misc: fastrpc: possible double-free of cctx->remote_heap

fastrpc_init_create_static_process() may free cctx->remote_heap on the
err_map path but does not clear the pointer. Later, fastrpc_rpmsg_remove()
frees cctx->remote_heap again if it is non-NULL, which can lead to a
double-free if the INIT_CREATE_STATIC ioctl hits the error path and the rpmsg
device is subsequently removed/unbound.
Clear cctx->remote_heap after freeing it in the error path to prevent the
later cleanup from freeing it again.

This issue was found by an in-house analysis workflow that extracts AST-based
information and runs static checks, with LLM assistance for triage, and was
confirmed by manual code review.
No hardware testing was performed.

Fixes: 0871561055 ("misc: fastrpc: Add support for audiopd")
Cc: stable@vger.kernel.org # 6.2+
Signed-off-by: Xingjing Deng <xjdeng@buaa.edu.cn>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Link: https://patch.msgid.link/20260129234140.410983-1-xjdeng@buaa.edu.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/fastrpc.c

@@ -1401,6 +1401,7 @@ err_invoke:
 	}
 err_map:
 	fastrpc_buf_free(fl->cctx->remote_heap);
+	fl->cctx->remote_heap = NULL;
 err_name:
 	kfree(name);
 err: