[no subject]

[Collin Funk]

Hi all,

Christian Brauner <brauner@xxxxxxxxxx> wrote:

> On Sun, 31 May 2026 01:01:04 +0000, Askar Safin wrote:
> > This patchset is for VFS.
> > 
> > Recently we got a lot of vulnerabilities in splice/vmsplice.
> > 
> > Also vmsplice already was source of vulnerabilities in the past:
> > CVE-2020-29374 (see https://lwn.net/Articles/849638/ ).
> > 
> > [...]
> 
> Applied to the vfs-7.2.vmsplice branch of the vfs/vfs.git tree.
> Patches in the vfs-7.2.vmsplice branch should appear in linux-next soon.
> 
> Please report any outstanding bugs that were missed during review in a
> new review to the original patch series allowing us to drop it.
> 
> It's encouraged to provide Acked-bys and Reviewed-bys even though the
> patch has now been applied. If possible patch trailers will be updated.
> 
> Note that commit hashes shown below are subject to change due to rebase,
> trailer updates or similar. If in doubt, please check the listed branch.
> 
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
> branch: vfs-7.2.vmsplice
> 
> [1/3] tee: fs/splice.c: remove unused parameter "flags" from "link_pipe"
>       https://git.kernel.org/vfs/vfs/c/a9f7db50ed2f
> [2/3] vmsplice: make vmsplice a trivial wrapper for preadv2/pwritev2
>       https://git.kernel.org/vfs/vfs/c/e2c0b2368081
> [3/3] splice: remove PIPE_BUF_FLAG_GIFT
>       https://git.kernel.org/vfs/vfs/c/7d75aa8edfce

In GNU coreutils-9.11, released 2026-04-20, Pádraig Brady added the use
of splice and vmsplice to the 'yes' command [1]. Afterward, I added the
use of splice to the 'cat' command, which is now used if copy_file_range
fails or cannot be used [2]. There were some minor adjustments that had
to be made to those patches pre-release. However, as far as I am aware,
they have not had any issues yet which was a bit surprising to me at
least. Now it seems we are a bit unlucky with our timing...

Anyways, I figured you may be interested in seeing how these changes
affect some applications. I built a kernel from the vfs-7.2.vmsplice
branch and used a config based on my recent Fedora kernel.

Here is the throughput on my Fedora kernel:

    $ uname -r
    7.0.10-201.fc44.x86_64
    $ yes --version | head -n 1
    yes (GNU coreutils) 9.11.50-157bd
    $ timeout 1m taskset 1 yes | taskset 2 pv -r > /dev/null
    [36.9GiB/s]
    $ cat --version | head -n 1
    cat (GNU coreutils) 9.11.50-157bd
    $ timeout 1m taskset 1 cat /dev/zero | taskset 2 pv -r > /dev/null
    [9.34GiB/s]

Here is the throughput on the vfs-7.2.vmsplice kernel:

    $ uname -r
    7.1.0-rc1+
    $ yes --version | head -n 1
    yes (GNU coreutils) 9.11.50-157bd
    $ timeout 1m taskset 1 yes | taskset 2 pv -r > /dev/null
    [3.41GiB/s]
    $ cat --version | head -n 1
    cat (GNU coreutils) 9.11.50-157bd
    $ timeout 1m taskset 1 cat /dev/zero | taskset 2 pv -r > /dev/null
    [9.50GiB/s]

Unsurprisingly, 'cat' is not affected since it does not use vmsplice. On
the other hand 'yes' is 10x slower. I dislike this, obviously. However,
of course I realize that the average person uses the 'yes' command much
less frequently than I do, if they use it at all. To them security is a
far greater concern. Just want to make it clear that this message isn't
an attempt at getting this change reverted or anything like that.

Anyways, hope the testing was at least somewhat useful.

Collin

[1] https://github.com/coreutils/coreutils/commit/2b1c059e6a06eebbb721d010b1221ec54200cc33
[2] https://github.com/coreutils/coreutils/commit/457f88513a128ce91160c4a60f821cc1612204be

P.S. It would be fun to test this branch on the machine where we got
'yes' to output at 175GiB/s. Sadly we do not have root access on it to
install a new kernel, though.