[PATCH v3 net 4/9] net: enetc: fix TOCTOU race and validate VF MAC address

[Wei Fang <wei.fang@nxp.com>]

Sashiko reported that the PF driver accepts arbitrary MAC address from
from VF mailbox messages without proper validation, creating a security
vulnerability [1].

In enetc_msg_pf_set_vf_primary_mac_addr(), the MAC address is extracted
directly from the message buffer (cmd->mac.sa_data) and programmed into
hardware via pf->ops->set_si_primary_mac() without any validity checks.
A malicious VF can configure a multicast, broadcast, or all-zero MAC
address. Therefore, a validation to check the MAC address provided by VF
is required.

However, simply checking the MAC address is not enough, because it also
has the potential TOCTOU race [2]: The code reads the MAC address from
the DMA buffer to validate it via is_valid_ether_addr(), if validation
passes, reads the same DMA buffer a second time when calling
enetc_pf_set_primary_mac_addr() to program the hardware. A malicious VF
can exploit this window by overwriting the MAC address in the DMA buffer
between the validation check and the hardware programming, bypassing the
validation entirely.

Therefore, allocate a local buffer in enetc_msg_handle_rxmsg() and copy
the message content from the DMA buffer via memcpy() before processing.
This ensures the PF operates on a stable snapshot that the VF cannot
modify.

Link: https://sashiko.dev/#/patchset/20260511080805.2052495-1-wei.fang%40nxp.com #1
Link: https://sashiko.dev/#/patchset/20260513103021.2190593-1-wei.fang%40nxp.com #2
Fixes: beb74ac878c8 ("enetc: Add vf to pf messaging support")
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
---
 .../net/ethernet/freescale/enetc/enetc_pf.c   | 39 ++++++++++++++-----
 1 file changed, 30 insertions(+), 9 deletions(-)

diff --git a/drivers/net/ethernet/freescale/enetc/enetc_pf.c b/drivers/net/ethernet/freescale/enetc/enetc_pf.c
index dea3a92c4722..09c642040892 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc_pf.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc_pf.c
@@ -478,21 +478,24 @@ static void enetc_configure_port(struct enetc_pf *pf)
 
 /* Messaging */
 static u16 enetc_msg_pf_set_vf_primary_mac_addr(struct enetc_pf *pf,
-						int vf_id)
+						int vf_id, void *msg)
 {
 	struct enetc_vf_state *vf_state = &pf->vf_state[vf_id];
-	struct enetc_msg_swbd *msg = &pf->rxmsg[vf_id];
-	struct enetc_msg_cmd_set_primary_mac *cmd;
+	struct enetc_msg_cmd_set_primary_mac *cmd = msg;
 	struct device *dev = &pf->si->pdev->dev;
-	u16 cmd_id;
+	u16 cmd_id = cmd->header.id;
 	char *addr;
 
-	cmd = (struct enetc_msg_cmd_set_primary_mac *)msg->vaddr;
-	cmd_id = cmd->header.id;
 	if (cmd_id != ENETC_MSG_CMD_MNG_ADD)
 		return ENETC_MSG_CMD_STATUS_FAIL;
 
 	addr = cmd->mac.sa_data;
+	if (!is_valid_ether_addr(addr)) {
+		dev_err_ratelimited(dev, "VF%d attempted to set invalid MAC\n",
+				    vf_id);
+		return ENETC_MSG_CMD_STATUS_FAIL;
+	}
+
 	if (vf_state->flags & ENETC_VF_FLAG_PF_SET_MAC) {
 		dev_err_ratelimited(dev,
 				    "VF%d attempted to override PF set MAC\n",
@@ -507,17 +510,33 @@ static u16 enetc_msg_pf_set_vf_primary_mac_addr(struct enetc_pf *pf,
 
 void enetc_msg_handle_rxmsg(struct enetc_pf *pf, int vf_id, u16 *status)
 {
-	struct enetc_msg_swbd *msg = &pf->rxmsg[vf_id];
+	struct enetc_msg_swbd *msg_swbd = &pf->rxmsg[vf_id];
 	struct device *dev = &pf->si->pdev->dev;
 	struct enetc_msg_cmd_header *cmd_hdr;
 	u16 cmd_type;
+	u8 *msg;
 
-	cmd_hdr = (struct enetc_msg_cmd_header *)msg->vaddr;
+	msg = kzalloc_objs(*msg, msg_swbd->size);
+	if (!msg) {
+		dev_err_ratelimited(dev,
+				    "Failed to allocate message buffer\n");
+		*status = ENETC_MSG_CMD_STATUS_FAIL;
+		return;
+	}
+
+	/* Currently, only ENETC_MSG_CMD_MNG_MAC command is supported, so
+	 * only sizeof(struct enetc_msg_cmd_set_primary_mac) bytes need to
+	 * be copied. This data already includes the cmd_type field, so it
+	 * can correctly return an error code.
+	 */
+	memcpy(msg, msg_swbd->vaddr,
+	       sizeof(struct enetc_msg_cmd_set_primary_mac));
+	cmd_hdr = (struct enetc_msg_cmd_header *)msg;
 	cmd_type = cmd_hdr->type;
 
 	switch (cmd_type) {
 	case ENETC_MSG_CMD_MNG_MAC:
-		*status = enetc_msg_pf_set_vf_primary_mac_addr(pf, vf_id);
+		*status = enetc_msg_pf_set_vf_primary_mac_addr(pf, vf_id, msg);
 		break;
 	default:
 		*status = ENETC_MSG_CMD_STATUS_FAIL;
@@ -525,6 +544,8 @@ void enetc_msg_handle_rxmsg(struct enetc_pf *pf, int vf_id, u16 *status)
 				    "command not supported (cmd_type: 0x%x)\n",
 				    cmd_type);
 	}
+
+	kfree(msg);
 }
 
 #ifdef CONFIG_PCI_IOV
-- 
2.34.1