Re: [PATCH v4 2/9] virtiofsd: Fix breakage due to fuse_init_in size change

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Vivek Goyal (vgoyal@redhat.com) wrote:
> Kernel version 5.17 has increased the size of "struct fuse_init_in" struct.
> Previously this struct was 16 bytes and now it has been extended to
> 64 bytes in size.
> 
> Once qemu headers are updated to latest, it will expect to receive 64 byte
> size struct (for protocol version major 7 and minor > 6). But if guest is
> booting older kernel (older than 5.17), then it still sends older
> fuse_init_in of size 16 bytes. And do_init() fails. It is expecting
> 64 byte struct. And this results in mount of virtiofs failing.
> 
> Fix this by parsing 16 bytes only for now. Separate patches will be
> posted which will parse rest of the bytes and enable new functionality.
> Right now we don't support any of the new functionality, so we don't
> lose anything by not parsing bytes beyond 16.
> 
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

OK, I think we should make this 1/9 and get this in quickly; that way
bisect works.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  tools/virtiofsd/fuse_lowlevel.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/virtiofsd/fuse_lowlevel.c b/tools/virtiofsd/fuse_lowlevel.c
> index e4679c73ab..ce29a70253 100644
> --- a/tools/virtiofsd/fuse_lowlevel.c
> +++ b/tools/virtiofsd/fuse_lowlevel.c
> @@ -1880,6 +1880,7 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid,
>                      struct fuse_mbuf_iter *iter)
>  {
>      size_t compat_size = offsetof(struct fuse_init_in, max_readahead);
> +    size_t compat2_size = offsetof(struct fuse_init_in, flags) + sizeof(uint32_t);

Yeh so that sizeof() is sizeof the flags, so that's the size of the
sturcture upto and including the flags.

>      struct fuse_init_in *arg;
>      struct fuse_init_out outarg;
>      struct fuse_session *se = req->se;
> @@ -1897,7 +1898,7 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid,
>  
>      /* ...and now consume the new fields. */
>      if (arg->major == 7 && arg->minor >= 6) {
> -        if (!fuse_mbuf_iter_advance(iter, sizeof(*arg) - compat_size)) {
> +        if (!fuse_mbuf_iter_advance(iter, compat2_size - compat_size)) {
>              fuse_reply_err(req, EINVAL);
>              return;
>          }
> -- 
> 2.31.1
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK