[PATCH v2 0/2] block/blkio: fix fd leak and add more comments for the fd passing

[PATCH v2 0/2] block/blkio: fix fd leak and add more comments for the fd passing

[Stefano Garzarella]

Hanna discovered an fd leak in the error path, and a few comments to
improve in the code.

v2:
  - avoid to use `fd_supported` to track a valid fd [Hanna]

v1: https://lore.kernel.org/qemu-devel/20230801160332.122564-1-sgarzare@redhat.com/

Stefano Garzarella (2):
  block/blkio: close the fd when blkio_connect() fails
  block/blkio: add more comments on the fd passing handling

 block/blkio.c | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

-- 
2.41.0

[PATCH v2 1/2] block/blkio: close the fd when blkio_connect() fails

[Stefano Garzarella]

libblkio drivers take ownership of `fd` only after a successful
blkio_connect(), so if it fails, we are still the owners.

Fixes: cad2ccc395 ("block/blkio: use qemu_open() to support fd passing for virtio-blk")
Suggested-by: Hanna Czenczek <hreitz@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---

Notes:
    v2:
    - avoid to use `fd_supported` to track a valid fd [Hanna]

 block/blkio.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/block/blkio.c b/block/blkio.c
index 8e7ce42c79..baba2f0b67 100644
--- a/block/blkio.c
+++ b/block/blkio.c
@@ -678,7 +678,7 @@ static int blkio_virtio_blk_connect(BlockDriverState *bs, QDict *options,
     const char *path = qdict_get_try_str(options, "path");
     BDRVBlkioState *s = bs->opaque;
     bool fd_supported = false;
-    int fd, ret;
+    int fd = -1, ret;
 
     if (!path) {
         error_setg(errp, "missing 'path' option");
@@ -719,6 +719,7 @@ static int blkio_virtio_blk_connect(BlockDriverState *bs, QDict *options,
             if (ret < 0) {
                 fd_supported = false;
                 qemu_close(fd);
+                fd = -1;
             }
         }
     }
@@ -733,14 +734,18 @@ static int blkio_virtio_blk_connect(BlockDriverState *bs, QDict *options,
     }
 
     ret = blkio_connect(s->blkio);
+    if (ret < 0 && fd >= 0) {
+        /* Failed to give the FD to libblkio, close it */
+        qemu_close(fd);
+        fd = -1;
+    }
+
     /*
      * If the libblkio driver doesn't support the `fd` property, blkio_connect()
      * will fail with -EINVAL. So let's try calling blkio_connect() again by
      * directly setting `path`.
      */
     if (fd_supported && ret == -EINVAL) {
-        qemu_close(fd);
-
         /*
          * We need to clear the `fd` property we set previously by setting
          * it to -1.
-- 
2.41.0

[PATCH v2 2/2] block/blkio: add more comments on the fd passing handling

[Stefano Garzarella]

As Hanna pointed out, it is not clear in the code why qemu_open()
can fail, and why blkio_set_int("fd") is not enough to discover
the `fd` property support.

Let's fix them by adding more details in the code comments.

Suggested-by: Hanna Czenczek <hreitz@redhat.com>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 block/blkio.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/block/blkio.c b/block/blkio.c
index baba2f0b67..1dd495617c 100644
--- a/block/blkio.c
+++ b/block/blkio.c
@@ -713,6 +713,12 @@ static int blkio_virtio_blk_connect(BlockDriverState *bs, QDict *options,
          */
         fd = qemu_open(path, O_RDWR, NULL);
         if (fd < 0) {
+            /*
+             * qemu_open() can fail if the user specifies a path that is not
+             * a file or device, for example in the case of Unix Domain Socket
+             * for the virtio-blk-vhost-user driver. In such cases let's have
+             * libblkio open the path directly.
+             */
             fd_supported = false;
         } else {
             ret = blkio_set_int(s->blkio, "fd", fd);
@@ -741,9 +747,12 @@ static int blkio_virtio_blk_connect(BlockDriverState *bs, QDict *options,
     }
 
     /*
-     * If the libblkio driver doesn't support the `fd` property, blkio_connect()
-     * will fail with -EINVAL. So let's try calling blkio_connect() again by
-     * directly setting `path`.
+     * Before https://gitlab.com/libblkio/libblkio/-/merge_requests/208
+     * (libblkio <= v1.3.0), setting the `fd` property is not enough to check
+     * whether the driver supports the `fd` property or not. In that case,
+     * blkio_connect() will fail with -EINVAL.
+     * So let's try calling blkio_connect() again by directly setting `path`
+     * to cover this scenario.
      */
     if (fd_supported && ret == -EINVAL) {
         /*
-- 
2.41.0

Re: [PATCH v2 1/2] block/blkio: close the fd when blkio_connect() fails

[Hanna Czenczek]

On 03.08.23 10:28, Stefano Garzarella wrote:
> libblkio drivers take ownership of `fd` only after a successful
> blkio_connect(), so if it fails, we are still the owners.
>
> Fixes: cad2ccc395 ("block/blkio: use qemu_open() to support fd passing for virtio-blk")
> Suggested-by: Hanna Czenczek <hreitz@redhat.com>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
>
> Notes:
>      v2:
>      - avoid to use `fd_supported` to track a valid fd [Hanna]
>
>   block/blkio.c | 11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)

Thanks!

Reviewed-by: Hanna Czenczek <hreitz@redhat.com>

Re: [PATCH v2 0/2] block/blkio: fix fd leak and add more comments for the fd passing

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 709 bytes --]

On Thu, Aug 03, 2023 at 10:28:23AM +0200, Stefano Garzarella wrote:
> Hanna discovered an fd leak in the error path, and a few comments to
> improve in the code.
> 
> v2:
>   - avoid to use `fd_supported` to track a valid fd [Hanna]
> 
> v1: https://lore.kernel.org/qemu-devel/20230801160332.122564-1-sgarzare@redhat.com/
> 
> Stefano Garzarella (2):
>   block/blkio: close the fd when blkio_connect() fails
>   block/blkio: add more comments on the fd passing handling
> 
>  block/blkio.c | 26 ++++++++++++++++++++------
>  1 file changed, 20 insertions(+), 6 deletions(-)
> 
> -- 
> 2.41.0
> 

Thanks, applied to my block tree:
https://gitlab.com/stefanha/qemu/commits/block

Stefan

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]