* Greg Kurz (gr...@kaod.org) wrote:
> A well behaved FUSE client uses FUSE_CREATE to create files. It isn't
> supposed to pass O_CREAT along a FUSE_OPEN request, as documented in
> the "fuse_lowlevel.h" header :
>
> /**
> * Open a file
> *
> * Open flags are available in fi->flags. The following rules
> * apply.
> *
> * - Creation (O_CREAT, O_EXCL, O_NOCTTY) flags will be
> * filtered out / handled by the kernel.
>
> But if the client happens to do it anyway, the server ends up passing
> this flag to open() without the mandatory mode_t 4th argument. Since
> open() is a variadic function, glibc will happily pass whatever it
> finds on the stack to the syscall. If this file is compiled with
> -D_FORTIFY_SOURCE=2, glibc will even detect that and abort:
>
> *** invalid openat64 call: O_CREAT or O_TMPFILE without mode ***: terminated
>
> Specifying O_CREAT with FUSE_OPEN is a protocol violation. Check this
> in do_open(), print out a message and return an error to the client,
> EINVAL like we already do when fuse_mbuf_iter_advance() fails.
>
> The FUSE filesystem doesn't currently support O_TMPFILE, but the very
> same would happen if O_TMPFILE was passed in a FUSE_OPEN request. Check
> that as well.
>
> Signed-off-by: Greg Kurz <gr...@kaod.org>
Reviewed-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> ---
>
> v2:
> - do the check in core FUSE code instead of passthrough_ll (libfuse folks)
>
>
> tools/virtiofsd/fuse_lowlevel.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/tools/virtiofsd/fuse_lowlevel.c b/tools/virtiofsd/fuse_lowlevel.c
> index 7fe2cef1eb3b..3d725bcba2ca 100644
> --- a/tools/virtiofsd/fuse_lowlevel.c
> +++ b/tools/virtiofsd/fuse_lowlevel.c
> @@ -1084,6 +1084,12 @@ static void do_open(fuse_req_t req, fuse_ino_t nodeid,
> return;
> }
>
> + /* File creation is handled by do_create() or do_mknod() */
> + if (arg->flags & (O_CREAT | O_TMPFILE)) {
> + fuse_reply_err(req, EINVAL);
> + return;
> + }
> +
> memset(&fi, 0, sizeof(fi));
> fi.flags = arg->flags;
> fi.kill_priv = arg->open_flags & FUSE_OPEN_KILL_SUIDGID;
> --
> 2.31.1
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
