xfs: create a predicate to verify per-AG extents

Create a predicate function to verify that a given agbno/blockcount pair
fit entirely within a single allocation group and don't suffer
mathematical overflows.  Refactor the existng open-coded logic; we're
going to add more calls to this function in the next patch.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

4 files changed, 19 insertions, 17 deletions

diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
index 517a138faa66..191b22b9a35b 100644
--- a/fs/xfs/libxfs/xfs_ag.h
+++ b/fs/xfs/libxfs/xfs_ag.h
@@ -133,6 +133,21 @@ xfs_verify_agbno(struct xfs_perag *pag, xfs_agblock_t agbno)
 	return true;
 }
 
+static inline bool
+xfs_verify_agbext(
+	struct xfs_perag	*pag,
+	xfs_agblock_t		agbno,
+	xfs_agblock_t		len)
+{
+	if (agbno + len <= agbno)
+		return false;
+
+	if (!xfs_verify_agbno(pag, agbno))
+		return false;
+
+	return xfs_verify_agbno(pag, agbno + len - 1);
+}
+
 /*
  * Verify that an AG inode number pointer neither points outside the AG
  * nor points at static metadata.
diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
index 6261599bb389..de79f5d07f65 100644
--- a/fs/xfs/libxfs/xfs_alloc.c
+++ b/fs/xfs/libxfs/xfs_alloc.c
@@ -263,11 +263,7 @@ xfs_alloc_get_rec(
 		goto out_bad_rec;
 
 	/* check for valid extent range, including overflow */
-	if (!xfs_verify_agbno(pag, *bno))
-		goto out_bad_rec;
-	if (*bno > *bno + *len)
-		goto out_bad_rec;
-	if (!xfs_verify_agbno(pag, *bno + *len - 1))
+	if (!xfs_verify_agbext(pag, *bno, *len))
 		goto out_bad_rec;
 
 	return 0;
diff --git a/fs/xfs/libxfs/xfs_refcount.c b/fs/xfs/libxfs/xfs_refcount.c
index 831353ba96dc..1a50ca53304a 100644
--- a/fs/xfs/libxfs/xfs_refcount.c
+++ b/fs/xfs/libxfs/xfs_refcount.c
@@ -135,11 +135,7 @@ xfs_refcount_get_rec(
 	}
 
 	/* check for valid extent range, including overflow */
-	if (!xfs_verify_agbno(pag, realstart))
-		goto out_bad_rec;
-	if (realstart > realstart + irec->rc_blockcount)
-		goto out_bad_rec;
-	if (!xfs_verify_agbno(pag, realstart + irec->rc_blockcount - 1))
+	if (!xfs_verify_agbext(pag, realstart, irec->rc_blockcount))
 		goto out_bad_rec;
 
 	if (irec->rc_refcount == 0 || irec->rc_refcount > MAXREFCOUNT)
diff --git a/fs/xfs/libxfs/xfs_rmap.c b/fs/xfs/libxfs/xfs_rmap.c
index 094dfc897ebc..b56aca1e7c66 100644
--- a/fs/xfs/libxfs/xfs_rmap.c
+++ b/fs/xfs/libxfs/xfs_rmap.c
@@ -235,13 +235,8 @@ xfs_rmap_get_rec(
 			goto out_bad_rec;
 	} else {
 		/* check for valid extent range, including overflow */
-		if (!xfs_verify_agbno(pag, irec->rm_startblock))
-			goto out_bad_rec;
-		if (irec->rm_startblock >
-				irec->rm_startblock + irec->rm_blockcount)
-			goto out_bad_rec;
-		if (!xfs_verify_agbno(pag,
-				irec->rm_startblock + irec->rm_blockcount - 1))
+		if (!xfs_verify_agbext(pag, irec->rm_startblock,
+					    irec->rm_blockcount))
 			goto out_bad_rec;
 	}