[PATCH 6.12.y] dibs: loopback: validate offset and size in move_data()

[Dust Li <dust.li@linux.alibaba.com>]

commit 78237e3c0720fcc6eb9b87e90fd70f63eeca886f upstream.

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@vger.kernel.org
Reported-by: Federico Kirschbaum <federico.kirschbaum@xbow.com>
Signed-off-by: Dust Li <dust.li@linux.alibaba.com>
Reported-by: Baul Lee <baul.lee@xbow.com>
Link: https://patch.msgid.link/20260707074318.1448662-1-dust.li@linux.alibaba.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
(cherry picked from commit 78237e3c0720fcc6eb9b87e90fd70f63eeca886f)
[backport for smc_loopback instead of dibs_loopback]
Signed-off-by: Dust Li <dust.li@linux.alibaba.com>
---
 net/smc/smc_loopback.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/smc/smc_loopback.c b/net/smc/smc_loopback.c
index 85f0b7853b17..0bf9e4075f03 100644
--- a/net/smc/smc_loopback.c
+++ b/net/smc/smc_loopback.c
@@ -245,6 +245,11 @@ static int smc_lo_move_data(struct smcd_dev *smcd, 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);
 	read_unlock_bh(&ldev->dmb_ht_lock);
 
-- 
2.43.7