Re: [Virtio-fs] [PULL 00/12] virtiofs queue

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

* Vivek Goyal (vgoyal@redhat.com) wrote:
> On Wed, Feb 16, 2022 at 07:40:14PM +0000, Dr. David Alan Gilbert wrote:
> > * Dr. David Alan Gilbert (git) (dgilbert@redhat.com) wrote:
> > > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > > 
> > > The following changes since commit c13b8e9973635f34f3ce4356af27a311c993729c:
> > > 
> > >   Merge remote-tracking branch 'remotes/alistair/tags/pull-riscv-to-apply-20220216' into staging (2022-02-16 09:57:11 +0000)
> > > 
> > > are available in the Git repository at:
> > > 
> > >   https://gitlab.com/dagrh/qemu.git tags/pull-virtiofs-20220216
> > > 
> > > for you to fetch changes up to 47cc3ef597b2ee926c13c9433f4f73645429e128:
> > > 
> > >   virtiofsd: Add basic support for FUSE_SYNCFS request (2022-02-16 17:29:32 +0000)
> > 
> > NAK
> > this doesn't build on older Linuxes.
> > 
> > Rework version in the works.
> 
> Hi David,
> 
> I think it is patch 8 which is using gettid(). I have updated that
> patch and now I am using syscall(NR_gettid) instead. Here is the
> updated patch. I hope this solves the build on older Linux issue.
> 
> 
> Subject: virtiofsd: Add helpers to work with /proc/self/task/tid/attr/fscreate
> 
> Soon we will be able to create and also set security context on the file
> atomically using /proc/self/task/tid/attr/fscreate knob. If this knob
> is available on the system, first set the knob with the desired context
> and then create the file. It will be created with the context set in
> fscreate. This works basically for SELinux and its per thread.
> 
> This patch just introduces the helper functions. Subsequent patches will
> make use of these helpers.
> 
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

Thanks, I'll merge that in.

Dave

> ---
>  tools/virtiofsd/passthrough_ll.c |   92 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 92 insertions(+)
> 
> Index: rhvgoyal-qemu/tools/virtiofsd/passthrough_ll.c
> ===================================================================
> --- rhvgoyal-qemu.orig/tools/virtiofsd/passthrough_ll.c	2022-02-16 15:53:13.657015138 -0500
> +++ rhvgoyal-qemu/tools/virtiofsd/passthrough_ll.c	2022-02-16 15:55:14.911234993 -0500
> @@ -173,10 +173,14 @@ struct lo_data {
>  
>      /* An O_PATH file descriptor to /proc/self/fd/ */
>      int proc_self_fd;
> +    /* An O_PATH file descriptor to /proc/self/task/ */
> +    int proc_self_task;
>      int user_killpriv_v2, killpriv_v2;
>      /* If set, virtiofsd is responsible for setting umask during creation */
>      bool change_umask;
>      int user_posix_acl, posix_acl;
> +    /* Keeps track if /proc/<pid>/attr/fscreate should be used or not */
> +    bool use_fscreate;
>  };
>  
>  static const struct fuse_opt lo_opts[] = {
> @@ -257,6 +261,72 @@ static struct lo_data *lo_data(fuse_req_
>  }
>  
>  /*
> + * Tries to figure out if /proc/<pid>/attr/fscreate is usable or not. With
> + * selinux=0, read from fscreate returns -EINVAL.
> + *
> + * TODO: Link with libselinux and use is_selinux_enabled() instead down
> + * the line. It probably will be more reliable indicator.
> + */
> +static bool is_fscreate_usable(struct lo_data *lo)
> +{
> +    char procname[64];
> +    int fscreate_fd;
> +    size_t bytes_read;
> +
> +    sprintf(procname, "%ld/attr/fscreate", syscall(SYS_gettid));
> +    fscreate_fd = openat(lo->proc_self_task, procname, O_RDWR);
> +    if (fscreate_fd == -1) {
> +        return false;
> +    }
> +
> +    bytes_read = read(fscreate_fd, procname, 64);
> +    close(fscreate_fd);
> +    if (bytes_read == -1) {
> +        return false;
> +    }
> +    return true;
> +}
> +
> +/* Helpers to set/reset fscreate */
> +__attribute__((unused))
> +static int open_set_proc_fscreate(struct lo_data *lo, const void *ctx,
> +                                  size_t ctxlen,int *fd)
> +{
> +    char procname[64];
> +    int fscreate_fd, err = 0;
> +    size_t written;
> +
> +    sprintf(procname, "%ld/attr/fscreate", syscall(SYS_gettid));
> +    fscreate_fd = openat(lo->proc_self_task, procname, O_WRONLY);
> +    err = fscreate_fd == -1 ? errno : 0;
> +    if (err) {
> +        return err;
> +    }
> +
> +    written = write(fscreate_fd, ctx, ctxlen);
> +    err = written == -1 ? errno : 0;
> +    if (err) {
> +        goto out;
> +    }
> +
> +    *fd = fscreate_fd;
> +    return 0;
> +out:
> +    close(fscreate_fd);
> +    return err;
> +}
> +
> +__attribute__((unused))
> +static void close_reset_proc_fscreate(int fd)
> +{
> +    if ((write(fd, NULL, 0)) == -1) {
> +        fuse_log(FUSE_LOG_WARNING, "Failed to reset fscreate. err=%d\n", errno);
> +    }
> +    close(fd);
> +    return;
> +}
> +
> +/*
>   * Load capng's state from our saved state if the current thread
>   * hadn't previously been loaded.
>   * returns 0 on success
> @@ -3522,6 +3592,15 @@ static void setup_namespaces(struct lo_d
>          exit(1);
>      }
>  
> +    /* Get the /proc/self/task descriptor */
> +    lo->proc_self_task = open("/proc/self/task/", O_PATH);
> +    if (lo->proc_self_task == -1) {
> +        fuse_log(FUSE_LOG_ERR, "open(/proc/self/task, O_PATH): %m\n");
> +        exit(1);
> +    }
> +
> +    lo->use_fscreate = is_fscreate_usable(lo);
> +
>      /*
>       * We only need /proc/self/fd. Prevent ".." from accessing parent
>       * directories of /proc/self/fd by bind-mounting it over /proc. Since / was
> @@ -3738,6 +3817,14 @@ static void setup_chroot(struct lo_data
>          exit(1);
>      }
>  
> +    lo->proc_self_task = open("/proc/self/task", O_PATH);
> +    if (lo->proc_self_fd == -1) {
> +        fuse_log(FUSE_LOG_ERR, "open(\"/proc/self/task\", O_PATH): %m\n");
> +        exit(1);
> +    }
> +
> +    lo->use_fscreate = is_fscreate_usable(lo);
> +
>      /*
>       * Make the shared directory the file system root so that FUSE_OPEN
>       * (lo_open()) cannot escape the shared directory by opening a symlink.
> @@ -3923,6 +4010,10 @@ static void fuse_lo_data_cleanup(struct
>          close(lo->proc_self_fd);
>      }
>  
> +    if (lo->proc_self_task >= 0) {
> +        close(lo->proc_self_task);
> +    }
> +
>      if (lo->root.fd >= 0) {
>          close(lo->root.fd);
>      }
> @@ -3950,6 +4041,7 @@ int main(int argc, char *argv[])
>          .posix_lock = 0,
>          .allow_direct_io = 0,
>          .proc_self_fd = -1,
> +        .proc_self_task = -1,
>          .user_killpriv_v2 = -1,
>          .user_posix_acl = -1,
>      };
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK