[PATCH v3 4/9] xfs: distinguish between inobt and finobt magic values

Brian Foster
2019-02-04T14:52:34Z

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 | 16 +++++++---------
fs/xfs/xfs_buf.c | 19 +++++++++++++++++++
fs/xfs/xfs_buf.h | 2 ++
3 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_ialloc_btree.c b/fs/xfs/libxfs/xfs_ialloc_btree.c
index 798269eb4767..c2df1f89eec8 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 = { cpu_to_be32(XFS_IBT_MAGIC), cpu_to_be32(XFS_IBT_CRC_MAGIC) },
.verify_read = xfs_inobt_read_verify,
.verify_write = xfs_inobt_write_verify,
.verify_struct = xfs_inobt_verify,
@@ -335,6 +331,8 @@ const struct xfs_buf_ops xfs_inobt_buf_ops = {

const struct xfs_buf_ops xfs_finobt_buf_ops = {
.name = "xfs_finobt",
+ .magic = { cpu_to_be32(XFS_FIBT_MAGIC),
+ cpu_to_be32(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.c b/fs/xfs/xfs_buf.c
index 222b5260ed35..0481c19fe5ae 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -2204,3 +2204,22 @@ void xfs_buf_set_ref(struct xfs_buf *bp, int lru_ref)

atomic_set(&bp->b_lru_ref, lru_ref);
}
+
+/*
+ * Verify an on-disk magic value against the magic value specified in the
+ * verifier structure. The verifier magic is in disk byte order so the caller is
+ * expected to pass the value directly from disk.
+ */
+bool
+xfs_verify_magic(
+ struct xfs_buf *bp,
+ uint32_t dmagic)
+{
+ struct xfs_mount *mp = bp->b_target->bt_mount;
+ int idx;
+
+ idx = xfs_sb_version_hascrc(&mp->m_sb);
+ if (unlikely(WARN_ON(!bp->b_ops || !bp->b_ops->magic[idx])))
+ return false;
+ return dmagic == bp->b_ops->magic[idx];
+}
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index 1c436a85b71d..44f9423a1861 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]; /* v4 and v5 on disk magic values */
void (*verify_read)(struct xfs_buf *);
void (*verify_write)(struct xfs_buf *);
xfs_failaddr_t (*verify_struct)(struct xfs_buf *bp);
@@ -386,5 +387,6 @@ extern int xfs_setsize_buftarg(xfs_buftarg_t *, unsigned int);
#define xfs_readonly_buftarg(buftarg) bdev_read_only((buftarg)->bt_bdev)

int xfs_buf_reverify(struct xfs_buf *bp, const struct xfs_buf_ops *ops);
+bool xfs_verify_magic(struct xfs_buf *bp, uint32_t dmagic);

#endif /* __XFS_BUF_H__ */
--
2.17.2