From 7b223e38603de3a75602e14914d26f9d4baf52eb Mon Sep 17 00:00:00 2001

From: Christian Ehrhardt <christian.ehrhardt@canonical.com>

Date: Wed, 9 Feb 2022 12:14:56 +0100

Subject: [PATCH 1/2] tools/virtiofsd: Add rseq syscall to the seccomp

 allowlist

The virtiofsd currently crashes when used with glibc 2.35.

That is due to the rseq system call being added to every thread

creation [1][2].

[1]: https://www.efficios.com/blog/2019/02/08/linux-restartable-sequences/

[2]: https://sourceware.org/pipermail/libc-alpha/2022-February/136040.html

This happens not at daemon start, but when a guest connects

    /usr/lib/qemu/virtiofsd -f --socket-path=/tmp/testvfsd -o sandbox=chroot \

        -o source=/var/guests/j-virtiofs --socket-group=kvm

    virtio_session_mount: Waiting for vhost-user socket connection...

    # start ok, now guest will connect

    virtio_session_mount: Received vhost-user socket connection

    virtio_loop: Entry

    fv_queue_set_started: qidx=0 started=1

    fv_queue_set_started: qidx=1 started=1

    Bad system call (core dumped)

We have to put rseq on the seccomp allowlist to avoid that the daemon

is crashing in this case.

Reported-by: Michael Hudson-Doyle <michael.hudson@canonical.com>

Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

Message-id: 20220209111456.3328420-1-christian.ehrhardt@canonical.com

[Moved rseq to its alphabetically ordered position in the seccomp

allowlist.

--Stefan]

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

---

 tools/virtiofsd/passthrough_seccomp.c | 3 +++

 1 file changed, 3 insertions(+)

diff --git a/tools/virtiofsd/passthrough_seccomp.c b/tools/virtiofsd/passthrough_seccomp.c

index a3ce9f898d..2bc0127b69 100644

--- a/tools/virtiofsd/passthrough_seccomp.c

+++ b/tools/virtiofsd/passthrough_seccomp.c

@@ -91,6 +91,9 @@ static const int syscall_allowlist[] = {

     SCMP_SYS(renameat2),

     SCMP_SYS(removexattr),

     SCMP_SYS(restart_syscall),

+#ifdef __NR_rseq

+    SCMP_SYS(rseq), /* required since glibc 2.35 */

+#endif

     SCMP_SYS(rt_sigaction),

     SCMP_SYS(rt_sigprocmask),

     SCMP_SYS(rt_sigreturn),

-- 

2.35.1