[PATCH v2 1/3] xfs: don't set bt_nr_sectors to a negative number

["Darrick J. Wong" <djwong@kernel.org>]

From: Darrick J. Wong <djwong@kernel.org>

xfs_daddr_t is a signed type, which means that xfs_buf_map_verify is
using a signed comparison.  This causes problems if bt_nr_sectors is
never overridden (e.g. in the case of an xfbtree for rmap btree repairs)
because even daddr 0 can't pass the verifier test in that case.

Define an explicit max constant and set the initial bt_nr_sectors to a
positive value.

Found by xfs/422.

Cc: <stable@vger.kernel.org> # v6.18-rc1
Fixes: 42852fe57c6d2a ("xfs: track the number of blocks in each buftarg")
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/xfs_buf.h |    1 +
 fs/xfs/xfs_buf.c |    2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index 8fa7bdf59c9110..e25cd2a160f31c 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -22,6 +22,7 @@ extern struct kmem_cache *xfs_buf_cache;
  */
 struct xfs_buf;
 
+#define XFS_BUF_DADDR_MAX	((xfs_daddr_t) S64_MAX)
 #define XFS_BUF_DADDR_NULL	((xfs_daddr_t) (-1LL))
 
 #define XBF_READ	 (1u << 0) /* buffer intended for reading from device */
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 773d959965dc29..47edf3041631bb 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1751,7 +1751,7 @@ xfs_init_buftarg(
 	const char			*descr)
 {
 	/* The maximum size of the buftarg is only known once the sb is read. */
-	btp->bt_nr_sectors = (xfs_daddr_t)-1;
+	btp->bt_nr_sectors = XFS_BUF_DADDR_MAX;
 
 	/* Set up device logical sector size mask */
 	btp->bt_logical_sectorsize = logical_sectorsize;