Merge tag 'fix-fsmap-6.6_2023-09-12' of https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux into xfs-6.6-fixesA

xfs: fix fsmap cursor handling

This patchset addresses an integer overflow bug that Dave Chinner found
in how fsmap handles figuring out where in the record set we left off
when userspace calls back after the first call filled up all the
designated record space.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

* tag 'fix-fsmap-6.6_2023-09-12' of https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux:
  xfs: fix an agbno overflow in __xfs_getfsmap_datadev

Author: Chandan Babu R

fs/xfs/xfs_fsmap.c

@@ -565,6 +565,19 @@ xfs_getfsmap_rtdev_rtbitmap(
 }
 #endif /* CONFIG_XFS_RT */
 
+static inline bool
+rmap_not_shareable(struct xfs_mount *mp, const struct xfs_rmap_irec *r)
+{
+	if (!xfs_has_reflink(mp))
+		return true;
+	if (XFS_RMAP_NON_INODE_OWNER(r->rm_owner))
+		return true;
+	if (r->rm_flags & (XFS_RMAP_ATTR_FORK | XFS_RMAP_BMBT_BLOCK |
+			   XFS_RMAP_UNWRITTEN))
+		return true;
+	return false;
+}
+
 /* Execute a getfsmap query against the regular data device. */
 STATIC int
 __xfs_getfsmap_datadev(
@@ -598,7 +611,6 @@ __xfs_getfsmap_datadev(
 	 * low to the fsmap low key and max out the high key to the end
 	 * of the AG.
 	 */
-	info->low.rm_startblock = XFS_FSB_TO_AGBNO(mp, start_fsb);
 	info->low.rm_offset = XFS_BB_TO_FSBT(mp, keys[0].fmr_offset);
 	error = xfs_fsmap_owner_to_rmap(&info->low, &keys[0]);
 	if (error)
@@ -608,21 +620,20 @@ __xfs_getfsmap_datadev(
 
 	/* Adjust the low key if we are continuing from where we left off. */
 	if (info->low.rm_blockcount == 0) {
-		/* empty */
-	} else if (XFS_RMAP_NON_INODE_OWNER(info->low.rm_owner) ||
-		   (info->low.rm_flags & (XFS_RMAP_ATTR_FORK |
-					  XFS_RMAP_BMBT_BLOCK |
-					  XFS_RMAP_UNWRITTEN))) {
-		info->low.rm_startblock += info->low.rm_blockcount;
+		/* No previous record from which to continue */
+	} else if (rmap_not_shareable(mp, &info->low)) {
+		/* Last record seen was an unshareable extent */
 		info->low.rm_owner = 0;
 		info->low.rm_offset = 0;
 
 		start_fsb += info->low.rm_blockcount;
 		if (XFS_FSB_TO_DADDR(mp, start_fsb) >= eofs)
 			return 0;
 	} else {
+		/* Last record seen was a shareable file data extent */
 		info->low.rm_offset += info->low.rm_blockcount;
 	}
+	info->low.rm_startblock = XFS_FSB_TO_AGBNO(mp, start_fsb);
 
 	info->high.rm_startblock = -1U;
 	info->high.rm_owner = ULLONG_MAX;