[PATCH] net: wwan: iosm: validate msg_head before indexing msg_ring

[liuc63]

From: Liu Chao <liuc63@xxxxxxxxxxxx>

ipc_protocol_free_msg_get() reads msg_head from shared memory and
uses it directly as an index into msg_ring[]. If the head is out
of range, the subsequent memset() writes beyond the message ring.

Validate head against IPC_MEM_MSG_ENTRIES before using it as an
index. The ring is a circular buffer, so a value outside the valid
range indicates a corrupted head pointer; report the error and fail
the allocation instead of writing out of bounds.

Fixes: 64516f633bfd ("net: iosm: protocol operations")
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Fang Xieyan <fangxy@xxxxxxxxxxxx>
Signed-off-by: Liu Chao <liuc63@xxxxxxxxxxxx>
---
 drivers/net/wwan/iosm/iosm_ipc_protocol_ops.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/wwan/iosm/iosm_ipc_protocol_ops.c b/drivers/net/wwan/iosm/iosm_ipc_protocol_ops.c
index f2f86f41fd10..004920068c45 100644
--- a/drivers/net/wwan/iosm/iosm_ipc_protocol_ops.c
+++ b/drivers/net/wwan/iosm/iosm_ipc_protocol_ops.c
@@ -14,6 +14,11 @@ ipc_protocol_free_msg_get(struct iosm_protocol *ipc_protocol, int *index)
 	u32 new_head = (head + 1) % IPC_MEM_MSG_ENTRIES;
 	union ipc_mem_msg_entry *msg;
 
+	if (head >= IPC_MEM_MSG_ENTRIES) {
+		dev_err(ipc_protocol->dev, "invalid message head %u", head);
+		return NULL;
+	}
+
 	if (new_head == le32_to_cpu(ipc_protocol->p_ap_shm->msg_tail)) {
 		dev_err(ipc_protocol->dev, "message ring is full");
 		return NULL;
-- 
2.50.1