On Tue, Oct 13, 2026 at 12:01:58AM +0200, Filip Hejsek wrote:
> Use qemu_dup() to ensure the cloexec flag is set on dup'd fds.
>
> The following dup() instances were left unchanged:
>
> FILE REASON
> util/osdep.c implementation of qemu_dup
> migration/cpr-exec.c fd is intentionally kept across exec
IMHO that should use qemu_dup() too, and then explicitly
clear the O_CLOEXEC flag so intended behaviour is clear.
Right now it looks like a mistaken failure to use qemu_dup.
> {linux,bsd}-user/* guest syscalls
That's fine
> tests/* left for future work
Why not fix them now ? There are only a few uses which look suitable
to change.
>
> Signed-off-by: Filip Hejsek <[email protected]>
> ---
> For each call I replaced, I checked how the resulting fd is used
> afterwards. In summary:
>
> hw/virtio/virtio.c:
> the fd is passed to memory_region_init_ram_from_fd, used for mmaping
>
> io/channel-file.c:
> the fd is passed to qio_channel_file_new_fd, used for reading/writing
>
> qemu-nbd.c:
> the fd is stored into old_stderr, then dup2'd back to STDERR_FILENO
>
> system/vl.c:
> no change in behavior, the code was already setting the cloexec flag
>
> ui/dmabuf.c:
> the function is called by qemu_spice_gl_update, which passes the fds
> to SPICE server
>
> These uses shouldn't require keeping the fd open across exec.
>
> Changes in v2:
> - Replace the use in qemu-nbd.c too
> - Changed commit message
> - Link to v1:
> https://lore.kernel.org/qemu-devel/[email protected]
> ---
> hw/virtio/virtio.c | 2 +-
> io/channel-file.c | 2 +-
> qemu-nbd.c | 2 +-
> system/vl.c | 9 +--------
> ui/dmabuf.c | 2 +-
> 5 files changed, 5 insertions(+), 12 deletions(-)
>
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index c9f9e5b511..70779fbd56 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -3204,7 +3204,7 @@ VirtioSharedMemoryMapping
> *virtio_shared_memory_mapping_new(uint8_t shmid,
> return NULL;
> }
>
> - fd = dup(fd);
> + fd = qemu_dup(fd);
> if (fd < 0) {
> error_report("Failed to duplicate fd: %s", strerror(errno));
> return NULL;
> diff --git a/io/channel-file.c b/io/channel-file.c
> index 5cef75a67c..3f707e80c9 100644
> --- a/io/channel-file.c
> +++ b/io/channel-file.c
> @@ -48,7 +48,7 @@ qio_channel_file_new_fd(int fd)
> QIOChannelFile *
> qio_channel_file_new_dupfd(int fd, Error **errp)
> {
> - int newfd = dup(fd);
> + int newfd = qemu_dup(fd);
>
> if (newfd < 0) {
> error_setg_errno(errp, errno, "Could not dup FD %d", fd);
> diff --git a/qemu-nbd.c b/qemu-nbd.c
> index ed5895861b..db1a70b008 100644
> --- a/qemu-nbd.c
> +++ b/qemu-nbd.c
> @@ -975,7 +975,7 @@ int main(int argc, char **argv)
>
> /* Remember parent's stderr if we will be restoring it. */
> if (opts.verbose /* fork_process is set */) {
> - opts.old_stderr = dup(STDERR_FILENO);
> + opts.old_stderr = qemu_dup(STDERR_FILENO);
> if (opts.old_stderr < 0) {
> error_report("Could not dup original stderr: %s",
> strerror(errno));
> diff --git a/system/vl.c b/system/vl.c
> index 468a9fc247..9381e3d7f7 100644
> --- a/system/vl.c
> +++ b/system/vl.c
> @@ -614,14 +614,7 @@ static int parse_add_fd(void *opaque, QemuOpts *opts,
> Error **errp)
> return -1;
> }
>
> -#ifdef F_DUPFD_CLOEXEC
> - dupfd = fcntl(fd, F_DUPFD_CLOEXEC, 0);
> -#else
> - dupfd = dup(fd);
> - if (dupfd != -1) {
> - qemu_set_cloexec(dupfd);
> - }
> -#endif
> + dupfd = qemu_dup(fd);
> if (dupfd == -1) {
> error_setg_errno(errp, errno, "error duplicating fd");
> return -1;
> diff --git a/ui/dmabuf.c b/ui/dmabuf.c
> index 497f82cc61..6d5dffdf84 100644
> --- a/ui/dmabuf.c
> +++ b/ui/dmabuf.c
> @@ -95,7 +95,7 @@ void qemu_dmabuf_dup_fds(QemuDmaBuf *dmabuf, int *fds, int
> nfds)
> assert(nfds >= dmabuf->num_planes);
>
> for (i = 0; i < dmabuf->num_planes; i++) {
> - fds[i] = dmabuf->fd[i] >= 0 ? dup(dmabuf->fd[i]) : -1;
> + fds[i] = dmabuf->fd[i] >= 0 ? qemu_dup(dmabuf->fd[i]) : -1;
> }
> }
>
>
> ---
> base-commit: 615ece3c406b262996e569f29ea6eed0d81c4d8d
> change-id: 20261012-use-qemu-dup-38628dbac3ee
>
> Best regards,
> --
> Filip Hejsek <[email protected]>
>
With regards,
Daniel
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