[PATCH net 2/2] net: enetc: fix NTMP DMA use-after-free issue

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

The AI-generated review reported a potential DMA use-after-free issue
[1]. If netc_xmit_ntmp_cmd() times out and returns an error, the pending
command is not explicitly aborted, while ntmp_free_data_mem()
unconditionally frees the DMA buffer. If the buffer has already been
reallocated elsewhere, this may lead to silent memory corruption. Because
the hardware eventually processes the pending command and perform a DMA
write of the response to the physical address of the freed buffer.

To resolve this issue, this patch does the following modifications:

1. Convert cbdr->ring_lock from a spinlock to a mutex

The lock was originally a spinlock in case NTMP operations might be
invoked from atomic context. After downstream support for all NTMP
tables, no such usage has materialized. A mutex lock is now required
because the driver now needs to reclaim used BDs and release associated
DMA memory within the lock's context, while dma_free_coherent() might
sleep.

2. Introduce software command BD (struct netc_swcbd)

The hardware write-back overwrites the addr and len fields of the BD,
so the driver cannot rely on the hardware BD to free the associated DMA
memory. The driver now maintains a software shadow BD storing the DMA
buffer pointer, DMA address, and size. And netc_xmit_ntmp_cmd() only
reclaims older BDs when the number of used BDs reaches
NETC_CBDR_CLEAN_WORK (16). The software BD enables correct DMA memory
release. With this, struct ntmp_dma_buf and ntmp_free_data_mem() are no
longer needed and are removed.

These changes eliminate the DMA use-after-free condition and ensure safe
and consistent BD reclamation and DMA buffer lifecycle management.

Fixes: 4701073c3deb ("net: enetc: add initial netc-lib driver to support NTMP")
Link: https://lore.kernel.org/netdev/20260403011729.1795413-1-kuba@kernel.org/ # [1]
Signed-off-by: Wei Fang <wei.fang@nxp.com>
---
 drivers/net/ethernet/freescale/enetc/ntmp.c   | 158 ++++++++++--------
 .../ethernet/freescale/enetc/ntmp_private.h   |   8 +-
 include/linux/fsl/ntmp.h                      |   9 +-
 3 files changed, 93 insertions(+), 82 deletions(-)

diff --git a/drivers/net/ethernet/freescale/enetc/ntmp.c b/drivers/net/ethernet/freescale/enetc/ntmp.c
index 1b1ff0446d0a..3efc65443113 100644
--- a/drivers/net/ethernet/freescale/enetc/ntmp.c
+++ b/drivers/net/ethernet/freescale/enetc/ntmp.c
@@ -7,6 +7,7 @@
 #include <linux/dma-mapping.h>
 #include <linux/fsl/netc_global.h>
 #include <linux/iopoll.h>
+#include <linux/vmalloc.h>
 
 #include "ntmp_private.h"
 
@@ -42,6 +43,12 @@ int ntmp_init_cbdr(struct netc_cbdr *cbdr, struct device *dev,
 	if (!cbdr->addr_base)
 		return -ENOMEM;
 
+	cbdr->swcbd = vcalloc(cbd_num, sizeof(struct netc_swcbd));
+	if (!cbdr->swcbd) {
+		dma_free_coherent(dev, size, cbdr->addr_base, cbdr->dma_base);
+		return -ENOMEM;
+	}
+
 	cbdr->dma_size = size;
 	cbdr->bd_num = cbd_num;
 	cbdr->regs = *regs;
@@ -52,7 +59,7 @@ int ntmp_init_cbdr(struct netc_cbdr *cbdr, struct device *dev,
 	cbdr->addr_base_align = PTR_ALIGN(cbdr->addr_base,
 					  NTMP_BASE_ADDR_ALIGN);
 
-	spin_lock_init(&cbdr->ring_lock);
+	mutex_init(&cbdr->ring_lock);
 
 	cbdr->next_to_use = netc_read(cbdr->regs.pir);
 	cbdr->next_to_clean = netc_read(cbdr->regs.cir) & NETC_CBDRCIR_INDEX;
@@ -71,10 +78,25 @@ int ntmp_init_cbdr(struct netc_cbdr *cbdr, struct device *dev,
 }
 EXPORT_SYMBOL_GPL(ntmp_init_cbdr);
 
+static void ntmp_free_data_mem(struct device *dev, struct netc_swcbd *swcbd)
+{
+	dma_free_coherent(dev, swcbd->size + NTMP_DATA_ADDR_ALIGN,
+			  swcbd->buf, swcbd->dma);
+}
+
 void ntmp_free_cbdr(struct netc_cbdr *cbdr)
 {
 	/* Disable the Control BD Ring */
 	netc_write(cbdr->regs.mr, 0);
+
+	for (int i = 0; i < cbdr->bd_num; i++) {
+		struct netc_swcbd *swcbd = &cbdr->swcbd[i];
+
+		if (swcbd->dma)
+			ntmp_free_data_mem(cbdr->dev, swcbd);
+	}
+
+	vfree(cbdr->swcbd);
 	dma_free_coherent(cbdr->dev, cbdr->dma_size, cbdr->addr_base,
 			  cbdr->dma_base);
 	memset(cbdr, 0, sizeof(*cbdr));
@@ -94,24 +116,28 @@ static union netc_cbd *ntmp_get_cbd(struct netc_cbdr *cbdr, int index)
 
 static void ntmp_clean_cbdr(struct netc_cbdr *cbdr)
 {
-	union netc_cbd *cbd;
-	int i;
+	int i = cbdr->next_to_clean;
 
-	i = cbdr->next_to_clean;
 	while ((netc_read(cbdr->regs.cir) & NETC_CBDRCIR_INDEX) != i) {
-		cbd = ntmp_get_cbd(cbdr, i);
+		union netc_cbd *cbd = ntmp_get_cbd(cbdr, i);
+		struct netc_swcbd *swcbd = &cbdr->swcbd[i];
+
+		ntmp_free_data_mem(cbdr->dev, swcbd);
+		memset(swcbd, 0, sizeof(*swcbd));
 		memset(cbd, 0, sizeof(*cbd));
 		i = (i + 1) % cbdr->bd_num;
 	}
 
+	dma_wmb();
 	cbdr->next_to_clean = i;
 }
 
-static int netc_xmit_ntmp_cmd(struct ntmp_user *user, union netc_cbd *cbd)
+static int netc_xmit_ntmp_cmd(struct ntmp_user *user, union netc_cbd *cbd,
+			      struct netc_swcbd *swcbd)
 {
 	union netc_cbd *cur_cbd;
 	struct netc_cbdr *cbdr;
-	int i, err;
+	int i, err, used_bds;
 	u16 status;
 	u32 val;
 
@@ -120,14 +146,21 @@ static int netc_xmit_ntmp_cmd(struct ntmp_user *user, union netc_cbd *cbd)
 	 */
 	cbdr = &user->ring[0];
 
-	spin_lock_bh(&cbdr->ring_lock);
+	mutex_lock(&cbdr->ring_lock);
 
-	if (unlikely(!ntmp_get_free_cbd_num(cbdr)))
+	used_bds = cbdr->bd_num - ntmp_get_free_cbd_num(cbdr);
+	if (unlikely(used_bds >= NETC_CBDR_CLEAN_WORK)) {
 		ntmp_clean_cbdr(cbdr);
+		if (unlikely(!ntmp_get_free_cbd_num(cbdr))) {
+			err = -EBUSY;
+			goto cbdr_unlock;
+		}
+	}
 
 	i = cbdr->next_to_use;
 	cur_cbd = ntmp_get_cbd(cbdr, i);
 	*cur_cbd = *cbd;
+	cbdr->swcbd[i] = *swcbd;
 	dma_wmb();
 
 	/* Update producer index of both software and hardware */
@@ -135,10 +168,9 @@ static int netc_xmit_ntmp_cmd(struct ntmp_user *user, union netc_cbd *cbd)
 	cbdr->next_to_use = i;
 	netc_write(cbdr->regs.pir, i);
 
-	err = read_poll_timeout_atomic(netc_read, val,
-				       (val & NETC_CBDRCIR_INDEX) == i,
-				       NETC_CBDR_DELAY_US, NETC_CBDR_TIMEOUT,
-				       true, cbdr->regs.cir);
+	err = read_poll_timeout(netc_read, val, (val & NETC_CBDRCIR_INDEX) == i,
+				NETC_CBDR_DELAY_US, NETC_CBDR_TIMEOUT,
+				true, cbdr->regs.cir);
 	if (unlikely(err))
 		goto cbdr_unlock;
 
@@ -155,36 +187,28 @@ static int netc_xmit_ntmp_cmd(struct ntmp_user *user, union netc_cbd *cbd)
 		dev_err(user->dev, "Command BD error: 0x%04x\n", status);
 	}
 
-	ntmp_clean_cbdr(cbdr);
-	dma_wmb();
-
 cbdr_unlock:
-	spin_unlock_bh(&cbdr->ring_lock);
+	mutex_unlock(&cbdr->ring_lock);
 
 	return err;
 }
 
-static int ntmp_alloc_data_mem(struct ntmp_dma_buf *data, void **buf_align)
+static int ntmp_alloc_data_mem(struct device *dev, struct netc_swcbd *swcbd,
+			       void **buf_align)
 {
 	void *buf;
 
-	buf = dma_alloc_coherent(data->dev, data->size + NTMP_DATA_ADDR_ALIGN,
-				 &data->dma, GFP_KERNEL);
+	buf = dma_alloc_coherent(dev, swcbd->size + NTMP_DATA_ADDR_ALIGN,
+				 &swcbd->dma, GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
 
-	data->buf = buf;
+	swcbd->buf = buf;
 	*buf_align = PTR_ALIGN(buf, NTMP_DATA_ADDR_ALIGN);
 
 	return 0;
 }
 
-static void ntmp_free_data_mem(struct ntmp_dma_buf *data)
-{
-	dma_free_coherent(data->dev, data->size + NTMP_DATA_ADDR_ALIGN,
-			  data->buf, data->dma);
-}
-
 static void ntmp_fill_request_hdr(union netc_cbd *cbd, dma_addr_t dma,
 				  int len, int table_id, int cmd,
 				  int access_method)
@@ -235,37 +259,36 @@ static int ntmp_delete_entry_by_id(struct ntmp_user *user, int tbl_id,
 				   u8 tbl_ver, u32 entry_id, u32 req_len,
 				   u32 resp_len)
 {
-	struct ntmp_dma_buf data = {
-		.dev = user->dev,
+	struct netc_swcbd swcbd = {
 		.size = max(req_len, resp_len),
 	};
 	struct ntmp_req_by_eid *req;
 	union netc_cbd cbd;
 	int err;
 
-	err = ntmp_alloc_data_mem(&data, (void **)&req);
+	err = ntmp_alloc_data_mem(user->dev, &swcbd, (void **)&req);
 	if (err)
 		return err;
 
 	ntmp_fill_crd_eid(req, tbl_ver, 0, 0, entry_id);
-	ntmp_fill_request_hdr(&cbd, data.dma, NTMP_LEN(req_len, resp_len),
+	ntmp_fill_request_hdr(&cbd, swcbd.dma, NTMP_LEN(req_len, resp_len),
 			      tbl_id, NTMP_CMD_DELETE, NTMP_AM_ENTRY_ID);
 
-	err = netc_xmit_ntmp_cmd(user, &cbd);
+	err = netc_xmit_ntmp_cmd(user, &cbd, &swcbd);
 	if (err)
 		dev_err(user->dev,
 			"Failed to delete entry 0x%x of %s, err: %pe",
 			entry_id, ntmp_table_name(tbl_id), ERR_PTR(err));
 
-	ntmp_free_data_mem(&data);
-
 	return err;
 }
 
 static int ntmp_query_entry_by_id(struct ntmp_user *user, int tbl_id,
-				  u32 len, struct ntmp_req_by_eid *req,
-				  dma_addr_t dma, bool compare_eid)
+				  struct ntmp_req_by_eid *req,
+				  struct netc_swcbd *swcbd,
+				  bool compare_eid)
 {
+	u32 len = NTMP_LEN(sizeof(*req), swcbd->size);
 	struct ntmp_cmn_resp_query *resp;
 	int cmd = NTMP_CMD_QUERY;
 	union netc_cbd cbd;
@@ -277,8 +300,9 @@ static int ntmp_query_entry_by_id(struct ntmp_user *user, int tbl_id,
 		cmd = NTMP_CMD_QU;
 
 	/* Request header */
-	ntmp_fill_request_hdr(&cbd, dma, len, tbl_id, cmd, NTMP_AM_ENTRY_ID);
-	err = netc_xmit_ntmp_cmd(user, &cbd);
+	ntmp_fill_request_hdr(&cbd, swcbd->dma, len, tbl_id, cmd,
+			      NTMP_AM_ENTRY_ID);
+	err = netc_xmit_ntmp_cmd(user, &cbd, swcbd);
 	if (err) {
 		dev_err(user->dev,
 			"Failed to query entry 0x%x of %s, err: %pe\n",
@@ -306,15 +330,14 @@ static int ntmp_query_entry_by_id(struct ntmp_user *user, int tbl_id,
 int ntmp_maft_add_entry(struct ntmp_user *user, u32 entry_id,
 			struct maft_entry_data *maft)
 {
-	struct ntmp_dma_buf data = {
-		.dev = user->dev,
+	struct netc_swcbd swcbd = {
 		.size = sizeof(struct maft_req_add),
 	};
 	struct maft_req_add *req;
 	union netc_cbd cbd;
 	int err;
 
-	err = ntmp_alloc_data_mem(&data, (void **)&req);
+	err = ntmp_alloc_data_mem(user->dev, &swcbd, (void **)&req);
 	if (err)
 		return err;
 
@@ -323,15 +346,13 @@ int ntmp_maft_add_entry(struct ntmp_user *user, u32 entry_id,
 	req->keye = maft->keye;
 	req->cfge = maft->cfge;
 
-	ntmp_fill_request_hdr(&cbd, data.dma, NTMP_LEN(data.size, 0),
+	ntmp_fill_request_hdr(&cbd, swcbd.dma, NTMP_LEN(swcbd.size, 0),
 			      NTMP_MAFT_ID, NTMP_CMD_ADD, NTMP_AM_ENTRY_ID);
-	err = netc_xmit_ntmp_cmd(user, &cbd);
+	err = netc_xmit_ntmp_cmd(user, &cbd, &swcbd);
 	if (err)
 		dev_err(user->dev, "Failed to add MAFT entry 0x%x, err: %pe\n",
 			entry_id, ERR_PTR(err));
 
-	ntmp_free_data_mem(&data);
-
 	return err;
 }
 EXPORT_SYMBOL_GPL(ntmp_maft_add_entry);
@@ -339,33 +360,27 @@ EXPORT_SYMBOL_GPL(ntmp_maft_add_entry);
 int ntmp_maft_query_entry(struct ntmp_user *user, u32 entry_id,
 			  struct maft_entry_data *maft)
 {
-	struct ntmp_dma_buf data = {
-		.dev = user->dev,
+	struct netc_swcbd swcbd = {
 		.size = sizeof(struct maft_resp_query),
 	};
 	struct maft_resp_query *resp;
 	struct ntmp_req_by_eid *req;
 	int err;
 
-	err = ntmp_alloc_data_mem(&data, (void **)&req);
+	err = ntmp_alloc_data_mem(user->dev, &swcbd, (void **)&req);
 	if (err)
 		return err;
 
 	ntmp_fill_crd_eid(req, user->tbl.maft_ver, 0, 0, entry_id);
-	err = ntmp_query_entry_by_id(user, NTMP_MAFT_ID,
-				     NTMP_LEN(sizeof(*req), data.size),
-				     req, data.dma, true);
+	err = ntmp_query_entry_by_id(user, NTMP_MAFT_ID, req, &swcbd, true);
 	if (err)
-		goto end;
+		return err;
 
 	resp = (struct maft_resp_query *)req;
 	maft->keye = resp->keye;
 	maft->cfge = resp->cfge;
 
-end:
-	ntmp_free_data_mem(&data);
-
-	return err;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(ntmp_maft_query_entry);
 
@@ -379,8 +394,8 @@ EXPORT_SYMBOL_GPL(ntmp_maft_delete_entry);
 int ntmp_rsst_update_entry(struct ntmp_user *user, const u32 *table,
 			   int count)
 {
-	struct ntmp_dma_buf data = {.dev = user->dev};
 	struct rsst_req_update *req;
+	struct netc_swcbd swcbd;
 	union netc_cbd cbd;
 	int err, i;
 
@@ -388,8 +403,8 @@ int ntmp_rsst_update_entry(struct ntmp_user *user, const u32 *table,
 		/* HW only takes in a full 64 entry table */
 		return -EINVAL;
 
-	data.size = struct_size(req, groups, count);
-	err = ntmp_alloc_data_mem(&data, (void **)&req);
+	swcbd.size = struct_size(req, groups, count);
+	err = ntmp_alloc_data_mem(user->dev, &swcbd, (void **)&req);
 	if (err)
 		return err;
 
@@ -399,24 +414,22 @@ int ntmp_rsst_update_entry(struct ntmp_user *user, const u32 *table,
 	for (i = 0; i < count; i++)
 		req->groups[i] = (u8)(table[i]);
 
-	ntmp_fill_request_hdr(&cbd, data.dma, NTMP_LEN(data.size, 0),
+	ntmp_fill_request_hdr(&cbd, swcbd.dma, NTMP_LEN(swcbd.size, 0),
 			      NTMP_RSST_ID, NTMP_CMD_UPDATE, NTMP_AM_ENTRY_ID);
 
-	err = netc_xmit_ntmp_cmd(user, &cbd);
+	err = netc_xmit_ntmp_cmd(user, &cbd, &swcbd);
 	if (err)
 		dev_err(user->dev, "Failed to update RSST entry, err: %pe\n",
 			ERR_PTR(err));
 
-	ntmp_free_data_mem(&data);
-
 	return err;
 }
 EXPORT_SYMBOL_GPL(ntmp_rsst_update_entry);
 
 int ntmp_rsst_query_entry(struct ntmp_user *user, u32 *table, int count)
 {
-	struct ntmp_dma_buf data = {.dev = user->dev};
 	struct ntmp_req_by_eid *req;
+	struct netc_swcbd swcbd;
 	union netc_cbd cbd;
 	int err, i;
 	u8 *group;
@@ -425,21 +438,21 @@ int ntmp_rsst_query_entry(struct ntmp_user *user, u32 *table, int count)
 		/* HW only takes in a full 64 entry table */
 		return -EINVAL;
 
-	data.size = NTMP_ENTRY_ID_SIZE + RSST_STSE_DATA_SIZE(count) +
-		    RSST_CFGE_DATA_SIZE(count);
-	err = ntmp_alloc_data_mem(&data, (void **)&req);
+	swcbd.size = NTMP_ENTRY_ID_SIZE + RSST_STSE_DATA_SIZE(count) +
+		     RSST_CFGE_DATA_SIZE(count);
+	err = ntmp_alloc_data_mem(user->dev, &swcbd, (void **)&req);
 	if (err)
 		return err;
 
 	/* Set the request data buffer */
 	ntmp_fill_crd_eid(req, user->tbl.rsst_ver, 0, 0, 0);
-	ntmp_fill_request_hdr(&cbd, data.dma, NTMP_LEN(sizeof(*req), data.size),
+	ntmp_fill_request_hdr(&cbd, swcbd.dma, NTMP_LEN(sizeof(*req), swcbd.size),
 			      NTMP_RSST_ID, NTMP_CMD_QUERY, NTMP_AM_ENTRY_ID);
-	err = netc_xmit_ntmp_cmd(user, &cbd);
+	err = netc_xmit_ntmp_cmd(user, &cbd, &swcbd);
 	if (err) {
 		dev_err(user->dev, "Failed to query RSST entry, err: %pe\n",
 			ERR_PTR(err));
-		goto end;
+		return err;
 	}
 
 	group = (u8 *)req;
@@ -447,10 +460,7 @@ int ntmp_rsst_query_entry(struct ntmp_user *user, u32 *table, int count)
 	for (i = 0; i < count; i++)
 		table[i] = group[i];
 
-end:
-	ntmp_free_data_mem(&data);
-
-	return err;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(ntmp_rsst_query_entry);
 
diff --git a/drivers/net/ethernet/freescale/enetc/ntmp_private.h b/drivers/net/ethernet/freescale/enetc/ntmp_private.h
index 7a53db8740db..5ae6f8b92700 100644
--- a/drivers/net/ethernet/freescale/enetc/ntmp_private.h
+++ b/drivers/net/ethernet/freescale/enetc/ntmp_private.h
@@ -13,6 +13,7 @@
 #define NTMP_EID_REQ_LEN	8
 #define NETC_CBDR_BD_NUM	256
 #define NETC_CBDRCIR_INDEX	GENMASK(9, 0)
+#define NETC_CBDR_CLEAN_WORK	16
 
 union netc_cbd {
 	struct {
@@ -55,13 +56,6 @@ union netc_cbd {
 	} resp_hdr; /* NTMP Response Message Header Format */
 };
 
-struct ntmp_dma_buf {
-	struct device *dev;
-	size_t size;
-	void *buf;
-	dma_addr_t dma;
-};
-
 struct ntmp_cmn_req_data {
 	__le16 update_act;
 	u8 dbg_opt;
diff --git a/include/linux/fsl/ntmp.h b/include/linux/fsl/ntmp.h
index 916dc4fe7de3..83a449b4d6ec 100644
--- a/include/linux/fsl/ntmp.h
+++ b/include/linux/fsl/ntmp.h
@@ -31,6 +31,12 @@ struct netc_tbl_vers {
 	u8 rsst_ver;
 };
 
+struct netc_swcbd {
+	void *buf;
+	dma_addr_t dma;
+	size_t size;
+};
+
 struct netc_cbdr {
 	struct device *dev;
 	struct netc_cbdr_regs regs;
@@ -44,9 +50,10 @@ struct netc_cbdr {
 	void *addr_base_align;
 	dma_addr_t dma_base;
 	dma_addr_t dma_base_align;
+	struct netc_swcbd *swcbd;
 
 	/* Serialize the order of command BD ring */
-	spinlock_t ring_lock;
+	struct mutex ring_lock;
 };
 
 struct ntmp_user {
-- 
2.34.1