xfs: validate that zoned RT devices are zone aligned

Garbage collection assumes all zones contain the full amount of blocks.
Mkfs already ensures this happens, but make the kernel check it as well
to avoid getting into trouble due to fuzzers or mkfs bugs.

Fixes: 2167eaa ("xfs: define the zoned on-disk format")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Cc: stable@vger.kernel.org # v6.15
Signed-off-by: Carlos Maiolino <cem@kernel.org>

Author: Christoph Hellwig

fs/xfs/libxfs/xfs_sb.c

@@ -301,6 +301,21 @@ xfs_validate_rt_geometry(
 	    sbp->sb_rbmblocks != xfs_expected_rbmblocks(sbp))
 		return false;
 
+	if (xfs_sb_is_v5(sbp) &&
+	    (sbp->sb_features_incompat & XFS_SB_FEAT_INCOMPAT_ZONED)) {
+		uint32_t		mod;
+
+		/*
+		 * Zoned RT devices must be aligned to the RT group size,
+		 * because garbage collection assumes that all zones have the
+		 * same size to avoid insane complexity if that weren't the
+		 * case.
+		 */
+		div_u64_rem(sbp->sb_rextents, sbp->sb_rgextents, &mod);
+		if (mod)
+			return false;
+	}
+
 	return true;
 }