[PATCH] md/raid10: fix divide-by-zero in setup_geo() with zero far_copies

[Junrui Luo]

setup_geo() extracts near_copies (nc) and far_copies (fc) from the
user-provided layout parameter without checking for zero. When fc=0
with the "improved" far set layout selected, 'geo->far_set_size =
disks / fc' triggers a divide-by-zero.

Validate nc and fc immediately after extraction, returning -1 if
either is zero.

Fixes: 475901aff158 ("MD RAID10: Improve redundancy for 'far' and 'offset' algorithms (part 1)")
Reported-by: Yuhao Jiang <danisjiang@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Junrui Luo <moonafterrain@xxxxxxxxxxx>
---
 drivers/md/raid10.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 0653b5d8545a..811ea3d23b80 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -3791,6 +3791,8 @@ static int setup_geo(struct geom *geo, struct mddev *mddev, enum geo_type new)
 	nc = layout & 255;
 	fc = (layout >> 8) & 255;
 	fo = layout & (1<<16);
+	if (!nc || !fc)
+		return -1;
 	geo->raid_disks = disks;
 	geo->near_copies = nc;
 	geo->far_copies = fc;

---
base-commit: 7aaa8047eafd0bd628065b15757d9b48c5f9c07d
change-id: 20260416-fixes-6ba978713ab3

Best regards,
-- 
Junrui Luo <moonafterrain@xxxxxxxxxxx>