FROMLIST: misc: fastrpc: fix UAF and kernel panic during cleanup on process abort

When a userspace FastRPC client is abruptly terminated, FastRPC
cleanup paths can race with device and session teardown.

This results in kernel panics in different release paths:
- fastrpc_release() when using remote heap, originating from
  fastrpc_buf_free()
- fastrpc_device_release() when using system heap, originating from
  fastrpc_free_map()

In addition, fastrpc_map_put() may trigger refcount use-after-free
due to concurrent cleanup without proper synchronization.

The root cause is that buffer and map cleanup paths may access map
and buf resources after the associated device or session has
already been released.

Fix this by:
- Introducing mutex protection for map and buf lifetime
- Serializing buffer and map cleanup against device teardown
- Skipping buffer and map operations when the device is already gone

These changes ensure cleanup paths are safe against unexpected
process aborts and prevent use-after-free and kernel panic scenarios.

Link: https://lore.kernel.org/all/20260427105310.4056-1-jianping.li@oss.qualcomm.com/
Fixes: c68cfb7 ("misc: fastrpc: Add support for context Invoke method")
Cc: stable@kernel.org
Signed-off-by: Jianping Li <jianping.li@oss.qualcomm.com>

Author: Jianping-Li

drivers/misc/fastrpc.c

@@ -271,6 +271,8 @@ struct fastrpc_session_ctx {
 	int sid;
 	bool used;
 	bool valid;
+	bool allocated;
+	struct mutex mutex;
 };
 
 struct fastrpc_soc_data {
@@ -355,9 +357,14 @@ static inline u64 fastrpc_sid_offset(struct fastrpc_channel_ctx *cctx,
 static void fastrpc_free_map(struct kref *ref)
 {
 	struct fastrpc_map *map;
+	struct fastrpc_user *fl;
 
 	map = container_of(ref, struct fastrpc_map, refcount);
 
+	fl = map->fl;
+	if (!fl)
+		return;
+
 	if (map->table) {
 		if (map->attr & FASTRPC_ATTR_SECUREMAP) {
 			struct qcom_scm_vmperm perm;
@@ -376,10 +383,16 @@ static void fastrpc_free_map(struct kref *ref)
 				return;
 			}
 		}
+		mutex_lock(&fl->sctx->mutex);
+		if (!fl->sctx->dev) {
+			mutex_unlock(&fl->sctx->mutex);
+			return;
+		}
 		dma_buf_unmap_attachment_unlocked(map->attach, map->table,
 						  DMA_BIDIRECTIONAL);
 		dma_buf_detach(map->buf, map->attach);
 		dma_buf_put(map->buf);
+		mutex_unlock(&fl->sctx->mutex);
 	}
 
 	if (map->fl) {
@@ -439,9 +452,18 @@ static void fastrpc_buf_free(struct fastrpc_buf *buf)
 	if (!buf)
 		return;
 
-	dma_free_coherent(buf->dev, buf->size, buf->virt,
-			  fastrpc_ipa_to_dma_addr(buf->fl->cctx, buf->dma_addr));
-	kfree(buf);
+	struct fastrpc_user *fl = buf->fl;
+
+	if (!fl)
+		return;
+	mutex_lock(&fl->sctx->mutex);
+	if (fl->sctx->dev) {
+		dma_free_coherent(buf->dev, buf->size, buf->virt,
+				  fastrpc_ipa_to_dma_addr(buf->fl->cctx,
+							  buf->dma_addr));
+		kfree(buf);
+	}
+	mutex_unlock(&fl->sctx->mutex);
 }
 
 static int __fastrpc_buf_alloc(struct fastrpc_user *fl, struct device *dev,
@@ -464,8 +486,11 @@ static int __fastrpc_buf_alloc(struct fastrpc_user *fl, struct device *dev,
 	buf->dev = dev;
 	buf->raddr = 0;
 
-	buf->virt = dma_alloc_coherent(dev, buf->size, &buf->dma_addr,
-				       GFP_KERNEL);
+	mutex_lock(&fl->sctx->mutex);
+	if (fl->sctx->dev)
+		buf->virt = dma_alloc_coherent(dev, buf->size, &buf->dma_addr,
+					       GFP_KERNEL);
+	mutex_unlock(&fl->sctx->mutex);
 	if (!buf->virt) {
 		mutex_destroy(&buf->lock);
 		kfree(buf);
@@ -508,6 +533,10 @@ static void fastrpc_channel_ctx_free(struct kref *ref)
 	struct fastrpc_channel_ctx *cctx;
 
 	cctx = container_of(ref, struct fastrpc_channel_ctx, refcount);
+	for (int i = 0; i < FASTRPC_MAX_SESSIONS; i++) {
+		if (cctx->session[i].allocated)
+			mutex_destroy(&cctx->session[i].mutex);
+	}
 
 	kfree(cctx);
 }
@@ -850,19 +879,29 @@ static int fastrpc_map_attach(struct fastrpc_user *fl, int fd,
 		goto get_err;
 	}
 
+	mutex_lock(&fl->sctx->mutex);
+	if (!fl->sctx->dev) {
+		err = -ENODEV;
+		mutex_unlock(&fl->sctx->mutex);
+		goto attach_err;
+	}
+
 	map->attach = dma_buf_attach(map->buf, sess->dev);
 	if (IS_ERR(map->attach)) {
 		dev_err(sess->dev, "Failed to attach dmabuf\n");
 		err = PTR_ERR(map->attach);
+		mutex_unlock(&fl->sctx->mutex);
 		goto attach_err;
 	}
 
 	table = dma_buf_map_attachment_unlocked(map->attach, DMA_BIDIRECTIONAL);
 	if (IS_ERR(table)) {
 		err = PTR_ERR(table);
+		mutex_unlock(&fl->sctx->mutex);
 		goto map_err;
 	}
 	map->table = table;
+	mutex_unlock(&fl->sctx->mutex);
 
 	if (attr & FASTRPC_ATTR_SECUREMAP)
 		map->dma_addr = sg_phys(map->table->sgl);
@@ -2350,6 +2389,8 @@ static int fastrpc_cb_probe(struct platform_device *pdev)
 	sess->used = false;
 	sess->valid = true;
 	sess->dev = dev;
+	mutex_init(&sess->mutex);
+	sess->allocated = true;
 	dev_set_drvdata(dev, sess);
 
 	if (cctx->domain_id == CDSP_DOMAIN_ID)
@@ -2366,6 +2407,8 @@ static int fastrpc_cb_probe(struct platform_device *pdev)
 				break;
 			dup_sess = &cctx->session[cctx->sesscount++];
 			memcpy(dup_sess, sess, sizeof(*dup_sess));
+			mutex_init(&dup_sess->mutex);
+			dup_sess->allocated = true;
 		}
 	}
 	spin_unlock_irqrestore(&cctx->lock, flags);
@@ -2388,6 +2431,11 @@ static void fastrpc_cb_remove(struct platform_device *pdev)
 	spin_lock_irqsave(&cctx->lock, flags);
 	for (i = 0; i < FASTRPC_MAX_SESSIONS; i++) {
 		if (cctx->session[i].sid == sess->sid) {
+			spin_unlock_irqrestore(&cctx->lock, flags);
+			mutex_lock(&cctx->session[i].mutex);
+			cctx->session[i].dev = NULL;
+			mutex_unlock(&cctx->session[i].mutex);
+			spin_lock_irqsave(&cctx->lock, flags);
 			cctx->session[i].valid = false;
 			cctx->sesscount--;
 		}