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Re: [PATCH] virtiofsd: Don't allow file creation with FUSE_OPEN
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [PATCH] virtiofsd: Don't allow file creation with FUSE_OPEN |
Date: |
Thu, 17 Jun 2021 15:29:12 +0100 |
User-agent: |
Mutt/2.0.7 (2021-05-04) |
* Greg Kurz (groug@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 it does anyway, virtiofsd crashes with:
>
> *** invalid openat64 call: O_CREAT or O_TMPFILE without mode ***: terminated
>
> This is because virtiofsd ends up passing this flag to openat() without
> passing a mode_t 4th argument which is mandatory with O_CREAT, and glibc
> aborts.
>
> The offending path is:
>
> lo_open()
> lo_do_open()
> lo_inode_open()
>
> Other callers of lo_inode_open() only pass O_RDWR and lo_create()
> passes a valid fd to lo_do_open() which thus doesn't even call
> lo_inode_open() in this case.
>
> Specifying O_CREAT with FUSE_OPEN is a protocol violation. Check this
> in lo_open() and return an error to the client : EINVAL since this is
> already what glibc returns with other illegal flag combinations.
>
> 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 <groug@kaod.org>
That seems reasonable, so
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
should you also send a corresponding patch for libfuse's example code
we're based on?
Dave
> ---
> tools/virtiofsd/passthrough_ll.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/tools/virtiofsd/passthrough_ll.c
> b/tools/virtiofsd/passthrough_ll.c
> index 49c21fd85570..14f62133131c 100644
> --- a/tools/virtiofsd/passthrough_ll.c
> +++ b/tools/virtiofsd/passthrough_ll.c
> @@ -2145,6 +2145,12 @@ static void lo_open(fuse_req_t req, fuse_ino_t ino,
> struct fuse_file_info *fi)
> return;
> }
>
> + /* File creation is handled by lo_create() */
> + if (fi->flags & (O_CREAT | O_TMPFILE)) {
> + fuse_reply_err(req, EINVAL);
> + return;
> + }
> +
> err = lo_do_open(lo, inode, -1, fi);
> lo_inode_put(lo, &inode);
> if (err) {
> --
> 2.31.1
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK