From: Mohsin Bashir Date: Tue, 25 Nov 2025 21:17:04 +0000 (-0800) Subject: eth: fbnic: Fix counter roll-over issue X-Git-Tag: v6.18~19^2~7 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=6d66e093e0740d39a36ef742c60eec247df26f41;p=thirdparty%2Flinux.git eth: fbnic: Fix counter roll-over issue Fix a potential counter roll-over issue in fbnic_mbx_alloc_rx_msgs() when calculating descriptor slots. The issue occurs when head - tail results in a large positive value (unsigned) and the compiler interprets head - tail - 1 as a signed value. Since FBNIC_IPC_MBX_DESC_LEN is a power of two, use a masking operation, which is a common way of avoiding this problem when dealing with these sort of ring space calculations. Fixes: da3cde08209e ("eth: fbnic: Add FW communication mechanism") Signed-off-by: Mohsin Bashir Link: https://patch.msgid.link/20251125211704.3222413-1-mohsin.bashr@gmail.com Signed-off-by: Jakub Kicinski --- diff --git a/drivers/net/ethernet/meta/fbnic/fbnic_fw.c b/drivers/net/ethernet/meta/fbnic/fbnic_fw.c index c87cb9ed09e7e..fcd9912e7ad3b 100644 --- a/drivers/net/ethernet/meta/fbnic/fbnic_fw.c +++ b/drivers/net/ethernet/meta/fbnic/fbnic_fw.c @@ -201,7 +201,7 @@ static int fbnic_mbx_alloc_rx_msgs(struct fbnic_dev *fbd) return -ENODEV; /* Fill all but 1 unused descriptors in the Rx queue. */ - count = (head - tail - 1) % FBNIC_IPC_MBX_DESC_LEN; + count = (head - tail - 1) & (FBNIC_IPC_MBX_DESC_LEN - 1); while (!err && count--) { struct fbnic_tlv_msg *msg;