xfs: make the calculation generic in xfs_sb_validate_fsb_count()

Instead of assuming that PAGE_SHIFT is always higher than the blocklog,
make the calculation generic so that page cache count can be calculated
correctly for LBS.

Signed-off-by: Pankaj Raghav <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Acked-by: Darrick J. Wong <[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Reviewed-by: Dave Chinner <[email protected]>
Reviewed-by: Daniel Gomez <[email protected]>
Reviewed-by: Hannes Reinecke <[email protected]>
Reviewed-by: Matthew Wilcox (Oracle) <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

Author: Panky-codes

fs/xfs/xfs_mount.c

@@ -132,11 +132,16 @@ xfs_sb_validate_fsb_count(
 	xfs_sb_t	*sbp,
 	uint64_t	nblocks)
 {
+	uint64_t		max_bytes;
+
 	ASSERT(PAGE_SHIFT >= sbp->sb_blocklog);
 	ASSERT(sbp->sb_blocklog >= BBSHIFT);
 
+	if (check_shl_overflow(nblocks, sbp->sb_blocklog, &max_bytes))
+		return -EFBIG;
+
 	/* Limited by ULONG_MAX of page cache index */
-	if (nblocks >> (PAGE_SHIFT - sbp->sb_blocklog) > ULONG_MAX)
+	if (max_bytes >> PAGE_SHIFT > ULONG_MAX)
 		return -EFBIG;
 	return 0;
 }