[PATCH] [PATCH v2] virtiofs: Strengthen FUSE protocol validation for server responses

[Li Wang]

1. We should not trust the length value provided by the server;
2. Only replies have an out header/argbuf data to parse;
3. Some minor refinements for performance and log throttling.

Signed-off-by: Li Wang <liw...@kylinos.cn>
---
 fs/fuse/virtio_fs.c | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
index 2f7485ffac52..c3f7f472f517 100644
--- a/fs/fuse/virtio_fs.c
+++ b/fs/fuse/virtio_fs.c
@@ -759,23 +759,31 @@ static void copy_args_from_argbuf(struct fuse_args *args, 
struct fuse_req *req)
 }
 
 /* Verify that the server properly follows the FUSE protocol */
-static bool virtio_fs_verify_response(struct fuse_req *req, unsigned int len)
+static bool virtio_fs_verify_response(struct fuse_req *req)
 {
+       unsigned int num_out, cap;
+       struct fuse_args *args;
        struct fuse_out_header *oh = &req->out.h;
 
-       if (len < sizeof(*oh)) {
-               pr_warn("virtio-fs: response too short (%u)\n", len);
+       if (!test_bit(FR_ISREPLY, &req->flags))
                return false;
-       }
-       if (oh->len != len) {
-               pr_warn("virtio-fs: oh.len mismatch (%u != %u)\n", oh->len, 
len);
+       if (unlikely(oh->unique != req->in.h.unique)) {
+               pr_warn_ratelimited("virtio-fs: bad reply unique %llu (expected 
%llu)\n",
+                                       oh->unique, req->in.h.unique);
                return false;
        }
-       if (oh->unique != req->in.h.unique) {
-               pr_warn("virtio-fs: oh.unique mismatch (%llu != %llu)\n",
-                       oh->unique, req->in.h.unique);
+       args = req->args;
+       num_out = args->out_numargs - args->out_pages;
+       cap = sizeof(req->out.h);
+       cap += fuse_len_args(num_out, args->out_args);
+       if (args->out_pages)
+               cap += args->out_args[args->out_numargs - 1].size;
+       if (unlikely(oh->len < sizeof(*oh) || oh->len > cap)) {
+               pr_warn_ratelimited("virtio-fs: bad reply len %u (cap %u)\n",
+                                       oh->len, cap);
                return false;
        }
+
        return true;
 }
 
@@ -841,7 +849,7 @@ static void virtio_fs_requests_done_work(struct work_struct 
*work)
                virtqueue_disable_cb(vq);
 
                while ((req = virtqueue_get_buf(vq, &len)) != NULL) {
-                       if (!virtio_fs_verify_response(req, len)) {
+                       if (test_bit(FR_ISREPLY, &req->flags) && 
!virtio_fs_verify_response(req)) {
                                req->out.h.error = -EIO;
                                req->out.h.len = sizeof(struct fuse_out_header);
                        }
-- 
2.34.1