On Thu, Jan 15, 2026 at 04:28:50PM +0800, Jianping Li wrote:
> From: Ekansh Gupta <[email protected]>
>
> fastrpc_req_munmap_impl() is called to unmap any buffer. The buffer is
> getting removed from the list after it is unmapped from DSP. This can
> create potential race conditions if any other thread removes the entry
> from list while unmap operation is ongoing. Remove the entry before
> calling unmap operation.
>
> Fixes: 2419e55e532de ("misc: fastrpc: add mmap/unmap support")
> Cc: [email protected]
> Co-developed-by: Ekansh Gupta <[email protected]>
> Signed-off-by: Ekansh Gupta <[email protected]>
> Signed-off-by: Jianping Li <[email protected]>
> ---
> drivers/misc/fastrpc.c | 28 ++++++++++++++++++++--------
> 1 file changed, 20 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index 4f12fa5a05aa..833c265add5e 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -202,6 +202,8 @@ struct fastrpc_buf {
> /* mmap support */
> struct list_head node; /* list of user requested mmaps */
> uintptr_t raddr;
> + /* Lock for buf->node */
> + spinlock_t *list_lock;
Why do you need to lock this? Isn't fl->lock enough?
> };
>
> struct fastrpc_dma_buf_attachment {
> @@ -441,6 +443,7 @@ static int __fastrpc_buf_alloc(struct fastrpc_user *fl,
> struct device *dev,
> buf->size = size;
> buf->dev = dev;
> buf->raddr = 0;
> + buf->list_lock = &fl->lock;
>
> buf->virt = dma_alloc_coherent(dev, buf->size, &buf->dma_addr,
> GFP_KERNEL);
> @@ -1865,9 +1868,6 @@ static int fastrpc_req_munmap_impl(struct fastrpc_user
> *fl, struct fastrpc_buf *
> &args[0]);
> if (!err) {
> dev_dbg(dev, "unmmap\tpt 0x%09lx OK\n", buf->raddr);
> - spin_lock(&fl->lock);
> - list_del(&buf->node);
> - spin_unlock(&fl->lock);
> fastrpc_buf_free(buf);
> } else {
> dev_err(dev, "unmmap\tpt 0x%09lx ERROR\n", buf->raddr);
> @@ -1881,6 +1881,7 @@ static int fastrpc_req_munmap(struct fastrpc_user *fl,
> char __user *argp)
> struct fastrpc_buf *buf = NULL, *iter, *b;
> struct fastrpc_req_munmap req;
> struct device *dev = fl->sctx->dev;
> + int err;
>
> if (copy_from_user(&req, argp, sizeof(req)))
> return -EFAULT;
> @@ -1888,6 +1889,7 @@ static int fastrpc_req_munmap(struct fastrpc_user *fl,
> char __user *argp)
> spin_lock(&fl->lock);
> list_for_each_entry_safe(iter, b, &fl->mmaps, node) {
> if ((iter->raddr == req.vaddrout) && (iter->size == req.size)) {
> + list_del(&iter->node);
> buf = iter;
> break;
> }
> @@ -1900,7 +1902,14 @@ static int fastrpc_req_munmap(struct fastrpc_user *fl,
> char __user *argp)
> return -EINVAL;
> }
>
> - return fastrpc_req_munmap_impl(fl, buf);
> + err = fastrpc_req_munmap_impl(fl, buf);
> + if (err) {
> + spin_lock(buf->list_lock);
> + list_add_tail(&buf->node, &fl->mmaps);
> + spin_unlock(buf->list_lock);
> + }
> +
> + return err;
> }
>
> static int fastrpc_req_mmap(struct fastrpc_user *fl, char __user *argp)
> @@ -1985,20 +1994,23 @@ static int fastrpc_req_mmap(struct fastrpc_user *fl,
> char __user *argp)
> }
> }
>
> - spin_lock(&fl->lock);
> + spin_lock(buf->list_lock);
> list_add_tail(&buf->node, &fl->mmaps);
> - spin_unlock(&fl->lock);
> + spin_unlock(buf->list_lock);
>
> if (copy_to_user((void __user *)argp, &req, sizeof(req))) {
> err = -EFAULT;
> - goto err_assign;
> + goto err_copy;
> }
>
> dev_dbg(dev, "mmap\t\tpt 0x%09lx OK [len 0x%08llx]\n",
> buf->raddr, buf->size);
>
> return 0;
> -
> +err_copy:
> + spin_lock(buf->list_lock);
> + list_del(&buf->node);
> + spin_unlock(buf->list_lock);
> err_assign:
> fastrpc_req_munmap_impl(fl, buf);
>
> --
> 2.43.0
>
--
With best wishes
Dmitry
