Do comprehensive UFS/FFS superblock integrity checks when reading a superblock.

Historically only minimal checks were made of a superblock when it
was read in as it was assumed that fsck would have been run to
correct any errors before attempting to use the filesystem. Recently
several bug reports have been submitted reporting kernel panics
that can be triggered by deliberately corrupting filesystem superblocks,
see Bug 263979 - [meta] UFS / FFS / GEOM crash (panic) tracking
which is tracking the reported corruption bugs.

This change upgrades the checks that are performed. These additional
checks should prevent panics from a corrupted superblock. Although
it appears in only one place, the new code will apply to the kernel
modules and (through libufs) user applications that read in superblocks.

Reported by:  Robert Morris and Neeraj
Reviewed by:  kib
Tested by:    Peter Holm
PR:           263979
MFC after:    1 month
Differential Revision: https://reviews.freebsd.org/D35219

sys/ufs/ffs/ffs_subr.c

@@ -35,6 +35,7 @@
 __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
+#include <sys/limits.h>
 
 #ifndef _KERNEL
 #include <stdio.h>
@@ -50,6 +51,7 @@ uint32_t ffs_calc_sbhash(struct fs *);
 struct malloc_type;
 #define UFS_MALLOC(size, type, flags) malloc(size)
 #define UFS_FREE(ptr, type) free(ptr)
+#define maxphys MAXPHYS
 
 #else /* _KERNEL */
 #include <sys/systm.h>
@@ -125,6 +127,7 @@ ffs_update_dinode_ckhash(struct fs *fs, struct ufs2_dinode *dip)
 static off_t sblock_try[] = SBLOCKSEARCH;
 static int readsuper(void *, struct fs **, off_t, int, int,
 	int (*)(void *, off_t, void **, int));
+static int validate_sblock(struct fs *, int);
 
 /*
  * Read a superblock from the devfd device.
@@ -141,7 +144,7 @@ static int readsuper(void *, struct fs **, off_t, int, int,
  *     EIO: non-existent or truncated superblock.
  *     EIO: error reading summary information.
  *     ENOENT: no usable known superblock found.
- *     ENOSPC: failed to allocate space for the superblock.
+ *     ENOMEM: failed to allocate space for the superblock.
  *     EINVAL: The previous newfs operation on this volume did not complete.
  *         The administrator must complete newfs before using this volume.
  */
@@ -152,7 +155,8 @@ ffs_sbget(void *devfd, struct fs **fsp, off_t altsblock,
 {
 	struct fs *fs;
 	struct fs_summary_info *fs_si;
-	int i, error, size, blks;
+	int i, error;
+	uint64_t size, blks;
 	uint8_t *space;
 	int32_t *lp;
 	char *buf;
@@ -190,17 +194,16 @@ ffs_sbget(void *devfd, struct fs **fsp, off_t altsblock,
 	if (fs->fs_contigsumsize > 0)
 		size += fs->fs_ncg * sizeof(int32_t);
 	size += fs->fs_ncg * sizeof(u_int8_t);
-	/* When running in libufs or libsa, UFS_MALLOC may fail */
-	if ((fs_si = UFS_MALLOC(sizeof(*fs_si), filltype, M_WAITOK)) == NULL) {
+	if ((fs_si = UFS_MALLOC(sizeof(*fs_si), filltype, M_NOWAIT)) == NULL) {
 		UFS_FREE(fs, filltype);
-		return (ENOSPC);
+		return (ENOMEM);
 	}
 	bzero(fs_si, sizeof(*fs_si));
 	fs->fs_si = fs_si;
-	if ((space = UFS_MALLOC(size, filltype, M_WAITOK)) == NULL) {
+	if ((space = UFS_MALLOC(size, filltype, M_NOWAIT)) == NULL) {
 		UFS_FREE(fs->fs_si, filltype);
 		UFS_FREE(fs, filltype);
-		return (ENOSPC);
+		return (ENOMEM);
 	}
 	fs->fs_csp = (struct csum *)space;
 	for (i = 0; i < blks; i += fs->fs_frag) {
@@ -253,16 +256,8 @@ readsuper(void *devfd, struct fs **fsp, off_t sblockloc, int isaltsblk,
 	fs = *fsp;
 	if (fs->fs_magic == FS_BAD_MAGIC)
 		return (EINVAL);
-	if (!(((fs->fs_magic == FS_UFS1_MAGIC && (isaltsblk ||
-	      sblockloc <= SBLOCK_UFS1)) ||
-	     (fs->fs_magic == FS_UFS2_MAGIC && (isaltsblk ||
-	      sblockloc == fs->fs_sblockloc))) &&
-	    fs->fs_ncg >= 1 &&
-	    fs->fs_bsize >= MINBSIZE &&
-	    fs->fs_bsize <= MAXBSIZE &&
-	    fs->fs_bsize >= roundup(sizeof(struct fs), DEV_BSIZE) &&
-	    fs->fs_sbsize <= SBLOCKSIZE))
-		return (ENOENT);
+	if ((error = validate_sblock(fs, isaltsblk)) != 0)
+		return (error);
 	/*
 	 * If the filesystem has been run on a kernel without
 	 * metadata check hashes, disable them.
@@ -310,6 +305,140 @@ readsuper(void *devfd, struct fs **fsp, off_t sblockloc, int isaltsblk,
 	return (0);
 }
 
+/*
+ * Verify the filesystem values.
+ */
+#define ILOG2(num) (fls(num) - 1)
+
+static int
+validate_sblock(struct fs *fs, int isaltsblk)
+{
+	int i, sectorsize;
+	u_int64_t maxfilesize, minfpg, sizepb;
+
+	sectorsize = dbtob(1);
+	if (fs->fs_magic == FS_UFS2_MAGIC) {
+		if ((!isaltsblk && (fs->fs_sblockloc != SBLOCK_UFS2 ||
+		    fs->fs_sblockactualloc != SBLOCK_UFS2)) ||
+		    fs->fs_maxsymlinklen != ((UFS_NDADDR + UFS_NIADDR) *
+			sizeof(ufs2_daddr_t)) ||
+		    fs->fs_nindir != fs->fs_bsize / sizeof(ufs2_daddr_t) ||
+		    fs->fs_inopb != fs->fs_bsize / sizeof(struct ufs2_dinode))
+			return (ENOENT);
+	} else if (fs->fs_magic == FS_UFS1_MAGIC) {
+		if ((!isaltsblk && (fs->fs_sblockloc > SBLOCK_UFS1 ||
+		    fs->fs_sblockactualloc != SBLOCK_UFS1)) ||
+		    fs->fs_nindir != fs->fs_bsize / sizeof(ufs1_daddr_t) ||
+		    fs->fs_inopb != fs->fs_bsize / sizeof(struct ufs1_dinode) ||
+		    fs->fs_maxsymlinklen != ((UFS_NDADDR + UFS_NIADDR) *
+			sizeof(ufs1_daddr_t)) ||
+		    fs->fs_old_inodefmt != FS_44INODEFMT ||
+		    fs->fs_old_cgoffset != 0 ||
+		    fs->fs_old_cgmask != 0xffffffff ||
+		    fs->fs_old_size != fs->fs_size ||
+		    fs->fs_old_rotdelay != 0 ||
+		    fs->fs_old_rps != 60 ||
+		    fs->fs_old_nspf != fs->fs_fsize / sectorsize ||
+		    fs->fs_old_cpg != 1 ||
+		    fs->fs_old_interleave != 1 ||
+		    fs->fs_old_trackskew != 0 ||
+		    fs->fs_old_cpc != 0 ||
+		    fs->fs_old_postblformat != 1 ||
+		    fs->fs_old_nrpos != 1 ||
+		    fs->fs_old_spc != fs->fs_fpg * fs->fs_old_nspf ||
+		    fs->fs_old_nsect != fs->fs_old_spc ||
+		    fs->fs_old_npsect != fs->fs_old_spc ||
+		    fs->fs_old_dsize != fs->fs_dsize ||
+		    fs->fs_old_ncyl != fs->fs_ncg)
+			return (ENOENT);
+	} else {
+		return (ENOENT);
+	}
+	if (fs->fs_bsize < MINBSIZE || fs->fs_bsize > MAXBSIZE ||
+	    fs->fs_bsize < roundup(sizeof(struct fs), DEV_BSIZE) ||
+	    fs->fs_sbsize > SBLOCKSIZE || fs->fs_sbsize < fs->fs_fsize ||
+	    !powerof2(fs->fs_bsize))
+		return (ENOENT);
+	if (fs->fs_fsize < sectorsize || fs->fs_fsize > fs->fs_bsize ||
+	    fs->fs_fsize * MAXFRAG < fs->fs_bsize || !powerof2(fs->fs_fsize))
+		return (ENOENT);
+	if (fs->fs_maxbsize < fs->fs_bsize || !powerof2(fs->fs_maxbsize) ||
+	    fs->fs_maxbsize > FS_MAXCONTIG * fs->fs_bsize)
+		return (ENOENT);
+	if (fs->fs_bmask != ~(fs->fs_bsize - 1) ||
+	    fs->fs_fmask != ~(fs->fs_fsize - 1) ||
+	    fs->fs_qbmask != ~fs->fs_bmask ||
+	    fs->fs_qfmask != ~fs->fs_fmask ||
+	    fs->fs_bshift != ILOG2(fs->fs_bsize) ||
+	    fs->fs_fshift != ILOG2(fs->fs_fsize) ||
+	    fs->fs_frag != numfrags(fs, fs->fs_bsize) ||
+	    fs->fs_fragshift != ILOG2(fs->fs_frag) ||
+	    fs->fs_frag > MAXFRAG ||
+	    fs->fs_fsbtodb != ILOG2(fs->fs_fsize / sectorsize))
+		return (ENOENT);
+	if (fs->fs_sblkno !=
+		roundup(howmany(fs->fs_sblockloc + SBLOCKSIZE, fs->fs_fsize),
+		    fs->fs_frag) ||
+	    fs->fs_cblkno != fs->fs_sblkno +
+		roundup(howmany(SBLOCKSIZE, fs->fs_fsize), fs->fs_frag) ||
+	    fs->fs_iblkno != fs->fs_cblkno + fs->fs_frag ||
+	    fs->fs_dblkno != fs->fs_iblkno + fs->fs_ipg / INOPF(fs) ||
+	    fs->fs_cgsize != fragroundup(fs, CGSIZE(fs)))
+		return (ENOENT);
+	if (fs->fs_csaddr != cgdmin(fs, 0) ||
+	    fs->fs_cssize !=
+		fragroundup(fs, fs->fs_ncg * sizeof(struct csum)) ||
+	    fs->fs_dsize != fs->fs_size - fs->fs_sblkno -
+		fs->fs_ncg * (fs->fs_dblkno - fs->fs_sblkno) -
+		howmany(fs->fs_cssize, fs->fs_fsize) ||
+	    fs->fs_metaspace < 0 || fs->fs_metaspace > fs->fs_fpg / 2 ||
+	    fs->fs_minfree > 99)
+		return (ENOENT);
+	maxfilesize = fs->fs_bsize * UFS_NDADDR - 1;
+	for (sizepb = fs->fs_bsize, i = 0; i < UFS_NIADDR; i++) {
+		sizepb *= NINDIR(fs);
+		maxfilesize += sizepb;
+	}
+	if (fs->fs_maxfilesize != maxfilesize)
+		return (ENOENT);
+	/*
+	 * These values have a tight interaction with each other that
+	 * makes it hard to tightly bound them. So we can only check
+	 * that they are within a broader possible range.
+	 *
+	 * Calculate minfpg, the minimum number of fragments that can be
+	 * in a cylinder group. The value 12289 is calculated in newfs(8)
+	 * when creating the smallest block size UFS version 1 filesystem
+	 * (4096 block size) with no fragments (4096 fragment size). That
+	 * number may be depressed even further for very small filesystems
+	 * since newfs(8) strives to have at least four cylinder groups.
+	 */
+	minfpg = MIN(12289, fs->fs_size / 4);
+	if (fs->fs_ncg < 1 || fs->fs_ncg > (fs->fs_size / minfpg) + 1 ||
+	    fs->fs_fpg < minfpg || fs->fs_fpg > fs->fs_size ||
+	    fs->fs_ipg * fs->fs_ncg > (((int64_t)(1)) << 32) - INOPB(fs) ||
+	    fs->fs_ipg > fs->fs_fpg || fs->fs_size < 8 * fs->fs_frag)
+		return (ENOENT);
+	if (fs->fs_size <= (fs->fs_ncg - 1) * fs->fs_fpg ||
+	    fs->fs_size > fs->fs_ncg * fs->fs_fpg)
+		return (ENOENT);
+	/*
+	 * Maxcontig sets the default for the maximum number of blocks
+	 * that may be allocated sequentially. With file system clustering
+	 * it is possible to allocate contiguous blocks up to the maximum
+	 * transfer size permitted by the controller or buffering.
+	 */
+	if (fs->fs_maxcontig < 1 ||
+	    fs->fs_maxcontig > MAX(1, maxphys / fs->fs_bsize))
+		return (ENOENT);
+	if (fs->fs_maxcontig < 0 ||
+	    (fs->fs_maxcontig == 0 && fs->fs_contigsumsize != 0) ||
+	    (fs->fs_maxcontig > 1 &&
+	    fs->fs_contigsumsize != MIN(fs->fs_maxcontig, FS_MAXCONTIG)))
+		return (ENOENT);
+	return (0);
+}
+
 /*
  * Write a superblock to the devfd device from the memory pointed to by fs.
  * Write out the superblock summary information if it is present.