[PATCH net] dibs: loopback: validate offset and size in move_data()

[Dust Li]

The loopback move_data() performs a memcpy into the registered DMB
without checking whether offset + size exceeds the DMB length.  Unlike
real ISM hardware, which enforces memory region bounds natively, the
software loopback has no such protection.

A peer-supplied out-of-bounds offset or oversized write would result in
an OOB write past the allocated kernel buffer.  Add an explicit bounds
check before the memcpy to reject such requests with -EINVAL.

Fixes: f7a22071dbf3("net/smc: implement DMB-related operations of loopback-ism")
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Federico Kirschbaum <federico.kirschbaum@xxxxxxxx>
Signed-off-by: Dust Li <dust.li@xxxxxxxxxxxxxxxxx>
---
 drivers/dibs/dibs_loopback.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/dibs/dibs_loopback.c b/drivers/dibs/dibs_loopback.c
index ec3b48cb0e87..0f2e09311152 100644
--- a/drivers/dibs/dibs_loopback.c
+++ b/drivers/dibs/dibs_loopback.c
@@ -254,6 +254,11 @@ static int dibs_lo_move_data(struct dibs_dev *dibs, u64 dmb_tok,
 		read_unlock_bh(&ldev->dmb_ht_lock);
 		return -EINVAL;
 	}
+	if ((u64)offset + size > rmb_node->len) {
+		read_unlock_bh(&ldev->dmb_ht_lock);
+		return -EINVAL;
+	}
+
 	memcpy((char *)rmb_node->cpu_addr + offset, data, size);
 	sba_idx = rmb_node->sba_idx;
 	read_unlock_bh(&ldev->dmb_ht_lock);
-- 
2.43.7