[PATCH v2] i3c: master: svc: bound IBI payload to the requested max_payload_len

[Maoyi Xie]

svc_i3c_master_handle_ibi() reads the IBI payload from the RX FIFO into
the IBI slot. The loop is bounded by the hardware FIFO size
(SVC_I3C_FIFO_SIZE), not by the slot size.

slot->data points into the IBI pool, which i3c_generic_ibi_alloc_pool()
sizes at max_payload_len per slot. svc_i3c_master_request_ibi() only
rejects a max_payload_len larger than SVC_I3C_FIFO_SIZE, so a driver can
request a smaller one. mctp-i3c requests 1. Each readsb() then copies the
controller RXCOUNT bytes (up to 31) with no check against the slot size.
A device that sends more bytes than the slot holds writes past
slot->data, an out-of-bounds write into the IBI pool.

Bound the loop by dev->ibi->max_payload_len and clamp each read to the
space left in the slot, the same way dw-i3c does. A device can still send
more than the requested payload. Flush the leftover bytes from the RX FIFO
so they do not leak into the next transfer.

Fixes: dd3c52846d59 ("i3c: master: svc: Add Silvaco I3C master driver")
Cc: stable@xxxxxxxxxxxxxxx
Co-developed-by: Kaixuan Li <kaixuan.li@xxxxxxxxxx>
Signed-off-by: Kaixuan Li <kaixuan.li@xxxxxxxxxx>
Signed-off-by: Maoyi Xie <maoyixie.tju@xxxxxxxxx>
---
v2:
- use min() instead of min_t(), the types already match (Frank Li)
- flush the leftover RX FIFO bytes after the bounded read, so an
  oversized IBI does not desync the next transfer (Sashiko AI review)

 drivers/i3c/master/svc-i3c-master.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/i3c/master/svc-i3c-master.c b/drivers/i3c/master/svc-i3c-master.c
index e2d99a3ac07d..4eb54f9ee2cd 100644
--- a/drivers/i3c/master/svc-i3c-master.c
+++ b/drivers/i3c/master/svc-i3c-master.c
@@ -465,14 +465,22 @@ static int svc_i3c_master_handle_ibi(struct svc_i3c_master *master,
 	buf = slot->data;
 
 	while (SVC_I3C_MSTATUS_RXPEND(readl(master->regs + SVC_I3C_MSTATUS))  &&
-	       slot->len < SVC_I3C_FIFO_SIZE) {
+	       slot->len < dev->ibi->max_payload_len) {
 		mdatactrl = readl(master->regs + SVC_I3C_MDATACTRL);
 		count = SVC_I3C_MDATACTRL_RXCOUNT(mdatactrl);
+		count = min(count, dev->ibi->max_payload_len - slot->len);
 		readsb(master->regs + SVC_I3C_MRDATAB, buf, count);
 		slot->len += count;
 		buf += count;
 	}
 
+	/*
+	 * The device may have sent more than the requested payload. Drop the
+	 * extra bytes so they do not leak into the next transfer.
+	 */
+	if (SVC_I3C_MSTATUS_RXPEND(readl(master->regs + SVC_I3C_MSTATUS)))
+		writel(SVC_I3C_MDATACTRL_FLUSHRB, master->regs + SVC_I3C_MDATACTRL);
+
 	master->ibi.tbq_slot = slot;
 
 	return 0;