Make generation numbers unsigned and fill them using a random number

from the range [1..UINT_MAX] initially.  On inode re-use increment
and on wrap refill from the range [1..UINT_MAX-1] to avoid
assigning UINT_MAX (the original value). Zero still means uninitialized.
ok millert@

4 files changed, 15 insertions, 18 deletions

diff --git a/sys/ufs/ffs/ffs_alloc.c b/sys/ufs/ffs/ffs_alloc.c
index 4a3267b1d5f..cb0bfeda58a 100644
--- a/sys/ufs/ffs/ffs_alloc.c
+++ b/sys/ufs/ffs/ffs_alloc.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ffs_alloc.c,v 1.110 2020/02/21 11:13:55 otto Exp $	*/
+/*	$OpenBSD: ffs_alloc.c,v 1.111 2020/05/28 15:48:29 otto Exp $	*/
 /*	$NetBSD: ffs_alloc.c,v 1.11 1996/05/11 18:27:09 mycroft Exp $	*/
 
 /*
@@ -413,16 +413,13 @@ ffs_inode_alloc(struct inode *pip, mode_t mode, struct ucred *cred,
 
 	/*
 	 * Set up a new generation number for this inode.
-	 * XXX - just increment for now, this is wrong! (millert)
-	 *       Need a way to preserve randomization.
+	 * On wrap, we make sure to assign a number != 0 and != UINT_MAX
+	 * (the origial value).
 	 */
 	if (DIP(ip, gen) != 0)
 		DIP_ADD(ip, gen, 1);
-	if (DIP(ip, gen) == 0)
-		DIP_ASSIGN(ip, gen, arc4random() & INT_MAX);
-
-	if (DIP(ip, gen) == 0 || DIP(ip, gen) == -1)
-		DIP_ASSIGN(ip, gen, 1);	/* Shouldn't happen */
+	while (DIP(ip, gen) == 0)
+		DIP_ASSIGN(ip, gen, arc4random_uniform(UINT_MAX));
 
 	return (0);
 
@@ -1205,9 +1202,10 @@ gotit:
                 memset(ibp->b_data, 0, fs->fs_bsize);
                 dp2 = (struct ufs2_dinode *)(ibp->b_data);
 
-		/* Give each inode a positive generation number */
+		/* Give each inode a generation number */
                 for (i = 0; i < INOPB(fs); i++) {
-                        dp2->di_gen = (arc4random() & INT32_MAX) / 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 453111b39dd..b8a7b0a590b 100644
--- a/sys/ufs/ffs/ffs_vfsops.c
+++ b/sys/ufs/ffs/ffs_vfsops.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ffs_vfsops.c,v 1.183 2020/02/21 11:11:15 otto Exp $	*/
+/*	$OpenBSD: ffs_vfsops.c,v 1.184 2020/05/28 15:48:29 otto Exp $	*/
 /*	$NetBSD: ffs_vfsops.c,v 1.19 1996/02/09 22:22:26 christos Exp $	*/
 
 /*
@@ -1422,9 +1422,8 @@ retry:
 	 * already have one. This should only happen on old filesystems.
 	 */
 	if (DIP(ip, gen) == 0) {
-		DIP_ASSIGN(ip, gen, arc4random() & INT_MAX);
-		if (DIP(ip, gen) == 0 || DIP(ip, gen) == -1)
-			DIP_ASSIGN(ip, gen, 1);	/* Shouldn't happen */
+		while (DIP(ip, gen) == 0)
+			DIP_ASSIGN(ip, gen, arc4random());
 		if ((vp->v_mount->mnt_flag & MNT_RDONLY) == 0)
 			ip->i_flag |= IN_MODIFIED;
 	}
diff --git a/sys/ufs/ufs/dinode.h b/sys/ufs/ufs/dinode.h
index 5ad69be286e..7a2d55b45f2 100644
--- a/sys/ufs/ufs/dinode.h
+++ b/sys/ufs/ufs/dinode.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: dinode.h,v 1.18 2013/05/30 19:19:09 guenther Exp $	*/
+/*	$OpenBSD: dinode.h,v 1.19 2020/05/28 15:48:29 otto Exp $	*/
 /*	$NetBSD: dinode.h,v 1.7 1995/06/15 23:22:48 cgd Exp $	*/
 
 /*
@@ -82,7 +82,7 @@ struct	ufs1_dinode {
 	int32_t		di_ib[NIADDR];	/*  88: Indirect disk blocks. */
 	u_int32_t	di_flags;	/* 100: Status flags (chflags). */
 	int32_t		di_blocks;	/* 104: Blocks actually held. */
-	int32_t		di_gen;		/* 108: Generation number. */
+	u_int32_t	di_gen;		/* 108: Generation number. */
 	u_int32_t	di_uid;		/* 112: File owner. */
 	u_int32_t	di_gid;		/* 116: File group. */
 	int32_t		di_spare[2];	/* 120: Reserved; currently unused */
diff --git a/sys/ufs/ufs/inode.h b/sys/ufs/ufs/inode.h
index 4675dc7e38d..4530c4e304d 100644
--- a/sys/ufs/ufs/inode.h
+++ b/sys/ufs/ufs/inode.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: inode.h,v 1.51 2019/01/21 18:09:21 anton Exp $	*/
+/*	$OpenBSD: inode.h,v 1.52 2020/05/28 15:48:29 otto Exp $	*/
 /*	$NetBSD: inode.h,v 1.8 1995/06/15 23:22:50 cgd Exp $	*/
 
 /*
@@ -344,6 +344,6 @@ struct ufid {
 	u_int16_t ufid_len;	/* Length of structure. */
 	u_int16_t ufid_pad;	/* Force 32-bit alignment. */
 	ufsino_t  ufid_ino;	/* File number (ino). */
-	int32_t	  ufid_gen;	/* Generation number. */
+	u_int32_t ufid_gen;	/* Generation number. */
 };
 #endif /* _KERNEL */