vnode *pvp, int mode, struct ucred *cred, struct vnode **vpp)
 	/*
 	 * Set up a new generation number for this inode.
 	 */
-	ip->i_gen = arc4random();
+	while (ip->i_gen == 0 || ++ip->i_gen == 0)
+		ip->i_gen = arc4random();
 
 	vfs_timestamp(&ts);
 	ip->i_birthtime = ts.tv_sec;
diff --git a/sys/fs/ext2fs/ext2_vfsops.c b/sys/fs/ext2fs/ext2_vfsops.c
index 9f2b94c1e002..9f73357061de 100644
--- a/sys/fs/ext2fs/ext2_vfsops.c
+++ b/sys/fs/ext2fs/ext2_vfsops.c
@@ -998,7 +998,8 @@ ext2_vget(struct mount *mp, ino_t ino, int flags, struct vnode **vpp)
 	 * already have one. This should only happen on old filesystems.
 	 */
 	if (ip->i_gen == 0) {
-		ip->i_gen = random() + 1;
+		while (ip->i_gen == 0)
+			ip->i_gen = arc4random();
 		if ((vp->v_mount->mnt_flag & MNT_RDONLY) == 0)
 			ip->i_flag |= IN_MODIFIED;
 	}
diff --git a/sys/ufs/ffs/ffs_alloc.c b/sys/ufs/ffs/ffs_alloc.c
index 797a42b12354..0e4dc0316064 100644
--- a/sys/ufs/ffs/ffs_alloc.c
+++ b/sys/ufs/ffs/ffs_alloc.c
@@ -1102,8 +1102,8 @@ dup_alloc:
 	/*
 	 * Set up a new generation number for this inode.
 	 */
-	if (ip->i_gen == 0 || ++ip->i_gen == 0)
-		ip->i_gen = arc4random() / 2 + 1;
+	while (ip->i_gen == 0 || ++ip->i_gen == 0)
+		ip->i_gen = arc4random();
 	DIP_SET(ip, i_gen, ip->i_gen);
 	if (fs->fs_magic == FS_UFS2_MAGIC) {
 		vfs_timestamp(&ts);
@@ -2080,7 +2080,8 @@ gotit:
 		bzero(ibp->b_data, (int)fs->fs_bsize);
 		dp2 = (struct ufs2_dinode *)(ibp->b_data);
 		for (i = 0; i < INOPB(fs); i++) {
-			dp2->di_gen = arc4random() / 2 + 1;
+			while (dp2->di_gen == 0)
+				dp2->di_gen = arc4random();
 			dp2++;
 		}
 		/*
diff --git a/sys/ufs/ffs/ffs_vfsops.c b/sys/ufs/ffs/ffs_vfsops.c
index 7ecb053a7cc7..d644b73f4fb9 100644
--- a/sys/ufs/ffs/ffs_vfsops.c
+++ b/sys/ufs/ffs/ffs_vfsops.c
@@ -1768,7 +1768,8 @@ ffs_vgetf(mp, ino, flags, vpp, ffs_flags)
 	 * already have one. This should only happen on old filesystems.
 	 */
 	if (ip->i_gen == 0) {
-		ip->i_gen = arc4random() / 2 + 1;
+		while (ip->i_gen == 0)
+			ip->i_gen = arc4random();
 		if ((vp->v_mount->mnt_flag & MNT_RDONLY) == 0) {
 			ip->i_flag |= IN_MODIFIED;
 			DIP_SET(ip, i_gen, ip->i_gen);