Create a new function ffs_getcg() to read in and verify a cylinder

group. Change all code points that open-coded this functionality
to use the new function. This commit is a refactoring with no
change in functionality.

In the future this change allows more robust checking of cylinder
group reads along the lines discussed in the hardening UFS session
at BSDCan (retry I/O, add checksums, etc). For more detail see the
session notes at https://wiki.freebsd.org/DevSummit/201706/HardeningUFS

Reviewed by: kib

sys/ufs/ffs/ffs_alloc.c

@@ -1602,15 +1602,8 @@ ffs_fragextend(ip, cg, bprev, osize, nsize)
 		return (0);
 	}
 	UFS_UNLOCK(ump);
-	error = bread(ump->um_devvp, fsbtodb(fs, cgtod(fs, cg)),
-	    (int)fs->fs_cgsize, NOCRED, &bp);
-	if (error)
+	if ((error = ffs_getcg(fs, ump->um_devvp, cg, &bp, &cgp)) != 0)
 		goto fail;
-	cgp = (struct cg *)bp->b_data;
-	if (!cg_chkmagic(cgp))
-		goto fail;
-	bp->b_xflags |= BX_BKGRDWRITE;
-	cgp->cg_old_time = cgp->cg_time = time_second;
 	bno = dtogd(fs, bprev);
 	blksfree = cg_blksfree(cgp);
 	for (i = numfrags(fs, osize); i < frags; i++)
@@ -1680,16 +1673,9 @@ ffs_alloccg(ip, cg, bpref, size, rsize)
 	if (fs->fs_cs(fs, cg).cs_nbfree == 0 && size == fs->fs_bsize)
 		return (0);
 	UFS_UNLOCK(ump);
-	error = bread(ump->um_devvp, fsbtodb(fs, cgtod(fs, cg)),
-	    (int)fs->fs_cgsize, NOCRED, &bp);
-	if (error)
+	if ((error = ffs_getcg(fs, ump->um_devvp, cg, &bp, &cgp)) != 0 ||
+	   (cgp->cg_cs.cs_nbfree == 0 && size == fs->fs_bsize))
 		goto fail;
-	cgp = (struct cg *)bp->b_data;
-	if (!cg_chkmagic(cgp) ||
-	    (cgp->cg_cs.cs_nbfree == 0 && size == fs->fs_bsize))
-		goto fail;
-	bp->b_xflags |= BX_BKGRDWRITE;
-	cgp->cg_old_time = cgp->cg_time = time_second;
 	if (size == fs->fs_bsize) {
 		UFS_LOCK(ump);
 		blkno = ffs_alloccgblk(ip, bp, bpref, rsize);
@@ -1857,7 +1843,7 @@ ffs_clusteralloc(ip, cg, bpref, len)
 	struct cg *cgp;
 	struct buf *bp;
 	struct ufsmount *ump;
-	int i, run, bit, map, got;
+	int i, run, bit, map, got, error;
 	ufs2_daddr_t bno;
 	u_char *mapp;
 	int32_t *lp;
@@ -1868,13 +1854,10 @@ ffs_clusteralloc(ip, cg, bpref, len)
 	if (fs->fs_maxcluster[cg] < len)
 		return (0);
 	UFS_UNLOCK(ump);
-	if (bread(ump->um_devvp, fsbtodb(fs, cgtod(fs, cg)), (int)fs->fs_cgsize,
-	    NOCRED, &bp))
-		goto fail_lock;
-	cgp = (struct cg *)bp->b_data;
-	if (!cg_chkmagic(cgp))
-		goto fail_lock;
-	bp->b_xflags |= BX_BKGRDWRITE;
+	if ((error = ffs_getcg(fs, ump->um_devvp, cg, &bp, &cgp)) != 0) {
+		UFS_LOCK(ump);
+		return (0);
+	}
 	/*
 	 * Check to see if a cluster of the needed size (or bigger) is
 	 * available in this cylinder group.
@@ -1897,7 +1880,8 @@ ffs_clusteralloc(ip, cg, bpref, len)
 				break;
 		UFS_LOCK(ump);
 		fs->fs_maxcluster[cg] = i;
-		goto fail;
+		brelse(bp);
+		return (0);
 	}
 	/*
 	 * Search the cluster map to find a big enough cluster.
@@ -1933,8 +1917,11 @@ ffs_clusteralloc(ip, cg, bpref, len)
 			bit = 1;
 		}
 	}
-	if (got >= cgp->cg_nclusterblks)
-		goto fail_lock;
+	if (got >= cgp->cg_nclusterblks) {
+		UFS_LOCK(ump);
+		brelse(bp);
+		return (0);
+	}
 	/*
 	 * Allocate the cluster that we have found.
 	 */
@@ -1954,12 +1941,6 @@ ffs_clusteralloc(ip, cg, bpref, len)
 	UFS_UNLOCK(ump);
 	bdwrite(bp);
 	return (bno);
-
-fail_lock:
-	UFS_LOCK(ump);
-fail:
-	brelse(bp);
-	return (0);
 }
 
 static inline struct buf *
@@ -2005,21 +1986,16 @@ ffs_nodealloccg(ip, cg, ipref, mode, unused)
 	if (fs->fs_cs(fs, cg).cs_nifree == 0)
 		return (0);
 	UFS_UNLOCK(ump);
-	error = bread(ump->um_devvp, fsbtodb(fs, cgtod(fs, cg)),
-		(int)fs->fs_cgsize, NOCRED, &bp);
-	if (error) {
-		brelse(bp);
+	if ((error = ffs_getcg(fs, ump->um_devvp, cg, &bp, &cgp)) != 0) {
 		UFS_LOCK(ump);
 		return (0);
 	}
-	cgp = (struct cg *)bp->b_data;
 restart:
-	if (!cg_chkmagic(cgp) || cgp->cg_cs.cs_nifree == 0) {
+	if (cgp->cg_cs.cs_nifree == 0) {
 		brelse(bp);
 		UFS_LOCK(ump);
 		return (0);
 	}
-	bp->b_xflags |= BX_BKGRDWRITE;
 	inosused = cg_inosused(cgp);
 	if (ipref) {
 		ipref %= fs->fs_ipg;
@@ -2103,21 +2079,16 @@ ffs_nodealloccg(ip, cg, ipref, mode, unused)
 		 * to it, then leave it unchanged as the other thread
 		 * has already set it correctly.
 		 */
-		error = bread(ump->um_devvp, fsbtodb(fs, cgtod(fs, cg)),
-		    (int)fs->fs_cgsize, NOCRED, &bp);
+		error = ffs_getcg(fs, ump->um_devvp, cg, &bp, &cgp);
 		UFS_LOCK(ump);
 		ACTIVECLEAR(fs, cg);
 		UFS_UNLOCK(ump);
-		if (error != 0) {
-			brelse(bp);
+		if (error != 0)
 			return (error);
-		}
-		cgp = (struct cg *)bp->b_data;
 		if (cgp->cg_initediblk == old_initediblk)
 			cgp->cg_initediblk += INOPB(fs);
 		goto restart;
 	}
-	cgp->cg_old_time = cgp->cg_time = time_second;
 	cgp->cg_irotor = ipref;
 	UFS_LOCK(ump);
 	ACTIVECLEAR(fs, cg);
@@ -2160,7 +2131,7 @@ ffs_blkfree_cg(ump, fs, devvp, bno, size, inum, dephd)
 	struct buf *bp;
 	ufs1_daddr_t fragno, cgbno;
 	ufs2_daddr_t cgblkno;
-	int i, blk, frags, bbase;
+	int i, blk, frags, bbase, error;
 	u_int cg;
 	u_int8_t *blksfree;
 	struct cdev *dev;
@@ -2193,17 +2164,8 @@ ffs_blkfree_cg(ump, fs, devvp, bno, size, inum, dephd)
 		ffs_fserr(fs, inum, "bad block");
 		return;
 	}
-	if (bread(devvp, cgblkno, (int)fs->fs_cgsize, NOCRED, &bp)) {
-		brelse(bp);
+	if ((error = ffs_getcg(fs, devvp, cg, &bp, &cgp)) != 0)
 		return;
-	}
-	cgp = (struct cg *)bp->b_data;
-	if (!cg_chkmagic(cgp)) {
-		brelse(bp);
-		return;
-	}
-	bp->b_xflags |= BX_BKGRDWRITE;
-	cgp->cg_old_time = cgp->cg_time = time_second;
 	cgbno = dtogd(fs, bno);
 	blksfree = cg_blksfree(cgp);
 	UFS_LOCK(ump);
@@ -2408,14 +2370,9 @@ ffs_checkblk(ip, bno, size)
 	}
 	if ((u_int)bno >= fs->fs_size)
 		panic("ffs_checkblk: bad block %jd", (intmax_t)bno);
-	error = bread(ITODEVVP(ip), fsbtodb(fs, cgtod(fs, dtog(fs, bno))),
-		(int)fs->fs_cgsize, NOCRED, &bp);
+	error = ffs_getcg(fs, ITODEVVP(ip), dtog(fs, bno), &bp, &cgp);
 	if (error)
-		panic("ffs_checkblk: cg bread failed");
-	cgp = (struct cg *)bp->b_data;
-	if (!cg_chkmagic(cgp))
-		panic("ffs_checkblk: cg magic mismatch");
-	bp->b_xflags |= BX_BKGRDWRITE;
+		panic("ffs_checkblk: cylinder group read failed");
 	blksfree = cg_blksfree(cgp);
 	cgbno = dtogd(fs, bno);
 	if (size == fs->fs_bsize) {
@@ -2492,17 +2449,8 @@ ffs_freefile(ump, fs, devvp, ino, mode, wkhd)
 	if (ino >= fs->fs_ipg * fs->fs_ncg)
 		panic("ffs_freefile: range: dev = %s, ino = %ju, fs = %s",
 		    devtoname(dev), (uintmax_t)ino, fs->fs_fsmnt);
-	if ((error = bread(devvp, cgbno, (int)fs->fs_cgsize, NOCRED, &bp))) {
-		brelse(bp);
+	if ((error = ffs_getcg(fs, devvp, cg, &bp, &cgp)) != 0)
 		return (error);
-	}
-	cgp = (struct cg *)bp->b_data;
-	if (!cg_chkmagic(cgp)) {
-		brelse(bp);
-		return (0);
-	}
-	bp->b_xflags |= BX_BKGRDWRITE;
-	cgp->cg_old_time = cgp->cg_time = time_second;
 	inosused = cg_inosused(cgp);
 	ino %= fs->fs_ipg;
 	if (isclr(inosused, ino)) {
@@ -2535,6 +2483,7 @@ ffs_freefile(ump, fs, devvp, ino, mode, wkhd)
 
 /*
  * Check to see if a file is free.
+ * Used to check for allocated files in snapshots.
  */
 int
 ffs_checkfreefile(fs, devvp, ino)
@@ -2545,7 +2494,7 @@ ffs_checkfreefile(fs, devvp, ino)
 	struct cg *cgp;
 	struct buf *bp;
 	ufs2_daddr_t cgbno;
-	int ret;
+	int ret, error;
 	u_int cg;
 	u_int8_t *inosused;
 
@@ -2561,15 +2510,8 @@ ffs_checkfreefile(fs, devvp, ino)
 	}
 	if (ino >= fs->fs_ipg * fs->fs_ncg)
 		return (1);
-	if (bread(devvp, cgbno, (int)fs->fs_cgsize, NOCRED, &bp)) {
-		brelse(bp);
+	if ((error = ffs_getcg(fs, devvp, cg, &bp, &cgp)) != 0)
 		return (1);
-	}
-	cgp = (struct cg *)bp->b_data;
-	if (!cg_chkmagic(cgp)) {
-		brelse(bp);
-		return (1);
-	}
 	inosused = cg_inosused(cgp);
 	ino %= fs->fs_ipg;
 	ret = isclr(inosused, ino);
@@ -2644,6 +2586,39 @@ ffs_mapsearch(fs, cgp, bpref, allocsiz)
 	return (-1);
 }
 
+/*
+ * Fetch and verify a cylinder group.
+ */
+int
+ffs_getcg(fs, devvp, cg, bpp, cgpp)
+	struct fs *fs;
+	struct vnode *devvp;
+	u_int cg;
+	struct buf **bpp;
+	struct cg **cgpp;
+{
+	struct buf *bp;
+	struct cg *cgp;
+	int error;
+
+	*bpp = NULL;
+	*cgpp = NULL;
+	error = bread(devvp, fsbtodb(fs, cgtod(fs, cg)),
+	    (int)fs->fs_cgsize, NOCRED, &bp);
+	if (error != 0)
+		return (error);
+	cgp = (struct cg *)bp->b_data;
+	if (!cg_chkmagic(cgp) || cgp->cg_cgx != cg) {
+		brelse(bp);
+		return (EIO);
+	}
+	bp->b_xflags |= BX_BKGRDWRITE;
+	cgp->cg_old_time = cgp->cg_time = time_second;
+	*bpp = bp;
+	*cgpp = cgp;
+	return (0);
+}
+
 /*
  * Fserr prints the name of a filesystem with an error diagnostic.
  *

sys/ufs/ffs/ffs_extern.h

@@ -74,6 +74,8 @@ void	ffs_fragacct(struct fs *, int, int32_t [], int);
 int	ffs_freefile(struct ufsmount *, struct fs *, struct vnode *, ino_t,
 	    int, struct workhead *);
 void	ffs_fserr(struct fs *, ino_t, char *);
+int	ffs_getcg(struct fs *, struct vnode *, u_int, struct buf **,
+	    struct cg **);
 int	ffs_isblock(struct fs *, u_char *, ufs1_daddr_t);
 int	ffs_isfreeblock(struct fs *, u_char *, ufs1_daddr_t);
 void	ffs_load_inode(struct buf *, struct inode *, struct fs *, ino_t);

sys/ufs/ffs/ffs_snapshot.c

@@ -888,17 +888,8 @@ cgaccount(cg, vp, nbp, passno)
 
 	ip = VTOI(vp);
 	fs = ITOFS(ip);
-	error = bread(ITODEVVP(ip), fsbtodb(fs, cgtod(fs, cg)),
-	    (int)fs->fs_cgsize, KERNCRED, &bp);
-	if (error) {
-		brelse(bp);
+	if ((error = ffs_getcg(fs, ITODEVVP(ip), cg, &bp, &cgp)) != 0)
 		return (error);
-	}
-	cgp = (struct cg *)bp->b_data;
-	if (!cg_chkmagic(cgp)) {
-		brelse(bp);
-		return (EIO);
-	}
 	UFS_LOCK(ITOUMP(ip));
 	ACTIVESET(fs, cg);
 	/*

sys/ufs/ffs/ffs_vfsops.c

@@ -1863,12 +1863,9 @@ ffs_fhtovp(mp, fhp, flags, vpp)
 	if (fs->fs_magic != FS_UFS2_MAGIC)
 		return (ufs_fhtovp(mp, ufhp, flags, vpp));
 	cg = ino_to_cg(fs, ino);
-	error = bread(ump->um_devvp, fsbtodb(fs, cgtod(fs, cg)),
-		(int)fs->fs_cgsize, NOCRED, &bp);
-	if (error)
+	if ((error = ffs_getcg(fs, ump->um_devvp, cg, &bp, &cgp)) != 0)
 		return (error);
-	cgp = (struct cg *)bp->b_data;
-	if (!cg_chkmagic(cgp) || ino >= cg * fs->fs_ipg + cgp->cg_initediblk) {
+	if (ino >= cg * fs->fs_ipg + cgp->cg_initediblk) {
 		brelse(bp);
 		return (ESTALE);
 	}

sys/ufs/ufs/ufs_gjournal.c

@@ -86,16 +86,8 @@ ufs_gjournal_modref(struct vnode *vp, int count)
 	if ((u_int)ino >= fs->fs_ipg * fs->fs_ncg)
 		panic("ufs_gjournal_modref: range: dev = %s, ino = %lu, fs = %s",
 		    devtoname(dev), (u_long)ino, fs->fs_fsmnt);
-	if ((error = bread(devvp, cgbno, (int)fs->fs_cgsize, NOCRED, &bp))) {
-		brelse(bp);
+	if ((error = ffs_getcg(fs, devvp, cg, &bp, &cgp)) != 0)
 		return (error);
-	}
-	cgp = (struct cg *)bp->b_data;
-	if (!cg_chkmagic(cgp)) {
-		brelse(bp);
-		return (0);
-	}
-	bp->b_xflags |= BX_BKGRDWRITE;
 	cgp->cg_unrefs += count;
 	UFS_LOCK(ump);
 	fs->fs_unrefs += count;