xfs: check directory bestfree information in the verifier

Create a variant of xfs_dir2_data_freefind that is suitable for use in a
verifier.  Because _freefind is called by the verifier, we simply
duplicate the _freefind function, convert the ASSERTs to return
__this_address, and modify the verifier to call our new function.  Once
we've made it impossible for directory blocks with bad bestfree data to
make it into the filesystem we can remove the DEBUG code from the
regular _freefind function.

Underlying argument: corruption of on-disk metadata should return
-EFSCORRUPTED instead of blowing ASSERTs.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

fs/xfs/libxfs/xfs_dir2_data.c

@@ -33,6 +33,11 @@
 #include "xfs_cksum.h"
 #include "xfs_log.h"
 
+static xfs_failaddr_t xfs_dir2_data_freefind_verify(
+		struct xfs_dir2_data_hdr *hdr, struct xfs_dir2_data_free *bf,
+		struct xfs_dir2_data_unused *dup,
+		struct xfs_dir2_data_free **bf_ent);
+
 /*
  * Check the consistency of the data block.
  * The input can also be a block-format directory.
@@ -147,6 +152,8 @@ __xfs_dir3_data_check(
 		 * doesn't need to be there.
 		 */
 		if (be16_to_cpu(dup->freetag) == XFS_DIR2_DATA_FREE_TAG) {
+			xfs_failaddr_t	fa;
+
 			if (lastfree != 0)
 				return __this_address;
 			if (endp < p + be16_to_cpu(dup->length))
@@ -154,7 +161,9 @@ __xfs_dir3_data_check(
 			if (be16_to_cpu(*xfs_dir2_data_unused_tag_p(dup)) !=
 			    (char *)dup - (char *)hdr)
 				return __this_address;
-			dfp = xfs_dir2_data_freefind(hdr, bf, dup);
+			fa = xfs_dir2_data_freefind_verify(hdr, bf, dup, &dfp);
+			if (fa)
+				return fa;
 			if (dfp) {
 				i = (int)(dfp - bf);
 				if ((freeseen & (1 << i)) != 0)
@@ -381,55 +390,79 @@ xfs_dir3_data_readahead(
 }
 
 /*
- * Given a data block and an unused entry from that block,
- * return the bestfree entry if any that corresponds to it.
+ * Find the bestfree entry that exactly coincides with unused directory space
+ * or a verifier error because the bestfree data are bad.
  */
-xfs_dir2_data_free_t *
-xfs_dir2_data_freefind(
-	struct xfs_dir2_data_hdr *hdr,		/* data block header */
-	struct xfs_dir2_data_free *bf,		/* bestfree table pointer */
-	struct xfs_dir2_data_unused *dup)	/* unused space */
+static xfs_failaddr_t
+xfs_dir2_data_freefind_verify(
+	struct xfs_dir2_data_hdr	*hdr,
+	struct xfs_dir2_data_free	*bf,
+	struct xfs_dir2_data_unused	*dup,
+	struct xfs_dir2_data_free	**bf_ent)
 {
-	xfs_dir2_data_free_t	*dfp;		/* bestfree entry */
-	xfs_dir2_data_aoff_t	off;		/* offset value needed */
-#ifdef DEBUG
-	int			matched;	/* matched the value */
-	int			seenzero;	/* saw a 0 bestfree entry */
-#endif
+	struct xfs_dir2_data_free	*dfp;
+	xfs_dir2_data_aoff_t		off;
+	bool				matched = false;
+	bool				seenzero = false;
 
+	*bf_ent = NULL;
 	off = (xfs_dir2_data_aoff_t)((char *)dup - (char *)hdr);
 
-#ifdef DEBUG
 	/*
 	 * Validate some consistency in the bestfree table.
 	 * Check order, non-overlapping entries, and if we find the
 	 * one we're looking for it has to be exact.
 	 */
-	ASSERT(hdr->magic == cpu_to_be32(XFS_DIR2_DATA_MAGIC) ||
-	       hdr->magic == cpu_to_be32(XFS_DIR3_DATA_MAGIC) ||
-	       hdr->magic == cpu_to_be32(XFS_DIR2_BLOCK_MAGIC) ||
-	       hdr->magic == cpu_to_be32(XFS_DIR3_BLOCK_MAGIC));
-	for (dfp = &bf[0], seenzero = matched = 0;
-	     dfp < &bf[XFS_DIR2_DATA_FD_COUNT];
-	     dfp++) {
+	for (dfp = &bf[0]; dfp < &bf[XFS_DIR2_DATA_FD_COUNT]; dfp++) {
 		if (!dfp->offset) {
-			ASSERT(!dfp->length);
-			seenzero = 1;
+			if (dfp->length)
+				return __this_address;
+			seenzero = true;
 			continue;
 		}
-		ASSERT(seenzero == 0);
+		if (seenzero)
+			return __this_address;
 		if (be16_to_cpu(dfp->offset) == off) {
-			matched = 1;
-			ASSERT(dfp->length == dup->length);
-		} else if (off < be16_to_cpu(dfp->offset))
-			ASSERT(off + be16_to_cpu(dup->length) <= be16_to_cpu(dfp->offset));
-		else
-			ASSERT(be16_to_cpu(dfp->offset) + be16_to_cpu(dfp->length) <= off);
-		ASSERT(matched || be16_to_cpu(dfp->length) >= be16_to_cpu(dup->length));
-		if (dfp > &bf[0])
-			ASSERT(be16_to_cpu(dfp[-1].length) >= be16_to_cpu(dfp[0].length));
+			matched = true;
+			if (dfp->length != dup->length)
+				return __this_address;
+		} else if (be16_to_cpu(dfp->offset) > off) {
+			if (off + be16_to_cpu(dup->length) >
+					be16_to_cpu(dfp->offset))
+				return __this_address;
+		} else {
+			if (be16_to_cpu(dfp->offset) +
+					be16_to_cpu(dfp->length) > off)
+				return __this_address;
+		}
+		if (!matched &&
+		    be16_to_cpu(dfp->length) < be16_to_cpu(dup->length))
+			return __this_address;
+		if (dfp > &bf[0] &&
+		    be16_to_cpu(dfp[-1].length) < be16_to_cpu(dfp[0].length))
+			return __this_address;
 	}
-#endif
+
+	/* Looks ok so far; now try to match up with a bestfree entry. */
+	*bf_ent = xfs_dir2_data_freefind(hdr, bf, dup);
+	return NULL;
+}
+
+/*
+ * Given a data block and an unused entry from that block,
+ * return the bestfree entry if any that corresponds to it.
+ */
+xfs_dir2_data_free_t *
+xfs_dir2_data_freefind(
+	struct xfs_dir2_data_hdr *hdr,		/* data block header */
+	struct xfs_dir2_data_free *bf,		/* bestfree table pointer */
+	struct xfs_dir2_data_unused *dup)	/* unused space */
+{
+	xfs_dir2_data_free_t	*dfp;		/* bestfree entry */
+	xfs_dir2_data_aoff_t	off;		/* offset value needed */
+
+	off = (xfs_dir2_data_aoff_t)((char *)dup - (char *)hdr);
+
 	/*
 	 * If this is smaller than the smallest bestfree entry,
 	 * it can't be there since they're sorted.