[PATCH RFC v2 2/3] xfs: distinguish between inobt and finobt magic values

[Brian Foster <bfoster@redhat.com>]

The inode btree verifier code is shared between the inode btree and
free inode btree because the underlying metadata formats are
essentially equivalent. A side effect of this is that the verifier
cannot determine whether a particular btree block should have an
inobt or finobt magic value.

This logic allows an unfortunate xfs_repair bug to escape detection
where certain level > 0 nodes of the finobt are stamped with inobt
magic by xfs_repair finobt reconstruction. This is fortunately not a
severe problem since the inode btree magic values do not contribute
to any changes in kernel behavior, but we do need a means to detect
and prevent this problem in the future.

Add a field to xfs_buf_ops to store the v4 and v5 superblock magic
values expected by a particular verifier. Add a helper to check an
on-disk magic value against the value expected by the verifier. Call
the helper from the shared [f]inobt verifier code for magic value
verification. This ensures that the inode btree blocks each have the
appropriate magic value based on specific tree type and superblock
version.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/xfs/libxfs/xfs_ialloc_btree.c | 15 ++++++---------
 fs/xfs/xfs_buf.h                 | 19 +++++++++++++++++++
 2 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_ialloc_btree.c b/fs/xfs/libxfs/xfs_ialloc_btree.c
index 798269eb4767..c57ecb6b1255 100644
--- a/fs/xfs/libxfs/xfs_ialloc_btree.c
+++ b/fs/xfs/libxfs/xfs_ialloc_btree.c
@@ -260,6 +260,9 @@ xfs_inobt_verify(
 	xfs_failaddr_t		fa;
 	unsigned int		level;
 
+	if (!xfs_verify_magic(bp, block->bb_magic))
+		return __this_address;
+
 	/*
 	 * During growfs operations, we can't verify the exact owner as the
 	 * perag is not fully initialised and hence not attached to the buffer.
@@ -270,18 +273,10 @@ xfs_inobt_verify(
 	 * but beware of the landmine (i.e. need to check pag->pagi_init) if we
 	 * ever do.
 	 */
-	switch (block->bb_magic) {
-	case cpu_to_be32(XFS_IBT_CRC_MAGIC):
-	case cpu_to_be32(XFS_FIBT_CRC_MAGIC):
+	if (xfs_sb_version_hascrc(&mp->m_sb)) {
 		fa = xfs_btree_sblock_v5hdr_verify(bp);
 		if (fa)
 			return fa;
-		/* fall through */
-	case cpu_to_be32(XFS_IBT_MAGIC):
-	case cpu_to_be32(XFS_FIBT_MAGIC):
-		break;
-	default:
-		return __this_address;
 	}
 
 	/* level verification */
@@ -328,6 +323,7 @@ xfs_inobt_write_verify(
 
 const struct xfs_buf_ops xfs_inobt_buf_ops = {
 	.name = "xfs_inobt",
+	.magic = { XFS_IBT_MAGIC, XFS_IBT_CRC_MAGIC },
 	.verify_read = xfs_inobt_read_verify,
 	.verify_write = xfs_inobt_write_verify,
 	.verify_struct = xfs_inobt_verify,
@@ -335,6 +331,7 @@ const struct xfs_buf_ops xfs_inobt_buf_ops = {
 
 const struct xfs_buf_ops xfs_finobt_buf_ops = {
 	.name = "xfs_finobt",
+	.magic = { XFS_FIBT_MAGIC, XFS_FIBT_CRC_MAGIC },
 	.verify_read = xfs_inobt_read_verify,
 	.verify_write = xfs_inobt_write_verify,
 	.verify_struct = xfs_inobt_verify,
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index b9f5511ea998..d8757eafba71 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -125,6 +125,7 @@ struct xfs_buf_map {
 
 struct xfs_buf_ops {
 	char *name;
+	uint32_t magic[2];
 	void (*verify_read)(struct xfs_buf *);
 	void (*verify_write)(struct xfs_buf *);
 	xfs_failaddr_t (*verify_struct)(struct xfs_buf *bp);
@@ -387,4 +388,22 @@ extern int xfs_setsize_buftarg(xfs_buftarg_t *, unsigned int);
 
 int xfs_buf_ensure_ops(struct xfs_buf *bp, const struct xfs_buf_ops *ops);
 
+/*
+ * Verify an on-disk magic value against the magic value specified in the
+ * verifier structure.
+ */
+static inline bool
+xfs_buf_ops_verify_magic(
+	struct xfs_buf		*bp,
+	__be32			dmagic,
+	bool			crc)
+{
+	if (unlikely(WARN_ON(!bp->b_ops || !bp->b_ops->magic[crc])))
+		return false;
+	return dmagic == cpu_to_be32(bp->b_ops->magic[crc]);
+}
+#define xfs_verify_magic(bp, dmagic)		\
+	xfs_buf_ops_verify_magic(bp, dmagic,	\
+			xfs_sb_version_hascrc(&bp->b_target->bt_mount->m_sb))
+
 #endif	/* __XFS_BUF_H__ */
-- 
2.17.2